RESUMEN
BACKGROUND: Myocardial perfusion imaging (MPI) with 82Rb PET/CT is increasingly utilized in the evaluation of coronary artery disease with high diagnostic accuracy. Various softwares for data processing have been developed over the years with conflicting data regarding their reproducibility. In this study, we compared the quantitative results of myocardial perfusion and exam classification from three different softwares. METHODS: Data from consecutive patients who have undergone rest/stress 82Rb PET/CT MPI at the Royal Brompton & Harefield Trust, London, were analyzed. All data were processed using the Corridor 4DM (Invia, Ann Arbor, Michigan, USA), QPET (Cedars-Sinai, Los Angeles, California, USA), and SyngoMBF (Siemens Healthineers, Erlangen, Germany). The software packages addressed Lortie tracer kinetic model and region of interest (ROI) extraction correction option. STATISTICS: A repeated-measures ANOVA with a Greenhouse-Geisser correction was performed with post hoc tests using Bonferroni correction. For intersoftware variability, Pearson correlation and intraclass correlation coefficients (ICC) were calculated. Bland-Altman assessed limit of agreement. Cohen's Kappa assessed agreement in the classification of exams as normal or abnormal using an MFR cut-off value of 2.0. A P value of less than 0.05 was considered statistically significant. RESULTS: Data from 55 patients were analyzed. The mean values of myocardial blood flow (MBF) and myocardial perfusion reserve (MFR) were statistically significantly different among the softwares (P < 0.05). Corridor4DM had considerably lower values of MFR and classified a more substantial number of exams as abnormal (MFR: 2.21 ± 0.7, 2.4 ± 0.8, and 1.98 ± 0.8; and 18, 15, and 31 exams were abnormal for Syngo, QPET, and Corridor4DM, respectively). Accordingly, kappa agreement was moderate for Syngo vs QPET (k > 0.5), but minimal for Corridor4DM in comparison to its pairs (k < 0.4). CONCLUSION: Users should be cautious when using different software interchangeably as systematic differences amongst them may introduce more extensive quantitative variation which could be clinically significant.
Asunto(s)
Enfermedad de la Arteria Coronaria/diagnóstico por imagen , Corazón/diagnóstico por imagen , Procesamiento de Imagen Asistido por Computador/métodos , Imagen de Perfusión Miocárdica , Tomografía de Emisión de Positrones , Programas Informáticos , Anciano , Circulación Coronaria , Femenino , Humanos , Masculino , Persona de Mediana Edad , Tomografía Computarizada por Tomografía de Emisión de Positrones , Reproducibilidad de los Resultados , Estudios Retrospectivos , Radioisótopos de Rubidio , Imagen de Cuerpo EnteroRESUMEN
OBJECTIVES: Despite advances in non-invasive myocardial perfusion imaging (MPI) evaluation, computed tomography (CT) multiphase MPI protocols have not yet been compared with the highly accurate rubidium-82 positron emission tomography (82RbPET) MPI. Thus, this study aimed to evaluate agreement between 82RbPET and 320-detector row CT (320-CT) MPI using a multiphase protocol in suspected CAD patients. METHODS: Forty-four patients referred for MPI evaluation were prospectively enrolled and underwent dipyridamole stress 82RbPET and multiphase 320-CT MPI (five consecutive volumetric acquisitions during stress). Statistical analyses were performed using the R software. RESULTS: There was high agreement for recognizing summed stress scores ≥ 4 (kappa 0.77, 95% CI 0.55-0.98, p < 0.001) and moderate for detecting SDS ≥ 2 (kappa 0.51, 95% CI 0.23-0.80, p < 0.001). In a per segment analysis, agreement was high for the presence of perfusion defects during stress and rest (kappa 0.75 and 0.82, respectively) and was moderate for impairment severity (kappa 0.58 and 0.65, respectively). The 320-CT protocol was safe, with low radiation burden (9.3 ± 2.4 mSv). CONCLUSIONS: There was a significant agreement between dipyridamole stress 320-CT MPI and 82RbPET MPI in the evaluation of suspected CAD patients of intermediate risk. The multiphase 320-CT MPI protocol was feasible, diagnostic and with relatively low radiation exposure. KEY POINTS: ⢠Rubidium-82 PET and 320-MDCT can perform MPI studies for CAD investigation. ⢠There is high agreement between rubidium-82 PET and 320-MDCT for MPI assessment. ⢠Multiphase CT perfusion protocols are feasible and with low radiation. ⢠Multiphase CT perfusion protocols can identify image artefacts.
