RESUMEN
1. The relative contributions of the rapid and slow components of the delayed rectifier potassium current (IKr and IKs, respectively) to dog cardiac action potential configuration were compared in ventricular myocytes and in multicellular right ventricular papillary muscle and Purkinje fibre preparations. Whole-cell patch-clamp techniques, conventional microelectrode and in vivo ECG measurements were made at 37C. 2. Action potential duration (APD) was minimally increased (less than 7%) by chromanol 293B (10 microM) and L-735,821 (100 nM), selective blockers of IKs, over a range of pacing cycle lengths (300-5000 ms) in both dog right ventricular papillary muscles and Purkinje fibre strands. D-Sotalol (30 microM) and E-4031 (1 microM), selective blockers of IKr, in the same preparations markedly (20-80%) lengthened APD in a reverse frequency-dependent manner. 3. In vivo ECG recordings in intact anaesthetized dogs indicated no significant chromanol 293B (1 mg kg-1 i.v.) effect on the QTc interval (332.9 +/- 16.1 ms before versus 330.5 +/- 11.2 ms, n = 6, after chromanol 293B), while D-sotalol (1 mg kg-1 i.v.) significantly increased the QTc interval (323.9 +/- 7.3 ms before versus 346.5 +/- 6.4 ms, n = 5, after D-sotalol, P < 0.05). 4. The current density estimated during the normal ventricular muscle action potential (i.e. after a 200 ms square pulse to +30 mV or during a 250 ms long 'action potential-like' test pulse) indicates that substantially more current is conducted through IKr channels than through IKs channels. However, if the duration of the square test pulse or the 'action potential-like' test pulse was lengthened to 500 ms the relative contribution of IKs significantly increased. 5. When APD was pharmacologically prolonged in papillary muscle (1 microM E-4031 and 1 microg ml-1 veratrine), 100 nM L-735,821 and 10 microM chromanol 293B lengthened repolarization substantially by 14.4 +/- 3.4 and 18. 0 +/- 3.4% (n = 8), respectively. 6. We conclude that in this study IKs plays little role in normal dog ventricular muscle and Purkinje fibre action potential repolarization and that IKr is the major source of outward current responsible for initiation of final action potential repolarization. Thus, when APD is abnormally increased, the role of IKs in final repolarization increases to provide an important safety mechanism that reduces arrhythmia risk.
Asunto(s)
Músculos Papilares/fisiología , Canales de Potasio con Entrada de Voltaje , Canales de Potasio/fisiología , Ramos Subendocárdicos/fisiología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Animales , Antiarrítmicos/farmacología , Benzodiazepinas/farmacología , Cromanos/farmacología , Canales de Potasio de Tipo Rectificador Tardío , Perros , Electrofisiología , Femenino , Masculino , Piperidinas/farmacología , Bloqueadores de los Canales de Potasio , Canales de Potasio/efectos de los fármacos , Piridinas/farmacología , Sotalol/farmacología , Sulfonamidas/farmacologíaRESUMEN
The anatomical patterns and frequency of occurrence of congenital coronary anomalies (CCA) in a Central European cohort has not yet been studied. The angiographic data of 7,694 consecutive patients undergoing coronary arteriography at the Albert Szent-Györgyi Medical University, Szeged, Hungary, from 1984 to 1994 were analyzed. CCA were found in 103 patients (1.34% incidence). Ninety-eight of them (95.2%) had anomalies of origin and distribution, and five (4.8%) had coronary artery fistulae. The incidence was the highest for the separate origin of left descending artery and left circumflex from the left sinus of Valsalva (52.42%). Anomalous origin of the left circumflex coronary artery from the right coronary was 8.7% while from the right sinus of Valsalva 18.4%. CCA, which may be associated with potentially serious events, such as ectopic coronary origin from the opposite aortic sinus (1.9%) and single coronary arteries (3.88%), were not frequent. The incidence of CCA in the Central European cohort under study was similar to that of the largest North American study. The anatomic classification presented can be useful from both clinical and surgical standpoints.
