RESUMEN
BACKGROUND: Neonatal adrenal hemorrhage is a relatively uncommon condition (0.2-0.55%). Various risk factors have been reported in addition to birth asphyxia, such as sepsis, coagulation disorders, traumatic delivery, and perinatal injuries. Adrenal hemorrhage usually affects the right adrenal gland (about 70% of cases) while it involves the bilateral adrenal gland only in 10% of cases. In most cases, the event is asymptomatic but, in others, it may be so devastating to determine death by bleeding or adrenal insufficiency. CASE PRESENTATION: A case of bilateral neonatal adrenal hemorrhage, with adrenal insufficiency, but with no important risk factors and favorable evolution in a male infant. CONCLUSIONS: This case emphasizes the importance of keeping a non-interventional attitude, avoiding early surgery but carrying out a serial sonographic follow-up. Serial ultrasound monitoring is the most reliable approach during conservative management.
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Enfermedades de las Glándulas Suprarrenales/diagnóstico , Enfermedades de las Glándulas Suprarrenales/etiología , Hemorragia/diagnóstico , Hemorragia/etiología , Humanos , Recién Nacido , Masculino , Factores de Riesgo , UltrasonografíaRESUMEN
BACKGROUND: Keratinous or epidermoid cysts (ECs) are encapsulated lesions lined by squamous cell epithelium. They comprise approximately 1% of intracranial lesions. Contrary to dermoid cysts, they lack dermal elements such as sebaceous or apocrine glands and hair follicles. The sellar region is the second most common intracranial site following the cerebellopontine angle. Here, we report a case of EC in a patient who complained of endocrine disturbances. We also performed a systematic review on previously published cases to analyze clinical and radiological characteristics and report the treatment outcomes of suprasellar ECs. CASE DESCRIPTION: A 42-year-old woman presented with a one-year history of amenorrhea, weight gain, severe headache, and visual disturbances for 6 months. Work-up identified an elevated prolactin level and a temporal field defect of the right eye. Magnetic resonance imaging (MRI) showed a cystic suprasellar lesion pushing on the optic chiasm. She underwent endoscopic trans-sphenoidal surgery, which confirmed a keratinous cyst on histology. Postoperatively, complete resection was confirmed on imaging. She did well although her hospital stay was prolonged due to diabetes insipidus and hypocortisolism. CONCLUSION: Chronic endocrine disturbances can be the presenting complaints of a suprasellar EC, whose T1-weighted MRI appearance can be non-specific, mimicking other differential diagnoses, such as a Rathke's cleft cyst. However, the T2-weighted MRI appearances of ECs are generally hyper-intense and lesions show diffusion restriction. Treatment is surgical and yields good outcomes in most cases reported.
RESUMEN
AIM: The study was undertaken to explore whether shortening of striated muscle during activity is associated with release of bound Ca2+ into the myofibrillar space as has previously been proposed in order to explain the depressant effect of active shortening. METHODS: The experiments were carried out on single muscle fibres isolated from the anterior tibialis muscle of Rana temporaria. The fibres were loaded with the calcium sensitive indicator Fluo-3. The fibres, stimulated to produce a partially fused isometric tetanus, were subjected to a shortening ramp or, alternatively, to a stretch ramp during activity while force, fibre length, sarcomere length and the Fluo-3 signal were recorded. RESULTS: A shortening ramp performed during a partially fused tetanus caused an increase in the myofibrillar free calcium concentration and produced, simultaneously, a decrease in active force. The isometric force recovered gradually after the shortening ramp, while the intracellular Ca2+ concentration stayed above the control level during the remainder of the stimulation period. A stretch ramp applied during a partially fused tetanus caused a considerably smaller change in the myofibrillar Ca2+ concentration. CONCLUSION: The results provide evidence that the myosin cross-bridges interact with the calcium binding sites on the thin filaments during active shortening, causing sustained release of calcium and reduced contractile strength.
