RESUMEN
In frogs, the glossopharyngeal nerve (GL) innervates taste receptors on almost the entire tongue. The mandibular branch (MBF) and palatine branch (PN) of the facial nerve innervate taste receptors on a very small area at the base of the tongue and on the palate, respectively. In the present study, effects of amiloride, an epithelial sodium channel blocker, on the tonic responses of the GL, MBF and PN in frogs to NaCl, LiCl, KCl and CaCl(2) were investigated. In three nerves, amiloride at 0.5 mM, a relatively high concentration, did not affect the responses to 0.15 (concentration just above threshold)-0.5 M NaCl, 0.5 M LiCl and 0.3 M KCl, whereas it almost completely inhibited the response to 1.0 mM CaCl(2). Amiloride may exert an inhibitory action on the response to CaCl(2) by a competitive antagonism between Ca(2+) and a monovalent cation of amiloride, because the response to Ca(2+) is competitively inhibited by other cations such as Na(+) and Mg(2+). The lack of inhibitory effect of amiloride on the responses in the GL, MBF and PN to NaCl suggests that amiloride-sensitive sodium channels in the apical membrane of taste receptor cells are not involved in sodium taste transduction in frogs.
Asunto(s)
Amilorida/farmacología , Rana catesbeiana/fisiología , Sales (Química)/farmacología , Lengua/efectos de los fármacos , Animales , Lengua/inervaciónRESUMEN
Effects of MCC-135 on contraction and relaxation properties and sarcoplasmic reticulum (SR) function were investigated in the failing ventricular muscle due to diabetic cardiomyopathy. Wistar rats were made diabetic by a single injection of streptozotocin (40 mg/kg i.v.). Seven months later, the left ventricular papillary muscle was isolated and isometric tension was measured. The skinned fiber with functional SR preserved was prepared by treatment of the papillary muscle with saponin and used to study SR Ca(2+) uptake, Ca(2+) release, and Ca(2+) leakage. In diabetic rats, developed tension (DT) was decreased, and 80% relaxation time (TR80) and time to peak tension (TTP) were increased compared with normal rats. MCC-135 decreased TR80 and TTP without significant effect on DT in diabetic rats, but not in normal rats. Isoproterenol increased DT, and decreased TTP and TR80 only in normal rats. In diabetic rats, SR Ca(2+) uptake and SR Ca(2+) release were decreased, and SR Ca(2+) leakage was increased compared with normal rats. MCC-135 increased SR Ca(2+) uptake and decreased SR Ca(2+) leakage in diabetic rats, but not in normal rats. SR Ca(2+) release was not affected by MCC-135 both in normal and diabetic rats. The combination of protein kinase A and cAMP increased SR Ca(2+) uptake only in normal rats. These results suggest that MCC-135 has a positive lusitropic effect that might be associated with enhanced Ca(2+) uptake into the SR and reduced Ca(2+) leakage from the SR. MCC-135 appears to be more beneficial in treating the failing myocardium with lusitropic abnormality than cAMP-increasing drugs.
Asunto(s)
Bencenosulfonatos/farmacología , Cardiomiopatías/fisiopatología , Angiopatías Diabéticas/fisiopatología , Corazón/efectos de los fármacos , Corazón/fisiopatología , Piperazinas/farmacología , Retículo Sarcoplasmático/efectos de los fármacos , Animales , Calcio/metabolismo , Proteínas de Unión al Calcio/farmacología , ATPasas Transportadoras de Calcio/metabolismo , Ventrículos Cardíacos/efectos de los fármacos , Ventrículos Cardíacos/fisiopatología , Masculino , Proteínas Musculares/metabolismo , Contracción Miocárdica/efectos de los fármacos , Miocardio/enzimología , Miocardio/ultraestructura , Músculos Papilares/efectos de los fármacos , Ratas , Ratas Wistar , Retículo Sarcoplasmático/enzimologíaRESUMEN
The mechanism by which Helicobacter pylori induces apoptosis remains unclear. In a previous study using biopsy samples, we found a significant correlation between the urease activity of an H. pylori strain and the apoptosis level induced by this strain. Therefore, in this study, we investigated whether urease and/or the ammonia generated by urease can induce apoptosis. Human gastric epithelial cell lines were cocultured with H. pylori, and the levels of apoptosis and ammonia production were measured. The medium was supplemented (or not supplemented) with urea and cytokines. While a large amount of ammonia (>30 mM) accumulated in the coculture containing urease-positive H. pylori and urea, no significant degree of apoptosis occurred. In the presence of tumor necrosis factor alpha (TNF-alpha), however, a marked acceleration of apoptosis was found in this coculture. Such enhancement of apoptosis was also induced by the addition of 4 to 8 mM ammonia to the cell culture without either H. pylori or urea but containing TNF-alpha. These results suggested that ammonia accelerates cytokine-induced apoptosis in gastric epithelial cells, while ammonia or urease molecules alone are unable to induce a significant degree of apoptosis.