Asunto(s)
Enfermedad de la Arteria Coronaria/diagnóstico por imagen , Radiofármacos , Radioisótopos de Rubidio , Angiografía por Tomografía Computarizada , Vasos Coronarios/diagnóstico por imagen , Dipiridamol/farmacología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Tomografía Computarizada Multidetector , Imagen de Perfusión Miocárdica/métodos , Tomografía de Emisión de Positrones/métodos , Estudios Prospectivos , Programas Informáticos , Tomografía Computarizada de Emisión de Fotón Único/métodos , Vasodilatadores/farmacologíaRESUMEN
PURPOSE: Myocardial perfusion imaging (MPI) with 99mTc-sestamibi (sestamibi) SPECT and rubidium-82 (82Rb) PET both allow for combined assessment of perfusion and left ventricular (LV) function. We sought to compare parameters of LV function obtained with both methods using a single dipyridamole stress dose. MATERIALS AND METHODS: A group of 221 consecutive patients (65.2 ± 10.4 years, 52.9% male) underwent consecutive sestamibi and 82Rb MPI after a single dipyridamole stress dose. Sestamibi and 82Rb summed rest (SRS), stress (SSS) and difference (SDS) scores, and LV end-diastolic (EDV) and end-systolic (ESV) volumes and left ventricular ejection fraction (LVEF) were compared. RESULTS: Bland-Altman analysis showed that with increasing ESV and EDV the difference between the two perfusion tracers increased both at rest and post-stress. The mean difference in EDV and ESV between the two perfusion tracers at rest could both be independently explained by the 82Rb SDS and the sestamibi SRS. The combined models explained approximately 30% of the variation in these volumes between the two perfusion tracers (R2 = 0.261, p = 0.005; R2 = 0.296, p < 0.001, for EDV and ESV respectively). However, the mean difference in LVEF between sestamibi and 82Rb showed no significant trend post-stress (R2 = 0.001, p = 0.70) and only a modest linear increase with increasing LVEF values at rest (R2 = 0.032, p = 0.009). CONCLUSIONS: Differences in left ventricular volumes between sestamibi and 82Rb MPI increase with increasing volumes. However, these differences did only marginally affect LVEF between sestamibi and 82Rb. In clinical practice these results should be taken into account when comparing functional derived parameters between sestamibi and 82Rb MPI.
Asunto(s)
Tomografía Computarizada por Emisión de Fotón Único Sincronizada Cardíaca , Dipiridamol/farmacología , Imagen de Perfusión Miocárdica , Tomografía de Emisión de Positrones , Radioisótopos de Rubidio , Tecnecio Tc 99m Sestamibi , Función Ventricular Izquierda/efectos de los fármacos , Anciano , Electrocardiografía , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Estrés Fisiológico/efectos de los fármacos , Función Ventricular Izquierda/fisiologíaRESUMEN
OBJECTIVES: Perfusion abnormalities are frequently seen in Single Photon Emission Computed Tomography (SPECT) when a left bundle branch block is present. A few studies have shown decreased coronary flow reserve in the left anterior descending territory, regardless of the presence of coronary artery disease. OBJECTIVE: We sought to investigate rubidium-82 (82Rb) positron emission tomography imaging in the assessment of myocardial blood flow and coronary flow reserve in patients with left bundle branch block. METHODS: Thirty-eight patients with left bundle branch block (GI), median age 63.5 years, 22 (58%) female, 12 with coronary artery disease (≥70%; GI-A) and 26 with no evidence of significant coronary artery disease (GI-B), underwent rest-dipyridamole stress 82Rb-positron emission tomography with absolute quantitative flow measurements using Cedars-Sinai software (mL/min/g). The relative myocardial perfusion and left ventricular ejection fraction were assessed in 17 segments. These parameters were compared with those obtained from 30 patients with normal 82Rb-positron emission tomography studies and without left bundle branch block (GII). RESULTS: Stress myocardial blood flow and coronary flow reserve were significantly lower in GI than in GII (p<0.05). The comparison of coronary flow reserve between GI-A and GI-B showed that it was different from the global coronary flow reserve (p<0.05) and the stress flow was significantly lower in the anterior than in the septal wall for both groups. Perfusion abnormalities were more prevalent in GI-A (p=0.06) and the left ventricular ejection fraction was not different between GI-A and GI-B, whereas it was lower in GI than in GII (p<0.001). CONCLUSION: The data confirm that patients with left bundle branch block had decreased myocardial blood flow and coronary flow reserve and coronary flow reserve assessed by 82Rb-positron emission tomography imaging may be useful in identifying coronary artery disease in patients with left bundle branch block.