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Calcio/metabolismo , Contracción Muscular/fisiología , Músculo Esquelético/fisiología , Miofibrillas/fisiología , Animales , Estimulación Eléctrica , Rana temporaria , Sarcómeros/fisiologíaRESUMEN
Corticosteroids may improve haemodynamics and facilitate weaning from catecholamines in septic shock. According to some authors, such effects are only accomplished in the presence of absolute or relative adrenal insufficiency. Consequently, corticosteroids are usually given only to patients that present low blood cortisol values or show an inadequate response to cosyntropin (Synachten test). We report the case of a woman affected by septic shock secondary to pneumonia and dependent on norepinephrine infusion for 26 days, who was weaned from catecholamines with hydrocortisone, 100 mg/day i.v. She exhibited a normal response to Synachten, but corticosteroid therapy was continued because haemodynamics improved promptly. A pharmacological effect was hypothesized; the contemporary increase of platelet, decrease of white blood cells, and decrease of plasma fibrinogen supported this hypothesis.
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Corticoesteroides/uso terapéutico , Hormona Adrenocorticotrópica , Catecolaminas/uso terapéutico , Choque Séptico/tratamiento farmacológico , Anciano , Artroplastia de Reemplazo de Cadera , Catecolaminas/administración & dosificación , Catecolaminas/efectos adversos , Femenino , Hematemesis/complicaciones , Hematemesis/tratamiento farmacológico , Humanos , Norepinefrina/administración & dosificación , Norepinefrina/uso terapéutico , Neumonía/complicaciones , Neumonía/tratamiento farmacológico , Choque Séptico/fisiopatología , Vasoconstrictores/administración & dosificación , Vasoconstrictores/uso terapéuticoRESUMEN
Cytoskeletal F-actin associated with synaptic vesicles and granules plays an important role during Ca(2+)-mediated exocytosis. In the present work, we have used amperometry and confocal fluorescence to study the role of internal Ca(2+) in the rearrangement of F-actin (visualised with phalloidin-Alexa 546) during exocytosis in rat mast cells. The F-actin-depolymerising drug, latrunculin A, and the ryanodine receptor agonists ryanodine and caffeine that, per se did not induce exocytosis, enhanced the exocytotic responses elicited by compound 48/80 (C48/80). They also induced cortical actin depolymerisation in the presence or absence of external Ca(2+). Degranulation induced by C48/80 was accompanied by the formation of a cytoplasmic F-actin network. Depletion of internal Ca(2+) with cyclopiazonic acid inhibited latrunculin potentiation of C48/80-stimulated exocytosis and completely blocked the formation of the cytoplasmic F-actin network. This indicates that the mobilisation of Ca(2+) from ryanodine-sensitive intracellular stores plays an important role in the depolymerisation of the cortical F-actin barrier and possibly in the formation of the internal F-actin network during exocytotic activation of peritoneal mast cells.
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Citoesqueleto de Actina/fisiología , Calcio/metabolismo , Exocitosis/fisiología , Mastocitos/metabolismo , Polímeros/metabolismo , Rianodina/farmacología , Citoesqueleto de Actina/metabolismo , Actinas/efectos de los fármacos , Actinas/metabolismo , Animales , Compuestos Bicíclicos Heterocíclicos con Puentes/farmacología , Cafeína/farmacología , Degranulación de la Célula , Citoplasma/metabolismo , Exocitosis/efectos de los fármacos , Membranas Intracelulares/efectos de los fármacos , Membranas Intracelulares/metabolismo , Masculino , Mastocitos/efectos de los fármacos , Mastocitos/fisiología , Peritoneo/citología , Ratas , Ratas Sprague-Dawley , Tiazolidinas/farmacología , p-Metoxi-N-metilfenetilamina/farmacologíaRESUMEN
Grain protein content is one of the major determinants of the baking and nutritional quality of wheat. It has previously been reported that the ditelosomic line of wheat (Triticum aestivum L.) CSDT7BL, where the short arm of chromosome 7B is missing, shows a lower grain protein concentration than the normal line, but a similar grain yield. In the present paper the growth and nitrogen (N) metabolism of wheat plants cv. Chinese Spring (CS) and its ditelosomic line CSDT7BL were compared. When plants were grown to maturity in pots with different N supplements, the wild-type line showed a higher grain protein concentration and a lower straw N concentration than the ditelosomic line at every N level analysed, suggesting a deficiency in the N remobilization capacity. When 15-d-old plants were grown in a growth cabinet in pots with sand, and supplied with nutrient solutions of different nitrate concentrations, the ditelosomic line showed no differences in N uptake per unit of root dry weight, nitrate reductase activity, nitrate, total N concentration or free amino acid concentration. However, the ditelosomic line showed a decreased capacity to export amino acids in the phloem under high N, independently of the N source. This deficiency was also observed under dark-induced senescence. The diminished export of amino acids to the phloem was principally caused by a decrease in the export of Glu, Asp, and Gln. It is suggested that the decrease in grain protein concentration in the ditelosomic line is a consequence of defective export in the phloem of these amino acids.