Asunto(s)
Amoníaco/farmacología , Apoptosis/efectos de los fármacos , Mucosa Gástrica/patología , Helicobacter pylori/patogenicidad , Factor de Necrosis Tumoral alfa/farmacología , Línea Celular , Técnicas de Cocultivo , Humanos , Concentración de Iones de Hidrógeno , Ureasa/metabolismoRESUMEN
We studied the expression of cell cycle regulators and growth factor-receptor systems in gastric carcinoma in young adults and tried to clarify the specific alterations associated with H. pylori. We studied 33 young patients (18-29 years old, mean age 26.4) with gastric carcinoma. The patients were classified into two groups according to the degree of atrophic gastritis. Then we examined the expression of p53, cripto, cyclin-E, c-met, c-erbB2 and TGF-alpha immunohistochemically and compared the results between the two groups. The results were compared with 66 sex-, tumor histology-, and depth-matched elder controls (36-86 years old, mean age 64.0). H. pylori was judged by Giemsa staining. Seventeen patients had atrophic changes in the corpus (Group A), while 16 showed superficial gastritis or normal mucosa (Group S). All 17 patients of Group A showed H. pylori infection, while the 3 of the 16 members of Group S did not have H. pylori. p53 overexpression was observed more frequently in Group S (88%) than in Group A (41%, p<0.05). In the 3 patients without H. pylori infection, all carcinoma specimens showed p53 overexpression. Overexpression of cyclin-E was detected in 4 patients from Group S. On the other hand, cripto was observed more frequently in Group A than in Group S. No obvious differences were observed in c-erbB2, TGF-alpha and c-met expression. Overall, p53 overexpression was detected more frequently in younger than in older patients, whereas cripto expression was less detected. These results suggest that p53 and cyclin-E may act in an H. pylori-independent or -adjunctive manner for gastric carcinogenesis. Cripto expression might be correlated tightly with H. pylori infection.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Factor de Crecimiento Epidérmico , Sustancias de Crecimiento/metabolismo , Infecciones por Helicobacter/complicaciones , Glicoproteínas de Membrana , Receptores de Factores de Crecimiento/metabolismo , Neoplasias Gástricas/metabolismo , Adolescente , Adulto , Ciclina E/metabolismo , Femenino , Proteínas Ligadas a GPI , Humanos , Inmunohistoquímica , Péptidos y Proteínas de Señalización Intercelular , Masculino , Proteínas de Neoplasias/metabolismo , Proteínas Proto-Oncogénicas c-met/metabolismo , Receptor ErbB-2/metabolismo , Neoplasias Gástricas/microbiología , Neoplasias Gástricas/patología , Factor de Crecimiento Transformador alfa/metabolismo , Proteína p53 Supresora de Tumor/metabolismoRESUMEN
The efficiencies in derivatization of reducing carbohydrates were compared by capillary electrophoresis using maltose as a model with nine monoaminobenzene derivatives by reductive amination in the presence of sodium cyanoborohydride. We found that aminobenzene derivatives substituted at the 3-position showed good reactivity with reducing carbohydrates as expected from the reaction mechanism, although the fluorescence intensities and molar absorptivities of these derivatives were not as high as those of 2- and 4-aminobenzene derivatives. The reagents, 3-aminobenzamide and 3-aminobenzoic acid, which showed the highest reactivity, were applied to the labeling of carbohydrate chains obtained from some sialic acid-containing glycoprotein samples, and also high-mannose and hybrid-type oligosaccharides. Capillary electrophoresis of these labeled carbohydrate chains in an inner surface-modified capillary with (50% phenyl)methylpolysiloxane allowed excellent separation of sialic acid-containing carbohydrate chains derived from fetuin and thyroglobulin as well as high mannose-type and hybrid-type carbohydrates derived from bovine pancreas ribonuclease B, soybean agglutinin and hen ovalbumin. The lower limit of calibration was as low as the 10(-16) mol (injected amount) with helium-cadmium laser induced detection.