Asunto(s)
Bloqueo de Rama/diagnóstico por imagen , Enfermedad de la Arteria Coronaria/diagnóstico por imagen , Circulación Coronaria/fisiología , Tomografía de Emisión de Positrones/métodos , Anciano , Bloqueo de Rama/fisiopatología , Enfermedad de la Arteria Coronaria/fisiopatología , Femenino , Reserva del Flujo Fraccional Miocárdico/fisiología , Humanos , Masculino , Persona de Mediana Edad , Imagen de Perfusión Miocárdica/métodos , Radioisótopos de Rubidio , Volumen Sistólico/fisiologíaRESUMEN
OBJECTIVES: Perfusion abnormalities are frequently seen in Single Photon Emission Computed Tomography (SPECT) when a left bundle branch block is present. A few studies have shown decreased coronary flow reserve in the left anterior descending territory, regardless of the presence of coronary artery disease. OBJECTIVE: We sought to investigate rubidium-82 (82Rb) positron emission tomography imaging in the assessment of myocardial blood flow and coronary flow reserve in patients with left bundle branch block. METHODS: Thirty-eight patients with left bundle branch block (GI), median age 63.5 years, 22 (58%) female, 12 with coronary artery disease (≥70%; GI-A) and 26 with no evidence of significant coronary artery disease (GI-B), underwent rest-dipyridamole stress 82Rb-positron emission tomography with absolute quantitative flow measurements using Cedars-Sinai software (mL/min/g). The relative myocardial perfusion and left ventricular ejection fraction were assessed in 17 segments. These parameters were compared with those obtained from 30 patients with normal 82Rb-positron emission tomography studies and without left bundle branch block (GII). RESULTS: Stress myocardial blood flow and coronary flow reserve were significantly lower in GI than in GII (p<0.05). The comparison of coronary flow reserve between GI-A and GI-B showed that it was different from the global coronary flow reserve (p<0.05) and the stress flow was significantly lower in the anterior than in the septal wall for both groups. Perfusion abnormalities were more prevalent in GI-A (p=0.06) and the left ventricular ejection fraction was not different between GI-A and GI-B, whereas it was lower in GI than in GII (p<0.001). CONCLUSION: The data confirm that patients with left bundle branch block had decreased myocardial blood flow and coronary flow reserve and coronary flow reserve assessed by 82Rb-positron emission tomography imaging may be useful in identifying coronary artery disease in patients with left bundle branch block.
Asunto(s)
Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , Bloqueo de Rama , Enfermedad de la Arteria Coronaria , Circulación Coronaria/fisiología , Tomografía de Emisión de Positrones/métodos , Bloqueo de Rama/fisiopatología , Enfermedad de la Arteria Coronaria/fisiopatología , Reserva del Flujo Fraccional Miocárdico/fisiología , Imagen de Perfusión Miocárdica/métodos , Radioisótopos de Rubidio , Volumen Sistólico/fisiologíaRESUMEN
An increase in extracellular KCl ([KCl]o) occurs under various pathological conditions in the retina, leading to retinal swelling and possible neuronal damage. The mechanisms of this KCl o-induced retinal swelling were investigated in the present study, with emphasis on the Cl- transport mechanisms. Increasing [KCl]o (from 5 to 70 mM) led to concentration-dependent swelling in chicken retinas. The curve relating the degree of swelling to [KCl]o was biphasic, with one component from 5 to 35 mM [KCl]o and another from 35 to 100 mM. As Cl- omission prevented swelling in all conditions, the effect of cotransporter or Cl- channel blockers was examined to investigate the mechanisms of Cl- influx. The cotransporter blockers bumetanide and DIOA reduced swelling by 68% and 76%, respectively at [KCl]o 25 mM (K25), and by 14-17% at [KCl]o 54 mM (K54). The Cl- channel blockers NPPB and niflumic acid did not affect swelling at K25 but reduced it by 90-95% at K54 (NPPB IC50 60.7 microM). Furosemide showed an atypical effect, decreasing swelling by 14% at K25 and by 95% at K54 (IC50 173.9 microM). Na+ omission decreased swelling at K25 but not at K54. These results suggest the contribution of cotransporters to Cl- influx at K25 and of Cl- channels at K54. At K25, swelling was found in the ganglion cell layer and in the lower half of the inner nuclear layer. With K54, swelling occurred in all inner retinal layers. The ganglion cell layer swelling was due to both Muller cell end-foot and ganglion cell soma swelling. K54 also induced ganglion cell damage as shown by disorganized, pyknotic and refringent nuclei.
Asunto(s)
Cloruros/metabolismo , Papiledema/metabolismo , Cloruro de Potasio/farmacología , Células Ganglionares de la Retina/metabolismo , Acetatos/farmacología , Animales , Bumetanida/farmacología , Pollos , Canales de Cloruro/antagonistas & inhibidores , Canales de Cloruro/metabolismo , Diuréticos/farmacología , Antagonistas de Aminoácidos Excitadores/farmacología , Indenos/farmacología , Nitrobenzoatos/farmacología , Papiledema/inducido químicamente , Papiledema/patología , Potasio/metabolismo , Receptores de Glutamato/metabolismo , Células Ganglionares de la Retina/efectos de los fármacos , Células Ganglionares de la Retina/patología , Radioisótopos de Rubidio , Inhibidores del Simportador de Cloruro Sódico y Cloruro Potásico , Simportadores de Cloruro de Sodio-Potasio/metabolismoRESUMEN
We report a study on the effect of the fluorescent probe eosin on some of the reactions involved in the conformational transitions that lead to the occlusion of the K(+)-congener Rb(+) in the Na(+)/K(+)-ATPase. Eosin decreases the equilibrium levels of occluded Rb(+), this effect being fully attributable to a decrease in the apparent affinity of the enzyme for Rb(+) since the capacity for occlusion remains independent of eosin concentration. The results can be quantitatively described by a model that assumes that two molecules of eosin are able to bind to the Na(+)/K(+)-ATPase, both to the Rb(+)-free and to the Rb(+)-occluded enzyme regardless of the degree of cation occlusion. Concerning the effect on the affinity for Rb(+) occlusion, transient state experiments show that eosin reduces the initial velocity of occlusion, and that, like ATP, it increases the velocity of deocclusion of Rb(+). Interactions between eosin and ATP on Rb(+)-release experiments seem to indicate that eosin binds to the low-affinity site of ATP from which it exerts effects that are similar to those of the nucleotide.