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Aminoácidos/metabolismo , Nitrógeno/metabolismo , Proteínas de Plantas/metabolismo , Triticum/metabolismo , Transporte Biológico Activo , Senescencia Celular , Cromosomas , Ambiente Controlado , Nitrato-Reductasa , Nitrato Reductasas/metabolismo , Nitratos/farmacología , Tallos de la Planta/enzimología , Tallos de la Planta/genética , Tallos de la Planta/crecimiento & desarrollo , Tallos de la Planta/metabolismo , Compuestos de Amonio Cuaternario/farmacología , Triticum/enzimología , Triticum/genética , Triticum/crecimiento & desarrollo , Urea/farmacologíaRESUMEN
Mast cells exocytotically release histamine/serotonin in response to different secretagogues. We have used substance P and compound 48/80 to study the Ca++ dependency of serotonin exocytosis from peritoneal mast cells using carbon fiber amperometric techniques. The exocytotic release pattern consists of a burst of events superimposed on a slow, transient, amperometric current baseline increase. Cellular re lease parameters (number, frequency and total charge of amperometric events) and individual event characteristics (charge integral, half width and peak amplitude) were similar for the two secretagogues used. Zero Ca++ conditions greatly reduced, without completely abolishing,cellular release parameters. Cyclopiazonic acid, an inhibitor of the endoplasmatic Ca++ ATPase, reduced the cellular exocytotic capacity and diminished the amplitude of individual exocytotic events more effectively than the 0 Ca++ condition. The cyclopiazonic acid effects occurred in the presence of external Ca++, indicating that this condition is not sufficient for maintaining full exocytotic capacity. The results confirm the importance of intracellular Ca++ for exocytotic activation. For the first time evidence is presented that the integrity of intracellular Ca++ pools determines the amplitude and frequency of individual exocytotic events. Saponin, a non-specific detergent, also induced quantal release similar to that obtained with substance P and compound 48/80. This release was not dependent on extracellular Ca++, but cyclopiazonic acid significantly reduced individual exocytotic release.
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Calcio/fisiología , Exocitosis/fisiología , Mastocitos/fisiología , Animales , Células Cultivadas , Transporte Iónico/fisiología , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
The cellular mechanisms responsible for large miniature currents in some brain synapses remain undefined. In Purkinje cells, we found that large-amplitude miniature inhibitory postsynaptic currents (mIPSCs) were inhibited by ryanodine or by long-term removal of extracellular Ca2+. Two-photon Ca2+ imaging revealed random, ryanodine-sensitive intracellular Ca2+ transients, spatially constrained at putative presynaptic terminals. At high concentration, ryanodine decreased action-potential-evoked rises in intracellular Ca2+. Immuno-localization showed ryanodine receptors in these terminals. Our data suggest that large mIPSCs are multivesicular events regulated by Ca2+ release from ryanodine-sensitive presynaptic Ca2+ stores.