Asunto(s)
Aminobenzoatos , Benzamidas , Carbohidratos/análisis , Electroforesis Capilar/métodos , Glicoproteínas/análisis , Indicadores y Reactivos , Rayos Láser , Manosa/análisis , Ácido N-Acetilneuramínico/análisis , Oligosacáridos/análisis , Espectrometría de Fluorescencia , Tiroglobulina/análisis , Transferrina/análisis , alfa-Fetoproteínas/análisis , metaminobenzoatosRESUMEN
To assess the long-term efficacy of a Ca2+ sensitizer MCI-154, 6-[4-(4'-pyridylamino)phenyl]-4,5-dihydro-3(2H)-pyridazinone hydrochloride trihydrate, on chronic heart failure, we studied the effects of the agent on the life span of cardiomyopathic hamsters of the BIO-14.6 strain. At approximately 150 days of age, 210 male hamsters were randomly divided into three groups: MCI-154 0.1 mg kg(-1), day(-1)(MCI-154-low), MCI-154 1 mg kg(-1) day(-1) (MCI-154-high), and control group. The median survival time in control, MCI-154-low and MCI-154-high groups was 227, 243 and 260 days after the start of treatment, respectively. Final survival rate at 284 days in control, MCI-154-low and MCI-154-high groups was 0, 17.1 and 38.6%, respectively. The cumulative survival times in the two MCI-154 treated groups were significantly prolonged in comparison with that in the control group (P < 0.0001). Thus, the present study clearly showed that MCI-154 prolonged the life span of cardiomyopathic hamsters, suggesting that long-term therapy with MCI-154 would be promising in the treatment of congestive heart failure.
Asunto(s)
Calcio/metabolismo , Cardiomiopatías/tratamiento farmacológico , Cardiotónicos/uso terapéutico , Piridazinas/uso terapéutico , Animales , Cardiomiopatías/metabolismo , Cardiomiopatías/mortalidad , Cricetinae , Modelos Animales de Enfermedad , Masculino , MesocricetusRESUMEN
A method for qualitative and quantitative analysis of Fusarium mycotoxins by gas chromatography-mass spectrometry (GC-MS) using cold on-column injection was improved. Eight typical mycotoxins, including deoxynivalenol (DON), 3-acetyldeoxynivalenol (3ADN), fusarenon-X (FX), diacetoxyscirpenol (DAS), 15-monoacetylscirpenol (15MAS), T-2 toxin (T-2), scirpentriol (SCT), and zearalenone (ZEA) were subjected to GC-MS without chemical derivatization by means of the on-column injection technique. Chromatographic separation of the toxins extracted from barley was achieved as a single peak, and the specific EI mass spectra of each toxin were obtained. The fatty acids in the extract that interfere with measurements of the toxins on the gas chromatogram were removed by precipitation as an insoluble metal soap with zinc acetate. Additional clean-up was accomplished using a Bond Elut Florisil cartridge. The quantitative detection limit in barley ranged from 0.1 to 0.5 micrograms/g. The average recoveries of 93.1% for DON, 3ADN, 15MAS, DAS, T-2 and ZEA, and 46.0% for FX and SCT added to barley at the level of 1 microgram/g were obtained.
Asunto(s)
Grano Comestible/química , Fusarium/química , Micotoxinas/análisis , Calibración , Cromatografía de Gases y Espectrometría de Masas , Indicadores y ReactivosRESUMEN
To explore characteristics of the salt taste function of taste receptor cells located on the posterior tongue, we recorded electrophysiological responses from the whole glossopharyngeal nerve in Sprague-Dawley (SD) rats. For all salts, relative response magnitudes increased with increased stimulus concentrations (0.2-2.0 M) of NH4+, K+, and Na+ salts. The order of effectiveness of stimulation for Cl- salts was NH4Cl > KCl > NaCl. For sodium salts, relative response magnitudes were anion dependent. Sodium salts with small anions (NaCl, NaSCN, and NaNO3) had a much stronger stimulating effect than sodium salts with large anion groups (Na2SO4, C2H3O2Na, and C6H11O7Na). The responses of the glossopharyngeal nerve to the Na+ salts of NaCl, C2H3O2Na, and C6H11O7Na were not inhibited by the lingual application of the epithelial sodium transport blocker amiloride. This is in contrast to large amiloride sensitivity of the chorda tympani nerve. Amiloride also failed to inhibit the responses to K+ salts (KCl and KC2H3O2) and to NH4Cl. These results demonstrate that taste receptors innervated by the glossopharyngeal nerve in SD rats lack amiloride sensitivity as observed in the glossopharyngeal nerve of spontaneously hypertensive and Wistar-Kyoto rats. Furthermore, the difference between the small-anion group and the large-anion group of Na+ salts in their effectiveness to produce responses in the glossopharyngeal nerve parallels the effects noted for the anion dependence in the portion of the taste response resistant to amiloride in the chorda tympani nerve. Sodium salts with the smaller anion produced the larger responses in both glossopharyngeal and chorda tympani nerves after amiloride.