Asunto(s)
Eosina Amarillenta-(YS)/química , Eosina Amarillenta-(YS)/farmacocinética , Colorantes Fluorescentes/química , Colorantes Fluorescentes/farmacocinética , Radioisótopos de Rubidio/farmacocinética , ATPasa Intercambiadora de Sodio-Potasio/química , ATPasa Intercambiadora de Sodio-Potasio/farmacocinética , Adenosina Trifosfato/química , Adenosina Trifosfato/farmacocinética , Animales , Sitios de Unión , Modelos Químicos , Dinámicas no Lineales , Unión Proteica , Conformación Proteica , Porcinos , Termodinámica , Factores de TiempoRESUMEN
The relationship between cell volume and K(+) transmembrane fluxes of goldfish (Carassius auratus) hepatocytes exposed to anisotonic conditions or energetic limitation was studied and compared with the response of hepatocytes from trout (Oncorhynchus mykiss) and rat (Rattus rattus). Cell volume was studied by video- and fluorescence microscopy, while K(+) fluxes were assessed by measuring unidirectional (86)Rb(+) fluxes. In trout and rat hepatocytes, hyposmotic (180 mosmoll(-1)) exposure at pH 7.45 caused cell swelling followed by a regulatory volume decrease (RVD), a response reported to be mediated by net efflux of KCl and osmotically obliged water. By contrast, goldfish hepatocytes swelled but showed no RVD under these conditions. Although in goldfish hepatocytes a net ((86)Rb(+))K(+) efflux could be activated by N-ethylmaleimide, this flux was not, or only partially, activated by hyposmotic swelling (120-180 mosmoll(-1)). Blockage of glycolysis by iodoacetic acid (IAA) did not alter cell volume in goldfish hepatocytes, whereas in the presence of cyanide (CN(-)), an inhibitor of oxidative phosphorylation, or CN(-) plus IAA (CN(-)+IAA), cell volume decreased by 3-7%. Although in goldfish hepatocytes, energetic limitation had no effect on ((86)Rb(+))K(+) efflux, ((86)Rb(+))K(+) influx decreased by 57-66% in the presence of CN(-) and CN(-)+IAA but was not significantly altered by IAA alone. Intracellular K(+) loss after 20 min of exposure to CN(-) and CN(-)+IAA amounted to only 3% of the total intracellular K(+). Collectively, these observations suggest that goldfish hepatocytes, unlike hepatocytes of anoxia-intolerant species, avoid a decoupling of transmembrane K(+) fluxes in response to an osmotic challenge. This may underlie both the inability of swollen cells to undergo RVD but also the capability of anoxic cells to maintain intracellular K(+) concentrations that are almost unaltered, thereby prolonging cell survival.
Asunto(s)
Carpa Dorada/fisiología , Hepatocitos/metabolismo , Potasio/metabolismo , Trucha/fisiología , Anaerobiosis , Animales , Transporte Biológico/fisiología , Tamaño de la Célula/efectos de los fármacos , Tamaño de la Célula/fisiología , Cianuros/farmacología , Hepatocitos/citología , Hepatocitos/efectos de los fármacos , Concentración de Iones de Hidrógeno , Soluciones Hipertónicas/farmacología , Soluciones Hipotónicas/farmacología , Ácido Yodoacético/farmacología , Masculino , Microscopía Fluorescente , Cloruro de Potasio/farmacología , Ratas , Ratas Wistar , Radioisótopos de Rubidio , Sodio/metabolismo , Agua/fisiologíaRESUMEN
The K+ uptake pathways in yeast mitochondria are still undefined. Nonetheless, the K+-mediated mitochondrial swelling observed in the absence of phosphate (PO4) and in the presence of a respiratory substrate has led to propose that large K+ movements occur in yeast mitochondria. Thus, the uptake of K+ by isolated yeast mitochondria was evaluated. Two parallel experiments were conducted to evaluate K+ transport; these were mitochondrial swelling and the uptake of the radioactive K+ analog 86Rb+. The opening of the yeast mitochondrial unspecific channel (YMUC) was regulated by different PO4 concentrations. The high protein concentrations used to measure 86Rb+ uptake resulted in a slight stabilization of the transmembrane potential at 0.4 mM PO4 but not at 0 or 4 mM PO4. At 4 mM PO4 swelling was inhibited while, in contrast, 86Rb+ uptake was still observed. The results suggest that an energy-dependent K+ uptake mechanism was unmasked when the YMUC was closed. To further analyze the properties of this K+ uptake system, the Mg2+ and quinine sensitivity of both swelling and 86Rb+ uptake were evaluated. Under the conditions where the unspecific pore was closed, K+ transport sensitivity to Mg2+ and quinine increased. In addition, when Zn2+ was added as an antiport inhibitor, uptake of 86Rb+ increased. It is suggested that in yeast mitochondria, the K+ concentration is highly regulated by the equilibrium of uptake and exit of this cation through two specific transporters.