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Señalización del Calcio/fisiología , Calcio/deficiencia , Inhibición Neural/fisiología , Terminales Presinápticos/metabolismo , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Vesículas Sinápticas/metabolismo , Animales , Animales Recién Nacidos , Señalización del Calcio/efectos de los fármacos , Cerebelo/efectos de los fármacos , Cerebelo/metabolismo , Cerebelo/ultraestructura , Espacio Extracelular/efectos de los fármacos , Espacio Extracelular/metabolismo , Interneuronas/efectos de los fármacos , Interneuronas/metabolismo , Interneuronas/ultraestructura , Líquido Intracelular/efectos de los fármacos , Líquido Intracelular/metabolismo , Cinética , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Inhibición Neural/efectos de los fármacos , Terminales Presinápticos/efectos de los fármacos , Terminales Presinápticos/ultraestructura , Ratas , Tiempo de Reacción/efectos de los fármacos , Tiempo de Reacción/fisiología , Rianodina/farmacología , Canal Liberador de Calcio Receptor de Rianodina/efectos de los fármacos , Vesículas Sinápticas/efectos de los fármacos , Vesículas Sinápticas/ultraestructura , Tetrodotoxina/farmacologíaRESUMEN
PURPOSE: To determine the accuracy and reproducibility of ultrasonographic (US) readings of optic disc elevations in patients with papilledema compared with confocal scanning laser ophthalmoscope (CSLO) measurements. METHODS: One randomly selected eye of 22 patients with idiopathic intracranial hypertension (IIH) and a variable degree of optic disc swelling underwent five and three repeated measurements of disc height using high-resolution ultrasonography (Biovision unit; Quantel Medical, Clermont-Ferrand, France) and CSLO (Heidelberg Retina Tomograph [HRT]; Heidelberg Engineering, Heidelberg, Germany), respectively. The same procedure was assessed in 14 subjects with variable degrees of physiologic optic disc cupping. US and HRT measurements from each group were individually compared with each other to estimate the accuracy of US readings in both disc conditions in comparison with HRT data. RESULTS: Ultrasonographic readings were positively correlated with HRT measurements in both swollen (r = 0.62, P: = 0.002) and excavated disc (r = 0.84, P: < 0.0002). The 95% limits of agreement between the instruments were 0.24 +/- 0.59 mm (mean +/- 2 SD) and 0. 05 +/- 0.3 mm for swelling and cupping measurements, respectively. The coefficient of variation was 7.63% and 1.8% for swelling and 7. 93% and 5.91% for cupping, with US and HRT, respectively. CONCLUSIONS: The results indicate that US and CSLO readings are correlated i: both disc swelling and cupping conditions, but to a different extent because of a significant discrepancy in papilledema. US assessment can be considered highly reproducible. Combined US and HRT optic disc analysis may be recommended in papilledema evaluation as long as a better correlation can be demonstrated in further studies.
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Hipertensión Intracraneal/diagnóstico por imagen , Oftalmoscopía/métodos , Disco Óptico/diagnóstico por imagen , Papiledema/diagnóstico por imagen , Adolescente , Adulto , Anciano , Femenino , Humanos , Hipertensión Intracraneal/complicaciones , Masculino , Persona de Mediana Edad , Disco Óptico/patología , Papiledema/etiología , Reproducibilidad de los Resultados , Tomografía , UltrasonografíaRESUMEN
Fluorescence signals from the calcium sensitive dyes Fluo-3 or Rhod-2 were obtained simultaneously with isometric tension in single fibres isolated from the anterior tibialis muscle of Leptodactylus insularis (20-22 degrees C). Fluo-3 fluorescence signals were transformed into [Ca2+]i transients as previously described. Most of the decay phase of single twitch transient is well fitted by a single exponential (tau of about 10 ms), followed by a slower declining component lasting tens of milliseconds. During short periods, 10 to 20 s, of low frequency stimulation, between 0.2 and 5 Hz, the basal [Ca2+]i increased slowly from 0.1 to about 0.4 microM, with only minor changes in the exponentially decaying phase. In fibres poisoned with thapsigargin or cyclopiazonic acid (1-2 microM) the tau of decay of fluorescence or Ca2+ transients of single twitches was very similar to that observed in non-poisoned fibres. Nevertheless, in poisoned fibres challenged with repetitive stimulation. the tau of Ca2+ transients decay increased from about 10 ms to >40 ms, while the basal [Ca2+]i increased from 0.1 to 2 microM. Short rest periods (about 5 min) could reverse these effects, indicating that they were not a direct consequence of SR Ca 2+ -ATPase inhibition. The correlation coefficient between tau of decay and basal [Ca2+]i was >0.8 (P<0.0001). Qualitatively similar results were obtained measuring Rhod-2 fluorescence signals. A lumped, two-compartment model could account for these results. Loading the fibres with EGTA-AM, diminished the effects of prolonged stimulation observed in poisoned fibres. Moreover, we show that the Na+ - Ca2+ exchange mechanism does not participate appreciably in fast Ca2+ removal.