Asunto(s)
Anomalías de los Vasos Coronarios/epidemiología , Adulto , Anciano , Estudios de Cohortes , Angiografía Coronaria , Anomalías de los Vasos Coronarios/diagnóstico por imagen , Femenino , Humanos , Hungría/epidemiología , Masculino , Persona de Mediana Edad , Prevalencia , Estudios RetrospectivosRESUMEN
The changes in 32P labeling of phosphoproteins were studied in Langendorff-perfused guinea pig hearts during reversal of the stimulatory effects of isoproterenol. Exposure of the hearts to isoproterenol was associated with significant increases in adenosine 3',5'-cyclic monophosphate (cAMP) levels and in the phosphate incorporation into phospholamban in sarcoplasmic reticulum, the 15-kDa protein in the sarcolemma, and troponin I in the myofibrils. Phospholamban was phosphorylated on serine and threonine residues, both of which are sites for cAMP-dependent and Ca(2+)-calmodulin-dependent protein kinases, respectively. Termination of isoproterenol infusion was associated with reversal of the mechanical effects of isoproterenol stimulation and reversal of the increases in tissue cAMP levels. However, the decreases in cAMP levels correlated only with dephosphorylation of phosphoserine in phospholamban. Dephosphorylation of phosphothreonine in phospholamban, the 15-kDa sarcolemmal protein, and troponin I occurred at a slower rate. These findings suggest that cAMP-dependent phosphorylation of phospholamban (phosphoserine) may play a prominent role during beta-adrenergic stimulation of intact hearts.
Asunto(s)
Corazón/fisiología , Receptores Adrenérgicos beta/fisiología , Secuencia de Aminoácidos , Animales , Proteínas de Unión al Calcio/metabolismo , AMP Cíclico/metabolismo , Femenino , Cobayas , Isoproterenol/farmacología , Datos de Secuencia Molecular , Contracción Miocárdica/efectos de los fármacos , Miofibrillas/metabolismo , Fosfatos/metabolismo , Fosforilación , Fosfoserina/metabolismo , Fosfotreonina/metabolismo , Sarcolema/metabolismo , Retículo Sarcoplasmático/metabolismo , Troponina/metabolismo , Troponina IRESUMEN
The intracellular events and specifically the role of protein kinase C-mediated protein phosphorylation, after alpha-adrenergic receptor stimulation of the heart, are not well understood. We examined the phosphorylation of sarcolemmal, sarcoplasmic reticular, myofibrillar, and cytosolic proteins in perfused beating rabbit hearts on activation of protein kinase C by phenylephrine. Perfusion of rabbit hearts with phenylephrine was associated with a positive inotropic response, which was dose and time dependent. Maximal stimulation (1.54-fold increase in +dP/dt) was obtained with 10 microM phenylephrine at 4 minutes. Examination of the activity levels of protein kinase C in these hearts revealed a redistribution of this activity from the cytosolic to the membranous fraction, suggesting the activation of this enzyme in vivo. Prazosin, an alpha 1-adrenergic antagonist, prevented the increase in the inotropy and the redistribution of protein kinase C activity mediated by phenylephrine. Examination of the degree of phosphorylation of membranous, myofibrillar, and cytosolic proteins revealed that activation of protein kinase C in vivo was associated with increased phosphorylation of a 15-kd sarcolemmal protein and a 28-kd cytosolic protein. There were no increases in the degree of phosphorylation of phospholamban in the sarcoplasmic reticulum and of troponin I, troponin T, and C protein in the myofibrils, although these proteins were found to be substrates for protein kinase C in vitro. These findings provide evidence that protein kinase C is activated in response to alpha-adrenergic stimulation and that activation is associated with increased phosphorylation of a 15-kd sarcolemmal protein and a 28-kd cytosolic protein in the myocardium.