Asunto(s)
Membranas Intracelulares/metabolismo , Mitocondrias/metabolismo , Canales de Potasio/fisiología , Potasio/metabolismo , Saccharomyces cerevisiae/metabolismo , Transporte Iónico , Magnesio/farmacología , Potenciales de la Membrana , Mitocondrias/ultraestructura , Dilatación Mitocondrial , Permeabilidad , Fosfatos/farmacología , Quinina/farmacología , Radioisótopos de Rubidio/farmacocinética , Saccharomyces cerevisiae/ultraestructura , Proteínas de Saccharomyces cerevisiaeRESUMEN
We examined the rat proximal tubule (PT) response to endothelin-1 (ET-1) in terms of 20-hydroxyeicosatetraenoic acid (HETE) dependency. Arachidonic acid (AA) (1 microM) decreased ouabain-sensitive (86)Rb uptake from 2.1 +/- 0.1 to 0.3 +/- 0.08 ng Rb. 10 microg protein(-1). 2 min(-1) (P < 0.05); 20-HETE (1 microM) had similar effects. Dibromododecenoic acid (DBDD) (2 microM), an inhibitor of omega-hydroxylase, abolished the inhibitory action of AA on (86)Rb uptake whereas the PT response to 20-HETE was unaffected. ET-1 at 0.1, 1, 10, and 100 nM reduced (86)Rb uptake from 2.8 +/- 0.3 in control PTs to 2.4 +/- 0.2, 1.7 +/- 0.1, 0.67 +/- 0.08, and 0.1 +/- 0.03 ng Rb. 10 microg protein(-1). 2 min(-1), respectively. DBDD (2 microM) abolished the inhibitory effect of ET-1 on (86)Rb uptake as did BMS182874 (1 microM), an ET(A)-selective receptor antagonist. ET-1 (100 nM) significantly increased PT 20-HETE release by approximately 50%, an effect prevented by DBDD. N(omega)-nitro-L-arginine-methyl ester (L-NAME), given for 4 days to inhibit nitric oxide synthase (NOS), increased arterial pressure from 92 +/- 12 to 140 +/- 8 mmHg and increased endogenous release of 20-HETE from isolated PTs (measured by gas chromatography/mass spectrometry). In L-NAME-treated PTs, but not in control PTs, 0.1 microM AA inhibited ouabain-sensitive (86)Rb uptake by > 40%; the response to AA was attenuated by DBDD. We conclude that, in the PTs, 1) 20-HETE is a second messenger for ET-1 and 2) conversion of AA to 20-HETE is augmented when NOS is inhibited.
Asunto(s)
Ácido Araquidónico/farmacocinética , Sistema Enzimático del Citocromo P-450/metabolismo , Endotelina-1/metabolismo , Túbulos Renales Proximales/metabolismo , Animales , Transporte Biológico/fisiología , Antagonistas de los Receptores de Endotelina , Inhibidores Enzimáticos/farmacología , Ácidos Hidroxieicosatetraenoicos/farmacología , Masculino , NG-Nitroarginina Metil Éster/farmacología , Óxido Nítrico/metabolismo , Ratas , Ratas Sprague-Dawley , Receptor de Endotelina A , Receptores de Endotelina/metabolismo , Radioisótopos de Rubidio/farmacocinética , Transducción de Señal/efectos de los fármacos , Transducción de Señal/fisiologíaRESUMEN
Cultured cerebellar granule neurons exposed to gradual reductions in osmolarity (-1.8 mOsm/min) maintained constant volume up to -50% external osmolarity (pi(o)), showing the occurrence of isovolumetric regulation (IVR). Amino acids, Cl-, and K+ contributed at different phases of IVR, with early efflux threshold for [3H]taurine, D-[3H]aspartate (as marker for glutamate) of pi(o) -2% and -19%, respectively, and more delayed thresholds of -30% for [3H]glycine and -25% and -29%, respectively, for Cl- (125I) and K+ (86Rb). Taurine seems preferentially involved in IVR, showing the lowest threshold, the highest efflux rate (five-fold over other amino acids) and the largest cell content decrease. Taurine and Cl- efflux were abolished by niflumic acid and 86Rb by 15 mM Ba2+. Niflumic acid essentially prevented IVR in all ranges of pi(o). Cl--free medium impaired IVR when pi(o) decreased to -24% and Ba2+ blocked it only at a late phase of -30% pi(o). These results indicate that in cerebellar granule neurons: (i) IVR is an active process of volume regulation accomplished by efflux of intracellular osmolytes; (ii) the volume regulation operating at small changes of pi(o) is fully accounted for by mechanisms sensitive to niflumic acid, with contributions of both Cl- and amino acids, particularly taurine; (iii) Cl- contribution to IVR is delayed with respect to other niflumic acid-sensitive osmolyte fluxes (osmolarity threshold of -25% pi(o)); and (iv), K+ fluxes do not contribute to IVR until a late phase (< -30% pi(o)).