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Calcio/metabolismo , Contracción Isométrica/fisiología , Músculo Esquelético/fisiología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Compuestos de Anilina , Animales , Anuros , Sitios de Unión/fisiología , Tampones (Química) , ATPasas Transportadoras de Calcio/antagonistas & inhibidores , ATPasas Transportadoras de Calcio/metabolismo , Estimulación Eléctrica , Electrofisiología , Inhibidores Enzimáticos/farmacología , Colorantes Fluorescentes , Cinética , Magnesio/metabolismo , Microscopía Fluorescente , Modelos Biológicos , Fibras Musculares Esqueléticas/enzimología , Músculo Esquelético/citología , Parvalbúminas/fisiología , Tiempo de Reacción/fisiología , Sodio/metabolismo , Intercambiador de Sodio-Calcio/metabolismo , Tapsigargina/farmacología , XantenosRESUMEN
A cross-sectional serosurvey for markers of prior Cryptosporidium infection was conducted among homosexual or bisexual males infected with human immunodeficiency virus (HIV); of 262 individuals approached, 236 (90%) agreed to participate. Serological response to two Cryptosporidium antigens was measured using a Western blot assay. The intensity or detection of serological responses to two Cryptosporidium antigens was not associated with CD4 cell counts or tap water consumption. A number of sexual practices were related to increased serological response for only the 27-kDa marker, including having had sex within the past 2 years, having anal sex and having had a larger number of sex partners during the past 2 years. Attending a spa or sauna was related to serological response to both the 27-kDa and 17-kDa markers. Based on these results, activities related to sexual activity appear to be a significant risk factors for prior Cryptosporidium infection.
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Infecciones Oportunistas Relacionadas con el SIDA/epidemiología , Anticuerpos Antiprotozoarios/sangre , Bisexualidad , Criptosporidiosis/epidemiología , Cryptosporidium/inmunología , Homosexualidad Masculina , Infecciones Oportunistas Relacionadas con el SIDA/inmunología , Infecciones Oportunistas Relacionadas con el SIDA/parasitología , Adulto , Animales , Antígenos de Protozoos/inmunología , Western Blotting , Estudios Transversales , Criptosporidiosis/inmunología , Humanos , Masculino , Persona de Mediana Edad , Factores de RiesgoRESUMEN
The effects of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) on force and intracellular Ca2+ transient were studied during isometric twitches and tetanuses in single frog muscle fibers. BAPTA was added to the bathing solution in its permeant AM form (50 and 100 microM). There was no clear correlation between the changes in force and the changes in Ca2+ transient. Thus during twitch stimulation BAPTA did not suppress the Ca2+ transient until the force had been reduced to <50% of its control value. At the same time, the peak myoplasmic free Ca2+ concentration reached during tetanic stimulation was markedly increased, whereas the force was slightly reduced by BAPTA. The effects of BAPTA were not duplicated by using another Ca2+ chelator, EGTA, indicating that BAPTA may act differently as a Ca2+ chelator. Stiffness measurements suggest that the decrease in mechanical performance in the presence of BAPTA is attributable to a reduced number of active cross bridges. The results could mean that BAPTA, under the conditions used, inhibits the binding of Ca2+ to troponin C resulting in a reduced state of activation of the contractile system.
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Calcio/metabolismo , Quelantes/farmacología , Ácido Egtácico/análogos & derivados , Contracción Isométrica/efectos de los fármacos , Fibras Musculares Esqueléticas/fisiología , Músculo Esquelético/fisiología , Animales , Ácido Egtácico/farmacología , Técnicas In Vitro , Cinética , Fibras Musculares Esqueléticas/efectos de los fármacos , Músculo Esquelético/efectos de los fármacos , Rana temporaria , Sarcómeros/efectos de los fármacos , Sarcómeros/fisiología , Factores de TiempoRESUMEN
Cooling increases the twitch force of frog skeletal muscle (Rana temporaria; Rana pipiens), but decreases the twitch force of tropical toad muscle (Leptodactylus insularis). Action potentials and intramembranous charge movement in frog and toad fibers were slowed identically by cooling. Cooling increased the integral of twitch Ca2+ detected by aequorin in frog fibers (1.4-fold), while also decreasing the peak and slowing the rate of decay. Conversely, cooling decreased the integral (0.6-fold) and the peak of twitch Ca2+ in toad fibers, without affecting the rate of decay. The difference in entire Ca2+ transients may account for cold-induced twitch potentiation in frogs and twitch paralysis in toads. In sustained contractions of toad fibers, cooling markedly decreased maximum force caused by: (i) tetanic stimulation, (ii) two-microelectrode voltage clamp steps, (iii) high [K+], or (iv) caffeine. Maximum force in sustained contractions was decreased moderately by cooling frog fibers. Rapid rewarming and simultaneous removal of high [K+] or caffeine during a sustained contraction, caused toad muscle force to rise towards the value corresponding to the warm temperature. This did not occur after removing high [K+] or caffeine from toad fibers kept in the cold. Transmission electron micrographs showed no relevant structural differences. Parvalbumins are thought to promote relaxation of frog muscle in the cold. The unique parvalbumin isoforms in toad muscle apparently lack this property.
