RESUMEN
Action potential voltage-clamp (APVC) is a technique to visualize the profile of various currents during the cardiac action potential. This review summarizes potential applications and limitations of APVC, the properties of the most important ion currents in nodal, atrial, and ventricular cardiomyocytes. Accordingly, the profiles ("fingerprints") of the major ion currents in canine ventricular myocytes, i.e. in cells of a species having action potential morphology and set of underlying ion currents very similar to those found in the human heart, are discussed in details. The degree of selectivity of various compounds, which is known to be a critical property of drugs used in APVC experiments, is overviewed. Thus the specificity of agents known to block sodium (tetrodotoxin, saxitoxin), potassium (chromanol 293B, HMR 1556, E-4031, dofetilide, sotalol, 4-aminopyridine, BaCl(2)), calcium (nifedipine, nisolpidine, nicardipine, diltiazem, verapamil, gallopamil), and chloride (anthracene-9-carboxylic acid, DIDS) channels, the inhibitor of the sodium-calcium exchanger (SEA0400), and the activator of sodium current (veratridine) are accordingly discussed. Based on a theory explaining how calcium current inhibitors block calcium channels, the structural comparison of the studied substances usually confirmed the results of the literature. Using these predictions, a hypothetical super-selective calcium channel inhibitor structure was designed. APVC is a valuable tool not only for studying the selectivity of the known ion channel blockers, but is also suitable for safety studies to exclude cardiac ion channel actions of any agent under development.
Asunto(s)
Potenciales de Acción , Fármacos Cardiovasculares/farmacología , Canales Iónicos/fisiología , Miocitos Cardíacos/efectos de los fármacos , Animales , Bloqueadores de los Canales de Calcio/farmacología , Perros , Humanos , Canales Iónicos/metabolismo , Técnicas de Placa-Clamp , Bloqueadores de los Canales de Potasio/farmacología , Bloqueadores de los Canales de Sodio/farmacologíaRESUMEN
Receptor-mediated changes in intracellular cyclic AMP concentration play critical role in the autonomic control of the heart, including regulation of a variety of ion channels via mechanisms involving protein kinase A, EPAC, or direct actions on cyclic nucleotide gated ion channels. In case of any ion channel, the actual signal transduction cascade can be identified by using properly modified cAMP derivatives with altered binding and activating properties. In this study we focus to structural modifications of cAMP resulting in specific activator and blocking effects on PKA or EPAC. Involvement of the cAMP-dependent signal transduction pathway in controlling rapid delayed rectifier K(+ ) current was studied in canine ventricular myocytes using these specific cAMP analogues. Adrenergic stimulation increased the density of I(Kr) in canine ventricular cells, which effect was mediated by a PKA-dependent but EPAC-independent pathway. It was also shown that intracellular application of large concentrations of cAMP failed to fully activate PKA comparing to the effect of isoproterenol, forskolin, or PDE-resistant cAMP derivatives. This difference was fully abolished following inhibition of phosphodiesterase by IBMX. These results are in line with the concept of compartmentalized release, action, and degradation of cAMP within signalosomes.