Asunto(s)
Tamaño de la Célula , Cerebelo/citología , Neuronas/fisiología , Equilibrio Hidroelectrolítico , Aminoácidos/metabolismo , Animales , Bario/farmacología , Células Cultivadas , Cloruros/administración & dosificación , Cloruros/metabolismo , Medios de Cultivo , Radioisótopos de Yodo/metabolismo , Ácido Niflúmico/farmacología , Concentración Osmolar , Potasio/metabolismo , Ratas , Radioisótopos de Rubidio/metabolismo , Taurina/metabolismoRESUMEN
Radioiodine is used to treat thyroid cancer and hyperthyroidism. In order to reduce radiation hazard to the patient and to people in contact with the patient it would be desirable to obtain the same therapeutic effect with lower activities of the radioisotope. This could be achieved by the simultaneous administration of a compound that increases tissue radiosensitivity. In this study we analyzed the use of nicotinamide (NA) as a radiosensitizer to radioiodine, to increase 131I efficacy. NA administered during 30 days to Wistar rats failed to alter thyroid weight. The influence of NA on radiothyroidectomy induced by increasing doses of 131I was examined in otherwise nontreated rats. NA produced a significant increase in the ablation caused by radioiodine. Goiter was then induced by the administration of methylmercaptoimidazol (MMI) to rats, followed by the treatment with radioiodine with and without simultaneous administration of NA. Thyroid weight per 100 g of body weight ratio was not changed by NA alone; 131I administration caused a 25% decrease in goiter size, while 131I plus NA produced a reduction of the ratio of 46% (p < 0.01 vs. NA). No changes were observed in adenosine diphosphate (ADP)-ribosilation of thyroid nuclear protein in NA-treated rats. Thyroid blood flow (determined by 86Rb uptake) was increased by 84% by NA. In conclusion, nicotinamide has a significant radiosensitizing effect to 131I both in normal and goitrous rats. This action is because of an increase in thyroid blood flow, which probably enhances tissue oxgenation.
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Bocio/radioterapia , Niacinamida/farmacología , Tolerancia a Radiación/efectos de los fármacos , Adenosina Difosfato Ribosa/metabolismo , Animales , Antitiroideos/farmacología , Núcleo Celular/efectos de los fármacos , Femenino , Radioisótopos de Yodo/farmacocinética , Metimazol/farmacología , Ratas , Ratas Wistar , Flujo Sanguíneo Regional/efectos de los fármacos , Radioisótopos de Rubidio/farmacocinética , Glándula Tiroides/irrigación sanguínea , Glándula Tiroides/efectos de los fármacosRESUMEN
A gene, SIT4, was identified as corresponding to a serine/threonine protein phosphatase and when overexpressed confers lithium tolerance in galactose medium to the budding yeast Saccharomyces cerevisiae. This gene has been previously identified as a regulator of the cell cycle and involved in nitrogen sensing. It is shown that the transcription levels of SIT4 are induced by low concentrations of Li(+) in a time-dependent manner. Na(+) and K(+) at high concentrations, but not sorbitol, also induce transcription. As a response to Na(+) or Li(+) stress, yeast cells lower the intracellular K(+) content. This effect is enhanced in cells overexpressing SIT4, which also increase (86)Rb efflux after the addition of Na(+) or Li(+) to the extracellular medium. Another feature of SIT4-overexpressing cells is that they maintain a more alkaline pH of 6.64 compared with 6.17 in the wild type cells. It has been proposed that the main pathway of salt tolerance in yeast is mediated by a P-type ATPase, encoded by PMR2A/ENA1. However, our results show that in a sit4 strain, expression of ENA1 is still induced by monovalent cations, and overexpression of SIT4 does not alter the amount of ENA1 transcript. These results show that SIT4 acts in a parallel pathway not involving induction of transcription of ENA1 and suggest a novel function for SIT4 in response to salt stress.
Asunto(s)
Proteínas de Transporte de Catión , Fosfoproteínas Fosfatasas/metabolismo , Fosfoproteínas Fosfatasas/fisiología , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/enzimología , Adenosina Trifosfatasas/metabolismo , Cationes , Ciclo Celular/fisiología , Citoplasma/metabolismo , Relación Dosis-Respuesta a Droga , Resistencia a Medicamentos , Galactosa/metabolismo , Concentración de Iones de Hidrógeno , Iones , Litio/farmacología , Cloruro de Litio/farmacología , Potasio/farmacología , Proteína Fosfatasa 2 , ARN Mensajero/metabolismo , Proteínas Recombinantes/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Radioisótopos de Rubidio/metabolismo , Sodio/farmacología , Cloruro de Sodio/farmacología , ATPasa Intercambiadora de Sodio-Potasio , Sorbitol/farmacología , Factores de Tiempo , Transcripción GenéticaRESUMEN