Asunto(s)
Amilorida/farmacología , Nervio Glosofaríngeo/efectos de los fármacos , Papilas Gustativas/efectos de los fármacos , Gusto/efectos de los fármacos , Animales , Ratas , Cloruro de Sodio , Transmisión Sináptica/efectos de los fármacos , Umbral Gustativo/efectos de los fármacosRESUMEN
Metal bite-raising splints of 0.5 mm thickness were attached to the upper molar teeth on both sides of the jaw in rabbits. The effects of these splints on masticatory behaviour during the chewing of soft food (bread) by freely moving rabbits were investigated. We recorded electromyograms (EMGs) of the masseter and digastric muscles. The animals exhibited prolongation of the chewing cycle, decreased EMG activity of the masseter muscle and increased EMG activity of the digastric muscle during chewing after introduction of the bite-raising splints. The effects of the splints on the activities of masticatory muscles were abolished by bilateral sectioning of the maxillary and inferior alveolar nerves. It seems likely that afferents from oral sensory receptors were responsible for the changes in masticatory behaviour after the introduction of the occlusal splint.
Asunto(s)
Electromiografía , Músculo Masetero/fisiología , Masticación/fisiología , Músculos del Cuello/fisiología , Ferulas Oclusales , Animales , Aleaciones Dentales , Electrodos Implantados , Encía/inervación , Masculino , Nervio Mandibular/fisiología , Nervio Mandibular/cirugía , Músculo Masetero/inervación , Nervio Maxilar/fisiología , Nervio Maxilar/cirugía , Mucosa Bucal/inervación , Músculos del Cuello/inervación , Neuronas Aferentes/fisiología , Conejos , Factores de TiempoRESUMEN
Single fibers of the frog glossopharyngeal nerve respond to MgCl2 at concentrations exceeding 10 mM. NiCl2 at 1 mM enhanced the Mg2+ response. CaCl2 at 0.5-2 mM induced an inhibition of the Ni(2+)-enhanced response to Mg2+ ions. A quantitative explanation for these results is provided by the hypothesis that Ni2+ ions secondarily affect a magnesium receptor (designated X*Mg) that is responsible for the Mg2+ response and that Ca2+ ions inhibit the Ni(2+)-enhanced response to Mg2+ ions by competing with Mg2+ ions for X*Mg. Double-reciprocal plots of the experimental data indicate that Ni2+ ions do not affect the affinities of X*Mg for both Mg2+ ions (agonist) and Ca2+ ions (competitive antagonist) appreciably, and that Ni2+ ions at 1 mM enhanced the maximal response to Mg2+ ions by 270%. It appears that a magnesium receptor interacts with an Ni(2+)-binding element that is affected by Ni2+ ions and, thus, Ni2+ ions can induce an enhancement of the Mg2+ response.