Asunto(s)
AMP Cíclico/análogos & derivados , Animales , Colforsina/farmacología , AMP Cíclico/farmacología , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Canales Catiónicos Regulados por Nucleótidos Cíclicos/metabolismo , Perros , Factores de Intercambio de Guanina Nucleótido/metabolismo , Isoproterenol/farmacología , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Miocitos Cardíacos/efectos de los fármacos , Técnicas de Placa-Clamp , Canales de Potasio de Rectificación Interna/efectos de los fármacos , Canales de Potasio de Rectificación Interna/metabolismo , Transducción de SeñalRESUMEN
Methylxanthines, such as theophylline, have been used to treat cardiorespiratory disorders, whereas caffeine is the most widely consumed psychoactive agent in various soft drinks. Because of the worldwide use of these drugs and the recently synthesized xanthine derivatives, an intensive research on the cardiac actions of these substances is under progress. This review focuses on the molecular mechanisms involved in the actions of xanthine derivatives with special reference to their adenosine receptor antagonistic properties. The main basic and human studies on the action of xanthines on impulse initiation and conduction, as well as the electrophysiological and mechanical activity of the working myocardium will be overviewed. The potential beneficial and harmful actions of the methylxanthines will be discussed in light of the recent experimental and clinical findings. The pharmacological features and clinical observations with adenosine receptor subtype-specific xanthine antagonists are also the subject of this paper. Based on the adenosine receptor-antagonistic activity of these compounds, it can be raised that xanthine derivatives might inhibit the cardioprotective action of endogenous adenosine on various subtypes (A(1), A(2A), A(2B) and A(3)) of adenosine receptors. Adenosine is an important endogenous substance with crucial role in the regulation of cardiac function under physiological and pathological conditions (preconditioning, postconditioning, ischemia/reperfusion injury). Recent clinical studies show that acute administration of caffeine or theophylline can inhibit various types of preconditioning in human subjects. There are no human studies, however, for the cardiovascular actions of long-term administration of these drugs. Upregulation of adenosine receptors and increased effectiveness of adenosine receptor-related cardiovascular functions have been observed after long-lasting treatment with methylxanthines. In addition, there are data indicating that blood adenosine level increases after long-term caffeine administration. Since the salutary actions (and also the adverse reactions) of a number of xanthine derivatives are repeatedly shown, the main goal is the development of novel structures that mimic the actions of the conventional methylxanthines as lead compounds, but their adenosine receptor subtype-specificity is higher, their water solubility is optimal, and the unwanted reactions are minimized.
Asunto(s)
Fármacos Cardiovasculares/química , Xantinas/química , Potenciales de Acción/efectos de los fármacos , Animales , Cafeína/farmacología , Fármacos Cardiovasculares/efectos adversos , Fármacos Cardiovasculares/uso terapéutico , Ensayos Clínicos como Asunto , Cardiopatías/tratamiento farmacológico , Humanos , Antagonistas de Receptores Purinérgicos P1/química , Antagonistas de Receptores Purinérgicos P1/farmacología , Antagonistas de Receptores Purinérgicos P1/uso terapéutico , Receptores Purinérgicos P1/química , Receptores Purinérgicos P1/metabolismo , Xantinas/efectos adversos , Xantinas/uso terapéuticoRESUMEN
Class 3 antiarrhythmic agents exhibit reverse rate-dependent lengthening of the action potential duration (APD), i.e. changes in APD are greater at longer than at shorter cycle lengths. In spite of the several theories developed to explain this reverse rate-dependency, its mechanism has been clarified only recently. The aim of the present study is to elucidate the mechanisms responsible for reverse rate-dependency in mammalian ventricular myocardium. Action potentials were recorded using conventional sharp microelectrodes from human, canine, rabbit, guinea pig, and rat ventricular myocardium in a rate-dependent manner. Rate-dependent drug-effects of various origin were studied using agents known to lengthen or shorten action potentials allowing thus to determine the drug-induced changes in APD as a function of the cycle length. Both drug-induced lengthening and shortening of action potentials displayed reverse rate-dependency in human, canine, and guinea pig preparations, but not in rabbit and rat myocardium. Similar results were obtained when repolarization was modified by injection of inward or outward current pulses in isolated canine cardiomyocytes. In contrast to reverse rate-dependence, drug-induced changes in APD well correlated with baseline APD values (i.e. that measured before the superfusion of drug or injection of current) in all of the preparations studied. Since the net membrane current (I(net)), determined from the action potential waveform at the middle of the plateau, was inversely proportional to APD, and consequently to cycle length, it is concluded that that reverse rate-dependency may simply reflect the inverse relationship linking I(net) to APD. In summary, reverse rate-dependency is an intrinsic property of drug action in the hearts of species showing positive APD - cycle length relationship, including humans. This implies that development of a pure K(+) channel blocking agent without reverse rate-dependent effects is not likely to be successful.