The calcium (Ca2+) dependence of potassium (K+) efflux activated by hyposmolarity in cultured cerebellar astrocytes was investigated, measuring in parallel experiments (86)Rb release and changes in cytosolic Ca2+ ([Ca2+]i). Hyposmotic (50%) medium increased [Ca2+]i from 117 to 386 nM, with contributions of extracellular Ca2+ and Ca2+ from the endoplasmic reticulum. Hyposmotic medium increased (86)Rb efflux rate from 0.015 min(-1) to a maximal of 0. 049 min(-1) and a net release of 30%. This osmosensitive efflux was inhibited by Ba(2+) (0.028 min(-1)), quinidine (0.024 min(-1)), and charybdotoxin (0.040 min(-1)), but was unaffected by TEA, 4-AP, or apamin. Removal of external Ca2+ from the hyposmotic medium increased (86)Rb efflux to a maximal rate constant of 0.056 min(-1) and a net release of 38% and caused a delay of inactivation. These changes were due to the overlaping of an efflux activated by Ca2+ removal in isosmotic medium. This isosmotic 86Rb efflux was unaffected by TEA or 4-AP, reduced by verapamil, and abolished by Ba2+, nitrendipine, and Mg2+. With the swelling-induced [Ca2+]i rise suppressed by ethyleneglycoltetraacetic acid-acetoxy-methyl ester (EGTA-AM), hyposmotic (86)Rb was 30% reduced. The Ca2+ entry blockers Cd2+, Ni2+, La3+, and Gd3+ did not affect (86)Rb efflux. A 40% decrease observed with verapamil and nitrendipine was found unrelated to Ca2+, because these agents did not affect the [Ca2+]i rise and the inhibition persisted in the absence of external Ca2+. The phospholipase C blocker U-73122 did not affect [Ca2+]i nor (86)Rb efflux. Blockers of Ca2+/calmodulin W7 and KN-93 decreased (86)Rb efflux to the same extent as EGTA-AM. Ionomycin markedly potentiated (86)Rb release in hyposmotic conditions only when [Ca2+]i was raised to about 1 microM, suggesting the implication of maxi-K+ channels at this [Ca2+]i threshold, which nonetheless, was not attained during hyposmotic swelling. It is concluded that (86)Rb efflux in cerebellar astrocytes is largely (70%) Ca2+-independent and the Ca2+-dependent fraction is sustained essentially by Ca2+ released from the endoplasmic reticulum and mediated by a mechanism involving Ca2+/calmodulin.
Asunto(s)
Astrocitos/efectos de los fármacos , Calcio/farmacología , Cerebelo/efectos de los fármacos , Potasio/metabolismo , Animales , Astrocitos/metabolismo , Células Cultivadas , Cerebelo/citología , Cerebelo/metabolismo , Concentración Osmolar , Ratas , Radioisótopos de RubidioRESUMEN
1. The effects of glucose on insulin secretion and 86Rb efflux from isolated rat islets were studied at six different times during a 24-h period (00.00, 04.00, 08.00, 12.00, 16.00 and 20.00 h). 2. In the absence of glucose and in the presence of substimulatory concentrations (2.8 mmol/L) of the sugar, insulin secretion did not vary with the time of day. At a glucose concentration of 5.6 mmol/L the stimulated insulin secretion was greater than basal levels only at 20.00 h. 3. At a higher sugar concentration (8.3 mmol/L) the increase in insulin secretion and the reduction in 86Rb efflux rate were more marked during the dark period. No effect of the time of day on insulin secretion was observed at glucose concentrations above 8.3 mmol/L (except in 27.7 mmol/L). 4. The time of day appears to affect insulin secretion mainly at glucose concentrations close to physiological values (5.6-8.3 mmol/L). 5. This result agrees with the ability of physiological amounts of glucose to alter the 86Rb-permeability of pancreatic B cells at the same time intervals.
Asunto(s)
Ritmo Circadiano , Insulina/metabolismo , Islotes Pancreáticos/metabolismo , Potasio/metabolismo , Animales , Cloruros/metabolismo , Glucosa/metabolismo , Técnicas In Vitro , Secreción de Insulina , Masculino , Permeabilidad , Ratas , Ratas Wistar , Rubidio/metabolismo , Radioisótopos de RubidioRESUMEN
Islets isolated from rats fed a lipid-enriched diet have shown an impairment of insulin secretion, but there is no available data comparing the effect of diet containing different dietary fat. This may be important in preventing or facilitating the establishment of diabetes. In this study, the effect of diets enriched (10%) with different fatty acids on insulin secretion by isolated pancreatic islets was investigated. The sources of the fatty acids tested were: saturated long chain from animal fat (AF), polyunsaturated from soybean oil (SO), and monounsaturated from olive oil (OL). The results were compared with those from rats receiving a diet enriched (10%) with a balanced mixture of fatty acids (the same proportion of AF, SO, and OL). The effect of fat-rich diets on insulin release was tested in vivo by giving a glucose load (glucose tolerance test-GTT) and in vitro in perfused islets. The mechanism involved was also examined by measuring 45Ca2+ and 86Rb+ fluxes, GLUT-2 content, and glucose oxidation in isolated islets. A significant increase of insulin secretion and glucose oxidation without any alteration of the ionic movements were detected in islets from SO and OL rats. GLUT-2 content was increased in islets of the OL group but diminished in AF rats. The results led us to postulate that soybean and olive oils may increase the response of insulin secretion to glucose stimulus in pancreatic islets.