Asunto(s)
Cloruro de Calcio/farmacología , Nervio Glosofaríngeo/efectos de los fármacos , Cloruro de Magnesio/farmacología , Fibras Nerviosas/efectos de los fármacos , Níquel/farmacología , Animales , Antagonismo de Drogas , Sinergismo Farmacológico , Nervio Glosofaríngeo/fisiología , Técnicas In Vitro , Fibras Nerviosas/fisiología , Rana catesbeianaRESUMEN
Intracellular accumulation of inorganic phosphate (Pi) and intracellular acidosis, which occur in ischemic and hypoxic hearts, reduce the force of contraction by decreasing the responsiveness of contractile system to Ca2+. In the present study we investigated the effects of MCI-154, a Ca2+ sensitizer that can enhance crossbridge interaction, on the decline in maximal Ca2+-activated force by Pi or acidic pH in skinned fiber bundles of guinea pig hearts. MCI-154 can concentration-dependently reverse the depression in maximal Ca2+-activated force (pCa 4.4) by 20 mM Pi, which was not recovered by a higher concentration of Ca2+ ion (pCa 4.0). The effects of MCI-154 were observed even at a concentration (0.01 M) at which the drug has no effect on the pCa 4.4-induced maximal force in the absence of 20 mM Pi when given alone. MCI-154 inhibited the rightward shift of the pCa-tension relationships, with a marked decrease of maximal force produced by 20 mM Pi or acidic pH (decrease in pH from 7.0 to 6.6). MCI-154 also improved the decline in maximal Ca2+-activated force by 20 mM Pi under acidic pH, but the acidosis did not further decrease the effect of 20 mM Pi. Milrinone, a cyclic AMP-dependent phosphodiesterase inhibitor, and pimobendan, another Ca2+ sensitizer, did not improve the Pi-induced contractile failure. These results indicate that the Ca2+ sensitizer MCI-154 could reverse the contractile failure induced by Pi and/or acidic pH in a skinned fiber preparation via modulation of the strong crossbridge reaction with myosin. MCI-154 may be a promising agent for myocardial contractile failure, in which Pi and H+ progressively increase.
Asunto(s)
Calcio/fisiología , Cardiotónicos/farmacología , Corazón/efectos de los fármacos , Contracción Miocárdica/efectos de los fármacos , Fosfatos/farmacología , Piridazinas/farmacología , Animales , Cobayas , Corazón/fisiología , Ventrículos Cardíacos/efectos de los fármacos , Concentración de Iones de Hidrógeno , Técnicas In Vitro , Milrinona , Contracción Miocárdica/fisiología , Piridonas/farmacología , Función VentricularRESUMEN
Two new monoterpene glycosides, kudingosides A and B, were isolated from Ku-Ding-Cha (Ligustrum pedunculare REHD.), together with a known monoterpene glycoside, (S)-lipedoside B-III, and three known phenylethanoid glycosides. Their structures were elucidated by spectroscopic and chemical means. Kudingosides A and B, and (S)-lipedoside B-III inhibited acyl-CoA: cholesterol acyltransferase (ACAT) with IC50 values of 2.70 x 10(-3)M, 2.88 x 10(-3)M, and 2.69 x 10(-4)M, respectively.
Asunto(s)
Medicamentos Herbarios Chinos/farmacología , Inhibidores Enzimáticos/aislamiento & purificación , Glicósidos/aislamiento & purificación , Esterol O-Aciltransferasa/antagonistas & inhibidores , Terpenos/aislamiento & purificación , Monoterpenos Acíclicos , Secuencia de Carbohidratos , Medicamentos Herbarios Chinos/química , Inhibidores Enzimáticos/química , Inhibidores Enzimáticos/farmacología , Glicósidos/química , Glicósidos/farmacología , Cinética , Datos de Secuencia Molecular , Oxidación-Reducción , Espectrofotometría Ultravioleta , Terpenos/química , Terpenos/farmacología , Terpenos/efectos de la radiaciónRESUMEN
The effects of some beta-adrenoceptor antagonists (atenolol, betaxolol, bunitrolol, labetalol, pindolol, and propranolol) on Ca2+ (pCa 5.8)-activated tension development in chemically skinned fibers from canine coronary artery and right ventricular trabeculae were studied. In skinned coronary arteries, Ca(2+)-activated tension development was decreased by betaxolol and propranolol at concentration of more than 10(-5) and 10(-4) M, respectively. The pCa-tension relationships were shifted to the right and down by betaxolol. In contrast, in skinned cardiac muscle Ca(2+)-activated tension development was increased by betaxolol and propranolol at the same range of concentrations as in coronary arteries, with no change in maximum tension. The pCa-tension relation was shifted to the left by betaxolol. Other beta-adrenoceptor antagonists (atenolol, bunitrolol, labetalol, and pindolol) had no effect on Ca(2+)-induced contraction in either muscle type. These results indicate that among beta-adrenoceptor antagonists, only betaxolol and propranolol can directly modulate the Ca2+ sensitivity of myofilaments and have opposite effects on the contractile system in canine cardiac and vascular smooth muscle.