Asunto(s)
Potenciales de Acción/fisiología , Antiarrítmicos/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Antiarrítmicos/química , Perros , Cobayas , Frecuencia Cardíaca/efectos de los fármacos , Frecuencia Cardíaca/fisiología , Ventrículos Cardíacos/efectos de los fármacos , Humanos , Microelectrodos , Miocitos Cardíacos/citología , Miocitos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/fisiología , Bloqueadores de los Canales de Potasio/química , Bloqueadores de los Canales de Potasio/farmacología , Canales de Potasio de Rectificación Interna/antagonistas & inhibidores , Canales de Potasio de Rectificación Interna/metabolismo , Conejos , Ratas , Función Ventricular/efectos de los fármacos , Función Ventricular/fisiologíaRESUMEN
BACKGROUND AND PURPOSE: The contribution of the transient outward potassium current (I(to)) to ventricular repolarization is controversial as it depends on the experimental conditions, the region of myocardium and the species studied. The aim of the present study was therefore to characterize I(to) and estimate its contribution to repolarization reserve in canine ventricular myocardium. EXPERIMENTAL APPROACH: Ion currents were recorded using conventional whole-cell voltage clamp and action potential voltage clamp techniques in canine isolated ventricular cells. Action potentials were recorded from canine ventricular preparations using microelectrodes. The contribution of I(to) to repolarization was studied using 100 µM chromanol 293B in the presence of 0.5 µM HMR 1556, which fully blocks I(Ks). KEY RESULTS: The high concentration of chromanol 293B used effectively suppressed I(to) without affecting other repolarizing K(+) currents (I(K1), I(Kr), I(p)). Action potential clamp experiments revealed a slowly inactivating and a 'late' chromanol-sensitive current component occurring during the action potential plateau. Action potentials were significantly lengthened by chromanol 293B in the presence of HMR 1556. This lengthening effect induced by I(to) inhibition was found to be reverse rate-dependent. It was significantly augmented after additional attenuation of repolarization reserve by 0.1 µM dofetilide and this caused the occurrence of early afterdepolarizations. The results were confirmed by computer simulation. CONCLUSIONS AND IMPLICATIONS: The results indicate that I(to) is involved in regulating repolarization in canine ventricular myocardium and that it contributes significantly to the repolarization reserve. Therefore, blockade of I(to) may enhance pro-arrhythmic risk.
Asunto(s)
Sistema de Conducción Cardíaco/metabolismo , Miocardio/metabolismo , Miocitos Cardíacos/metabolismo , Canales de Potasio/metabolismo , Potenciales de Acción/efectos de los fármacos , Animales , Cromanos/farmacología , Perros , Femenino , Ventrículos Cardíacos/efectos de los fármacos , Ventrículos Cardíacos/metabolismo , Masculino , Miocardio/citología , Miocitos Cardíacos/efectos de los fármacos , Técnicas de Placa-Clamp , Fenetilaminas/farmacología , Bloqueadores de los Canales de Potasio/farmacología , Sulfonamidas/farmacología , Función Ventricular/efectos de los fármacosRESUMEN
This review focuses on the potential role of site- and event-selective adenosinergic drugs in the treatment of cardiovascular diseases. Adenosine is released from the myocardium and vessels in response to various forms of stress and acts on four receptor subtypes (A1, A2A, A2B and A3). Adenosine is an important endogenous substance with important homeostatic activity in the regulation of cardiac function and circulation. Adenosine receptors are also involved in the modulation of various cellular events playing crucial role in physiological and pathological processes of the cardiovascular system. These actions are associated to activation of distinct adenosine receptor subtypes, therefore drugs targeting specific adenosine receptors might be promising therapeutic tools in treatment of several disorders including various forms of cardiac arrhythmia, myocardial ischemia-reperfusion injury, angina pectoris, chronic heart failure, etc. Recently, in addition to subtype-specific adenosine receptor agonists and antagonists, a number of substances that enhance adenosine receptor activation locally at the site where the release of endogenous adenosine is the most intensive have been developed. Thus global actions of adenosine receptor agonists and antagonists, as well as desensitization or down-regulation following chronic administration of these orthosteric compounds can possibly be avoided. We discuss the chemical, pharmacological and clinical features of these compounds: (1) inhibitors of membrane adenosine transporters (NBTI, dipyridamole), (2) inhibitors of adenosine deaminase (coformycin, EHNA), (3) inhibitors of adenosine kinase (tubercidin, aristeromycin), (4) inhibitors of AMP deaminase (GP3269), (5) activators of 5'-nucleotidase (methotrexate), (6) adenosine regulators (acadesine) and (7) allosteric adenosine receptor modulators (PD81723, LUF6000). The development of this type of substances might offer a novel therapeutic approach for treating cardiovascular diseases in the near future.