Asunto(s)
Grasas de la Dieta/farmacología , Glucosa/farmacología , Insulina/metabolismo , Islotes Pancreáticos/metabolismo , Aceites de Plantas/farmacología , Aceite de Soja/farmacología , Animales , Glucemia/metabolismo , Western Blotting , Dieta , Prueba de Tolerancia a la Glucosa , Transportador de Glucosa de Tipo 2 , Técnicas In Vitro , Insulina/sangre , Secreción de Insulina , Islotes Pancreáticos/efectos de los fármacos , Masculino , Proteínas de Transporte de Monosacáridos/metabolismo , Aceite de Oliva , Oxidación-Reducción , Ratas , Radioisótopos de RubidioRESUMEN
The effects of the muscarinic agonist oxotremorine-m (Oxo-m) on 45Ca and 86Rb fluxes, insulin secretion, cytoplasmic Ca2+ concentration ([Ca2+]i) and membrane potential in pancreatic B-cells were studied. Oxo-m (40-200 microM) increased the [Ca2+]i by about 250 nM, irrespective of the glucose concentration present in the medium (2.8-22 mM). This effect was reduced by 50% upon the addition of EGTA. Oxo-m (50 microM) increased the 45Ca efflux from islets perifused in the absence or presence of [Ca2+]o, although under the former condition this efflux was transient. The difference between effluxes measured in the absence and presence of [Ca2+]o represents the sustained second component, which presumably reflects Ca2+ influx. In both the absence and presence of 11.2 mM glucose. Oxo-m (50 microM) transiently increased 86Rb efflux. In the presence of glucose, Oxo-m provoked a transient polarization of the B-cell membrane associated with an increase in the K+ permeability values. K+ permeability returned to basal values (no Oxo-m) after 1-2 min. These results indicate that the initial phase of Oxo-m-induced insulin secretion depends partially on intracellular Ca2+ release, and that the sustained enhancement of release depends on Ca2+ influx. The participation of a calcium release-activated current (ICRAC) is proposed to explain the sustained small changes in membrane potential.
Asunto(s)
Calcio/metabolismo , Islotes Pancreáticos/metabolismo , Agonistas Muscarínicos/farmacología , Oxotremorina/farmacología , Potasio/metabolismo , Animales , Radioisótopos de Calcio , Permeabilidad de la Membrana Celular/efectos de los fármacos , Ácido Egtácico/farmacología , Electrofisiología , Glucosa/metabolismo , Glucosa/farmacología , Técnicas In Vitro , Insulina/metabolismo , Islotes Pancreáticos/efectos de los fármacos , Ratones , Ratas , Radioisótopos de RubidioRESUMEN
Previous study has shown that insulin secretion in response to a glucose stimulus (16.7 mM) is reduced in islets isolated from Walker 256 tumor-bearing rats compared with controls. The ultrastructure, 45Ca2+ and 86Rb+ fractional outflow rate, phosphoinositide hydrolysis, and [U-14C]glucose decarboxylation were examined in islets isolated from tumor-bearing and control rats. The general morphological features of the islets from the control and experimental groups were very similar. The 86Rb+ fractional outflow rate was not changed, whereas the 45Ca2+ fractional outflow rate, [U-14C]glucose decarboxylation, and phosphoinositide metabolism were markedly reduced in islets from tumor-bearing rats. The changes in 45Ca2+ fractional outflow rate in islets from tumor-bearing rats were not due to impaired functioning of voltage-dependent calcium channels. By perifusing the islets in the presence of high potassium concentration, evidence was obtained that phospholipase C from islets from tumor-bearing rats reduced response to calcium. To further examine the mechanism involved in the impairment of insulin secretion by islets from tumor-bearing rats, islets isolated from normal rats were perifused after preincubation in the presence of serum from tumor-bearing rats. The results suggest that a thermolabile circulating factor is partially responsible for the changes described in islets isolated from Walker 256 tumor-bearing rats.
Asunto(s)
Carcinoma 256 de Walker/metabolismo , Insulina/metabolismo , Islotes Pancreáticos/metabolismo , Neoplasias Experimentales/metabolismo , Animales , Radioisótopos de Calcio , Carcinoma 256 de Walker/patología , Secreción de Insulina , Transporte Iónico , Islotes Pancreáticos/patología , Masculino , Neoplasias Experimentales/patología , Ratas , Radioisótopos de RubidioRESUMEN
Highly purified Tityustoxin V (TsTX-V), an alpha-toxin isolated from the venom of the Brazilian scorpion Tityus serrulatus, was obtained by ion exchange chromatography on carboxymethylcellulose-52. It was shown to be homogeneous by reverse phase high performance liquid chromatography, N-terminal sequencing (first 39 residues) of the reduced and alkylated protein and by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate and tricine. Following enzymatic digestion, the complete amino acid sequence (64 residues) was determined. The sequence showed higher homology with the toxins from the venoms of the North African than with those of the North and South American scorpions. Using the rate of 86Rb+ release from depolarized rat pancreatic beta-cells as a measure of K+ permeability changes, TsTX-V (5.6 micrograms/ml) was found to increase by 2.0-2.4-fold the rate of marker outflow in the presence of 8.3 mM glucose. This effect was persistent and slowly reversible, showing similarity to that induced by 100 microM veratridine, an agent that increases the open period of Na+ channels, delaying their inactivation. It is suggested that, by extending the depolarized period, TsTX-V indirectly affects beta-cell voltage-dependent K+ channels, thus increasing K+ permeability.