Asunto(s)
Antagonistas Adrenérgicos beta/farmacología , Betaxolol/farmacología , Calcio/farmacología , Proteínas Contráctiles/farmacología , Músculo Liso Vascular/efectos de los fármacos , Propranolol/farmacología , Vasoconstricción/efectos de los fármacos , Animales , Calcio/antagonistas & inhibidores , Vasos Coronarios/efectos de los fármacos , Perros , Femenino , MasculinoRESUMEN
Despite its potential as a key determinant of the functional state of striated muscle, the impact of tropomyosin (Tm) isoform switching on mammalian myofilament activation and regulation in the intact lattice remains unclear. Using a transgenic approach to specifically exchange beta-Tm for the native alpha-Tm in mouse hearts, we have been able to uncover novel functions of Tm isoform switching in the heart. The myofilaments containing beta-Tm demonstrated an increase in the activation of the thin filament by strongly bound cross-bridges, an increase in Ca2+ sensitivity of steady state force, and a decrease in the rightward shift of the Ca2+-force relation induced by cAMP-dependent phosphorylation. Our results are the first to demonstrate the specific effects of Tm isoform switching on mammalian thin filament activation in the intact lattice and suggest an important role for Tm in modulation of myofilament activity by phosphorylation of troponin.
Asunto(s)
Citoesqueleto de Actina/metabolismo , Calcio/metabolismo , Proteínas/metabolismo , Tropomiosina/fisiología , Animales , Ratones , Ratones Transgénicos , Miocardio/metabolismo , FosforilaciónRESUMEN
We investigated the vasorelaxant effects of MCI-154, a cardiotonic agent designed to target thin filaments in cardiac muscles in intact and skinned vessels from guinea pigs. In normal Krebs-Henseleit solution, MCI-154 (10(-7)-10(-4) M) inhibited the contractions induced by angiotensin II, (Ang II), endothelin-1 (ET-1), phenylephrine, and phorbol 12-myristate 13-acetate (PMA) in a concentration-dependent manner in guinea pig aorta. In Ca(2+)-free solutions, ET-1 and PMA caused slowly developing and sustained contractions in guinea pig aorta, whereas phenylephrine and caffeine induced transient contractions due to Ca2+ release from the sarcoplasmic reticulum (SR). MCI-154 (10(-7)-10(-4) M) inhibited the contractile responses to ET-1 and PMA. MCI-154 also reduced the contraction induced by Ca2+ release from phenylehrine- and caffeine-sensitive Ca2+ store sites. On the other hand, the relaxation response to MCI-154 was not affected by the presence of methylene blue, a guanylate cyclase inhibitor or by the removal of endothelial cells. MCI-154 decreased the Ca(2+)-activated tension development in saponin-treated skinned fibers from guinea pig femoral arteries. The effects of MCI-154 were not potentiated in the presence of protein kinase A (PKA), whereas those of cyclic AMP were potentiated, possibly because of lack of protein kinase A. The present experiments demonstrate that MCI-154 inhibits vascular contraction when the contractions are produced by any of three mechanisms: protein kinase C (PKC) activation, Ca2+ mobilization from store sites, or sensitization of contractile elements by Ca2+.
Asunto(s)
Músculo Liso Vascular/efectos de los fármacos , Piridazinas/farmacología , Vasodilatadores/farmacología , Animales , Aorta Torácica/efectos de los fármacos , Cafeína/farmacología , Calcio/metabolismo , Endotelio Vascular/efectos de los fármacos , Arteria Femoral/efectos de los fármacos , Cobayas , Técnicas In Vitro , Masculino , Azul de Metileno/farmacología , Relajación Muscular/efectos de los fármacos , Músculo Liso Vascular/fisiología , Fenilefrina/farmacología , Acetato de Tetradecanoilforbol/farmacología , Vasoconstrictores/farmacologíaRESUMEN
Single water fibers of the frog glossopharyngeal nerve respond to relatively high concentrations of NaCl ( > 80 mM). NiCl2 at 1 mM enhanced the Na+ response and reduced the threshold concentration for NaCl to 20 mM. CaCl2 at 0.5-1 mM induced an inhibition of the Ni2+ -enhanced response to Na+ ions. A quantitative explanations for these results is provided by the hypothesis that Ni2+ ions secondarily affect a sodium receptor or channel (designated XNa*) that is responsible for the Na+ response and that Ca2+ ions inhibit the Ni2+ -enhanced response to Na+ ions by competing with Na+ ions for XNa*. Double-reciprocal plots of the experimental data indicate that the affinity of XNa* for both Na+ ions (agonist) and Ca2+ ions (competitive antagonist) in the presence of 1 mM NiCl2 was five times higher than the previously reported values obtained in the absence of NiCl2 (Kitada, 1991). Ni2+ ions at 1 mM enhanced the maximal response to Na+ ions by 190%. It appears that a sodium receptor (or channel) interacts with a Ni2+ -binding element that is affected by Ni2+ ions and, thus, Ni2+ ions can induce both an increase in the affinity of the sodium receptor for the respective cations and an enhancement of the Na+ response.