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Anuros/fisiología , Contracción Muscular/fisiología , Músculo Esquelético/fisiología , Ranidae/fisiología , Animales , Cafeína/farmacología , Calcio/fisiología , Frío , Estimulación Eléctrica/métodos , Electrofisiología , Técnicas In Vitro , Membranas/fisiología , Microscopía Electrónica , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/ultraestructura , Potasio/farmacología , Rana pipiens/fisiología , Rana temporaria/fisiología , DescansoRESUMEN
pQCT is a method which allows the separate determination of cortical and trabecular bone mineral density in the peripheral skeleton. 21 thalassaemic patients (8 females, 13 males) aged from 10 to 32 years, were examined using pQCT at the ultra distal radius to evaluate SSI (Stress-Strain Index). ALP, serum calcium, hydroxyproline, magnesium, IGF-I, and body surface were determined. The results show a good correlation between cortical BMD and age, concentration of hydroxyproline in urine, serum bone Gla protein, body surface index, bone density of trabecular bone and SSI. Good correlation was found between trabecular bone density and age, IGF-I, BGP and PTH, and between SSI and cortical BMD, age and BSI. The linear relationships between age and cortical and trabecular density show an increase of cortical BMD with age and a decrease of trabecular density with age. The same results were obtained considering trabecular and cortical density versus SSI.
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Densidad Ósea , Calcio/metabolismo , Fósforo/metabolismo , Tomografía Computarizada por Rayos X , Talasemia beta/fisiopatología , Adolescente , Adulto , Envejecimiento , Huesos/fisiopatología , Niño , Femenino , Humanos , Hidroxiprolina/orina , Masculino , Osteocalcina/sangre , Estrés Mecánico , Talasemia beta/diagnóstico por imagen , Talasemia beta/metabolismoRESUMEN
1. Using tight-seal whole-cell recording and digital fluorescence imaging, we studied intracellular calcium (Ca2+i) dynamics in cerebellar basket cells, whose dendrites, axon and presynaptic terminals are coplanar, an optimal configuration for simultaneous optical measurements of all functional domains. 2. In Cs(+)-loaded neurones, depolarizing pulses induced large Ca2+i transients in single axonal varicosities and synaptic terminals, contrasting with much weaker signals between varicosities or in the somato-dendritic domain. 3. Axonal branch points consistently displayed [Ca2+]i rises of similar magnitude and time course to those in axonal terminals and varicosities. 4. In biocytin-filled basket cells, varicosity-like swellings were present along the axon including its branch points. Thus, axonal enlargements are not due to fluorescence-induced cell damage. 5. The spatial heterogeneity of Ca2+i signals was also observed in K(+)-loaded cells upon depolarizing trains, suggesting that this behaviour is an intrinsic property of Ca2+i homeostasis in basket cells. 6. We conclude that depolarization of basket cell axons evokes high local Ca2+i signals in synaptic terminals, en passant varicosities and branch points. While high [Ca2+]i in presynaptic structures presumably triggers transmitter release, Ca2+i transients at branch points may control signal transmission in the axonal arborization.