Asunto(s)
Corazón/efectos de los fármacos , Proteínas Musculares/metabolismo , Miocardio/metabolismo , Proteína Quinasa C/metabolismo , Receptores Adrenérgicos alfa/efectos de los fármacos , Animales , Citosol/metabolismo , Activación Enzimática , Técnicas In Vitro , Proteínas de la Membrana/metabolismo , Contracción Miocárdica , Miocardio/enzimología , Perfusión , Fenilefrina/farmacología , Fosforilación , Conejos , Estimulación QuímicaRESUMEN
The incorporation of [32P]Pi into sarcolemmal, sarcoplasmic reticular and myofibrillar proteins was studied in Langendorff-perfused guinea pig hearts treated with the alpha-agonist norepinephrine or with protein kinase C activators (phorbol 12-myristate 13-acetate (PMA) or 1,2-dioctanoylglycerol (D8G]. Norepinephrine was administered in the presence of propranolol and atropine, while the protein kinase C activators (PMA and D8G) were infused in the presence of propranolol, atropine and prazosin. Examination of 32P-incorporation into the various cardiac proteins revealed that there were no significant increases in the degree of phosphorylation of the: (1) 15 kDa sarcolemmal protein; (2) phospholamban in sarcoplasmic reticulum; and (3) troponin I and C protein in the myofibrils. In parallel control studies, stimulation of beating guinea pig hearts by isoproterenol was associated with a 4-5-fold increase in 32P-incorporation into phospholamban and troponin I and about a 2-fold increase in 32P-incorporation into C protein and the 15 kDa sarcolemmal protein. These findings indicate that the major cardiac regulatory phosphoproteins, which have been reported to serve as substrates for protein kinase C in vitro, are not phosphorylated by the same enzyme in perfused, beating guinea pig hearts.
Asunto(s)
Diglicéridos/farmacología , Corazón/efectos de los fármacos , Miocardio/metabolismo , Norepinefrina/farmacología , Forboles/farmacología , Proteína Quinasa C/efectos de los fármacos , Proteínas/metabolismo , Animales , Cobayas , Técnicas In Vitro , Fosforilación , Sarcolema/efectos de los fármacos , Retículo Sarcoplasmático/efectos de los fármacosRESUMEN
STUDY OBJECTIVE: The aim was to determine whether activation of protein kinase C by alpha adrenergic agonists or phorbol esters would be associated with increased phosphorylation of the 15 kDa sarcolemmal protein in guinea pig hearts. DESIGN: Intact, beating guinea pig hearts were perfused with modified Krebs-Henseleit buffer containing [32P]Pi and freeze clamped in a control condition or at the peak of the inotropic response to noradrenaline. Membrane vesicles enriched in sarcolemma were isolated and then subjected to SDS polyacrylamide gel electrophoresis and autoradiography. Phosphorylated proteins were identified and 32P incorporation was quantitated. In some cases, hearts were perfused with phorbol 12-myristate, 13-acetate, or dioctanoyl-glycerol, which are known to be potent activators of protein kinase C. EXPERIMENTAL PREPARATIONS: Whole hearts from 55 anaesthetised guinea pigs weighing 500-600 g were used. MEASUREMENTS AND MAIN RESULTS: Perfusion of guinea pig hearts with noradrenaline resulted in increases in contractility and tissue inositol 1,4,5-triphosphate levels, but there were no increases in the phosphorylation of the 15 kDa sarcolemmal protein observed. Furthermore, perfusion with phorbol 12-myristate, 13-acetate, or dioctanoylglycerol failed to stimulate the phosphorylation of the 15 kDa sarcolemmal protein. CONCLUSIONS: These data indicate that the 15 kDa sarcolemmal protein, which may be phosphorylated by protein kinase C in vitro, is not a substrate for the same enzyme in beating guinea pig hearts.