Asunto(s)
Calcio/metabolismo , Nervio Glosofaríngeo/efectos de los fármacos , Níquel/farmacología , Sodio , Gusto/efectos de los fármacos , Animales , Nervio Glosofaríngeo/fisiología , Técnicas In Vitro , Potenciales de la Membrana , Níquel/antagonistas & inhibidores , Rana catesbeiana , Gusto/fisiologíaRESUMEN
The effects of betaxolol on Ca(2+)-induced contractions in saponin-treated skinned canine renal arteries were examined. Betaxolol decreased the pCa (-log[Ca2+] M) 5.8-induced contraction at the same concentrations at which the drug relaxed the high K(+)-induced contraction in intact smooth muscles. The pCa-tension relation was shifted to the right and downward by betaxolol. Betaxolol inhibited the increase in Ca(2+)-induced contraction by calmodulin, and this effect of betaxolol was observed even at the concentration that had no effect when given alone. These results suggest that betaxolol decreases the Ca2+ sensitivity of the contractile system in skinned canine renal arteries, presumably by inhibiting calmodulin-mediated contractions.
Asunto(s)
Betaxolol/farmacología , Calcio/farmacología , Arteria Renal/efectos de los fármacos , Vasoconstricción/efectos de los fármacos , Animales , Perros , Relación Dosis-Respuesta a Droga , Femenino , Masculino , Músculo Liso Vascular/efectos de los fármacos , Potasio/farmacologíaRESUMEN
We measured the effects of the benzodiazocine derivative, CGP-48506 (5-methyl-6-phenyl-1,3,5,6-tetrahydro-3,6-methano-1, 5-benzodiazocine-2,4-dione), on contraction of intact myocytes and permeabilized fibers of rat ventricular muscle. CGP-48506 is unique in that it is able to sensitize cardiac myofilaments to Ca2+, but unlike all other agents in this class, it is not an inhibitor of type III phosphodiesterase. When added to isolated intact myocytes, CGP-48506 significantly increased the amplitude of cell shortening with little or no change in the Ca2+ transient, as determined by the fluorescence ratio of fura 2. The late phase of the relation between fura 2 ratio and cell length was shifted to the left in the presence of CGP-48506. CGP-48506 also induced a relatively small decrease in diastolic length. However, compared with the thiadiazinone EMD-57033, CGP-48506 had a much smaller effect on diastolic length at concentrations in which there was a bigger inotropic effect. When added to solutions bathing detergent-extracted (skinned) fiber bundles, CGP-48506 increased maximum force. CGP-48506 also increased submaximal force and shifted the pGa-force relation to the left. However, compared with EMD-57033, there was less of an effect of CGP-48506 on force at relatively high pCa values. CGP-48506 did not alter Ca2+ binding to myofilament troponin C. CGP-48506 was able to reverse inhibition of contraction induced by butanedione monoxime both in intact cells and in skinned fiber bundles. Our results indicate that CGP-48506, like EMD-57033, is a positive inotropic agent working through a direct effect downstream from troponin C. CGP-48506, however, appears to have a unique mechanism resulting in less effect on diastolic function.