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Axones/fisiología , Calcio/fisiología , Corteza Cerebelosa/citología , Animales , Axones/química , Canales de Calcio/fisiología , Dendritas/química , Dendritas/fisiología , Procesamiento de Imagen Asistido por Computador , Lisina/análogos & derivados , Potenciales de la Membrana/fisiología , Neuronas/química , Neuronas/fisiología , Neuronas/ultraestructura , Técnicas de Placa-Clamp , Características de la Población , RatasRESUMEN
1. The relationship between force and velocity of shortening was studied during fused tetani of single fibres isolated from the anterior tibialis muscle of Rana temporaria (1.5-3.3 degrees C; sarcomere length, 2.20 microns). Stiffness was measured as the change in force that occurred in response to a 4 kHz length oscillation of the fibre. 2. The results confirmed the existence of two distinct curvatures of the force-velocity relationship located on either side of a breakpoint in the high-force, low-velocity range. Reduction of the isometric force (P0) to 83.4 +/- 1.7% (mean +/- S.E.M., n = 5) of the control value by dantrolene did not affect the relative shape of the force-velocity relationship. The breakpoint between the two curvatures was located at 75.9 +/- 0.9% of P0 and 11.4 +/- 0.6% of maximum velocity of shortening (Vmax) in control Ringer solution and at 75.6 +/- 0.7% of P0 and 12.2 +/- 0.7% of Vmax in the presence of dantrolene. These results provide evidence that the transition between the two curvatures of the force-velocity relationship is primarily related to the speed of shortening, not to the actual force within the fibre. 3. The instantaneous stiffness varied with the speed of shortening forming a biphasic relationship with a breakpoint near 0.15 Vmax and 0.8 P0, respectively. The force/stiffness ratio (probably reflecting the average force per cross-bridge), increased with force during shortening. The increase of the force/stiffness ratio with force was less steep at forces exceeding 0.8 P0 than below this point. 4. A four-state cross-bridge model (described in the Appendix) was used to evaluate the experimental results. The model reproduces with great precision the characteristic features of the force-stiffness-velocity relationships recorded in intact muscle fibres.
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Contracción Isométrica , Fibras Musculares Esqueléticas/fisiología , Músculo Esquelético/fisiología , Sarcómeros/fisiología , Animales , Dantroleno/farmacología , Estimulación Eléctrica , Técnicas In Vitro , Contracción Isométrica/efectos de los fármacos , Cinética , Matemática , Modelos Biológicos , Fibras Musculares Esqueléticas/efectos de los fármacos , Oscilometría , Rana temporaria , Estrés Mecánico , Termodinámica , Factores de TiempoRESUMEN
The protein tau was degraded to distinct products by a DNA-stimulated protease isolated from human leukemia HL-60 cell extracts. The enzyme partially purified by sequential chromatography on GTP-agarose, DEAE-cellulose, and TSK 3000 (0.6 X 60 mm) columns eluted as a 300-450 kDa protein which appeared as 60-90 kDa polypeptides on SDS-PAGE. Protease activity was stimulated by synthetic and natural DNAs and was most active at pH 8.5. Human recombinant tau3 was degraded by the DEAE-cellulose-eluted protease to a 26-kDa and several 14- to 16-kDa peptides. Degradation of tau was partially blocked by preincubation with tubulin, suggesting that the DNA-stimulated cleavage of tau occurred at the carboxyl-terminus, at or near the "tubulin-interactive" domains. The 26-kDa fragment was shown by amino acid sequencing to correspond to the N-terminus of tau whereas sequencing of the 16-kDa fragment yielded YKPVDLSKVT. These results show the existence of a DNA-stimulated protease capable of cleaving tau3 between valine-220 and tyrosine-221 (equivalent to valine 309 and tyrosine-310 of tau4).
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ADN/metabolismo , Endopeptidasas/metabolismo , Tirosina/metabolismo , Valina/metabolismo , Proteínas tau/metabolismo , Secuencia de Aminoácidos , Activación Enzimática , Células HL-60 , Humanos , Hidrólisis , Datos de Secuencia MolecularRESUMEN
Cut twitch muscle fibers, mounted in a triple Vaseline-gap chamber, were used to study the effects of temperature on intramembranous charge movement and, in particular, on the repriming of charge 1 (the intramembranous charge that normally moves in the potential range between -100 and +40 mV). Changing the holding potential from -90 to 0 mV modified the voltage distribution of charge movement but not the maximum movable charge. Temperature changes between 16 and 5 degrees C did not modify the fiber linear capacitance, the maximum nonlinear intramembranous charge, or the voltage distribution of charge 1 and charge 2 (the intramembranous charge moving in the membrane potential range between approximately -4 and -160 mV). We used a pulse protocol designed to study the repriming time course of charge 1, with little contamination from charge 2. The time course of charge movement repriming at 15 degrees C is described by a double exponential with time constants of 4.2 and 25 s. Repriming kinetics were found to be highly temperature dependent, with two rate-limiting steps having Q10 (increase in rate of a process by raising temperature 10 degrees C) values of 1.7 and 7.1 above and below 11.5 degrees C, respectively. This is characteristic of processes with a high energy of activation and could be associated with a conformational change of the voltage sensor or with the interaction between the voltage sensor and the calcium release channel.