Asunto(s)
Citoesqueleto de Actina/efectos de los fármacos , Actinas/metabolismo , Azocinas/farmacología , Cardiotónicos/farmacología , Contracción Miocárdica/efectos de los fármacos , Miosinas/metabolismo , Función Ventricular/efectos de los fármacos , Citoesqueleto de Actina/metabolismo , Animales , Calcio/fisiología , Diacetil/análogos & derivados , Diacetil/farmacología , Perros , Relación Dosis-Respuesta a Droga , Masculino , Miocardio/citología , Miocardio/metabolismo , Concentración Osmolar , Quinolinas/farmacología , Ratas , Ratas Sprague-Dawley , Tiadiazinas/farmacologíaRESUMEN
Fibers of the frog glossopharyngeal nerve that are sensitive to water stimulation also respond to Ca, Mg and Na salts. During stimulation with a salt, the cation and the anion are applied together and the anion could influence the response to the cation. We examined this interaction using single unit recordings at the level of fungiform papilla. Nerve impulses of large amplitude were recorded in response to the stimulation of adjacent papillae with increasing concentrations of various Ca, Mg and Na salts. For a given cation, the elicited spike frequency depended on the anion. For example, the responses of single fibers to Ca2+ concentrations above 0.1 mM were maximal with CaSO4 and minimal with Ca(SCN)2. The rank order of efficiency was CaSO4 > CaCl2 = CaBr2 = Ca(NO3)2 > Ca(SCN)2 for Ca2+ ions at 5 mM. The effects of these anions were reversed for Mg and Na salts, the rank orders being Mg(SCN)2 > Mg(NO3)2 > MgBr2 = MgCl2 > MgSO4, for Mg2+ ions at 200 mM, and NaSCN > NaI > NaNO3 > NaBr > NaCl >> NaF = Na2SO4, for Na+ ions at 500 mM. All these sequences correspond to the lyotropic rank order of the anions. In stimulation by a mixture of Ca and Na salts, which have different rank orders with respect to anions, either the response to Ca2+ ions or the response to Na+ ions could be eliminated as a result of mutual antagonism between Ca2+ and Na+ ions. In this case, the rank order of anions was dependent only on the cation that was able to exert a stimulatory effect in the mixture. Threshold concentrations for Ca, Mg and Na salts are influenced by cationic properties, but not by anionic properties. We hypothesize that anions can modulate the efficacy of cation transduction by binding to a membrane element that interacts with each of the three distinct receptors for Ca2+, Mg2+ and Na+ ions without altering the affinities of these receptors for the respective cations. The present results cannot be interpreted in terms of permeability of the apical membrane to anions and changes in surface potential on the apical membrane. The possibility is discussed that an anion-selective paracellular pathway between taste cells is responsible for the effect of anions on the cation-induced response.
Asunto(s)
Aniones/farmacología , Cationes/farmacología , Nervio Glosofaríngeo/efectos de los fármacos , Animales , Calcio/farmacología , Cloruros/farmacología , Nervio Glosofaríngeo/fisiología , Iones , Magnesio/farmacología , Rana catesbeiana , Sodio/farmacología , Solubilidad , Sulfatos/farmacología , Tiocianatos/farmacologíaRESUMEN
We wished to elucidate the effects of the calcium-sensitizing positive inotropic agent MCI-154 and its combined use with an angiotensin-converting enzyme (ACE) inhibitor enalapril on postischemic contractile dysfunction. Anesthetized dogs underwent a 30-min occlusion of the left anterior descending coronary artery (LAD) followed by 2 h of reperfusion. Regional myocardial segment shortening in the ischemic LAD area was assessed by sonomicrometry. Myocardial segment shortening decreased in response to the LAD occlusion and remained decreased during 2-h reperfusion. The intravenous infusion of MCI-154 (0.1 or 0.3 micrograms/kg/min) initiated 10 min after occlusion and throughout reperfusion significantly improved the recovery of segment shortening. The alleviation of the postischemic contractile dysfunction by MCI-154 was augmented when the animals were treated with a bous injection of enalapril (0.3 mg/kg) 15 min before ischemia followed by an infusion of the drug (0.003 mg/kg/min). The pretreatment with enalapril alone (0.3 mg/kg plus 0.003 mg/kg/min or 1 mg/kg plus 0.01 mg/kg/min) did not alleviate the postichemic dysfunction, however, although it decreased systemic blood pressure (BP). Ischemic bed size, myocardial necrosis (by triphenyltetrazolium chloride staining), and collateral blood flow (by colored microspheres) were similar in all experimental groups. These results indicate that MCI-154 improves the postischemic contractile function of dog heart, whereas enalapril fails to improve it. ACE inhibitors may also augment the efficacy of cardiotonics on postischemic dysfunction.