Asunto(s)
Adenosina/uso terapéutico , Enfermedades Cardiovasculares/tratamiento farmacológico , Adenosina/análogos & derivados , Adenosina/química , Animales , Enfermedades Cardiovasculares/enzimología , Enfermedades Cardiovasculares/metabolismo , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Humanos , Receptores Purinérgicos P1/metabolismo , Relación Estructura-ActividadRESUMEN
BACKGROUND AND PURPOSE: In spite of its widespread clinical application, there is little information on the cellular cardiac effects of the antidiabetic drug rosiglitazone in larger experimental animals. In the present study therefore concentration-dependent effects of rosiglitazone on action potential morphology and the underlying ion currents were studied in dog hearts. EXPERIMENTAL APPROACH: Standard microelectrode techniques, conventional whole cell patch clamp and action potential voltage clamp techniques were applied in enzymatically dispersed ventricular cells from dog hearts. KEY RESULTS: At concentrations ≥10 µM rosiglitazone decreased the amplitude of phase-1 repolarization, reduced the maximum velocity of depolarization and caused depression of the plateau potential. These effects developed rapidly and were readily reversible upon washout. Rosiglitazone suppressed several transmembrane ion currents, concentration-dependently, under conventional voltage clamp conditions and altered their kinetic properties. The EC(50) value for this inhibition was 25.2 ± 2.7 µM for the transient outward K(+) current (I(to)), 72.3 ± 9.3 µM for the rapid delayed rectifier K(+) current (I(Kr)) and 82.5 ± 9.4 µM for the L-type Ca(2+) current (I(Ca) ) with Hill coefficients close to unity. The inward rectifier K(+) current (I(K1)) was not affected by rosiglitazone up to concentrations of 100 µM. Suppression of I(to), I(Kr), and I(Ca) was confirmed also under action potential voltage clamp conditions. CONCLUSIONS AND IMPLICATIONS: Alterations in the densities and kinetic properties of ion currents may carry serious pro-arrhythmic risk in case of overdose with rosiglitazone, especially in patients having multiple cardiovascular risk factors, like elderly diabetic patients.
Asunto(s)
Potenciales de Acción/efectos de los fármacos , Hipoglucemiantes/efectos adversos , Canales Iónicos/fisiología , Células Musculares/efectos de los fármacos , Tiazolidinedionas/efectos adversos , Animales , Canales de Calcio Tipo L/fisiología , Perros , Femenino , Ventrículos Cardíacos/citología , Técnicas In Vitro , Masculino , Células Musculares/fisiología , Técnicas de Placa-Clamp , Canales de Potasio/fisiología , Rosiglitazona , Canales de Sodio/fisiologíaRESUMEN
BACKGROUND AND PURPOSE: While the slow delayed rectifier K(+) current (I(Ks)) is known to be enhanced by the stimulation of ß-adrenoceptors in several mammalian species, phosphorylation-dependent regulation of the rapid delayed rectifier K(+) current (I(Kr)) is controversial. EXPERIMENTAL APPROACH: In the present study, therefore, the effect of isoprenaline (ISO), activators and inhibitors of the protein kinase A (PKA) pathway on I(Kr) and I(Ks) was studied in canine ventricular myocytes using the whole cell patch clamp technique. KEY RESULTS: I (Kr) was significantly increased (by 30-50%) following superfusion with ISO, forskolin or intracellular application of PKA activator cAMP analogues (cAMP, 8-Br-cAMP, 6-Bnz-cAMP). Inhibition of PKA by Rp-8-Br-cAMP had no effect on baseline I(Kr). The stimulating effect of ISO on I(Kr) was completely inhibited by selective ß1-adrenoceptor antagonists (metoprolol and CGP-20712A), by the PKA inhibitor Rp-8-Br-cAMP and by the PKA activator cAMP analogues, but not by the EPAC activator 8-pCPT-2'-O-Me-cAMP. In comparison, I(Ks) was increased threefold by the activation of PKA (by ISO or 8-Br-cAMP), and strongly reduced by the PKA inhibitor Rp-8-Br-cAMP. The ISO-induced enhancement of I(Ks) was decreased by Rp-8-Br-cAMP and completely inhibited by 8-Br-cAMP. CONCLUSIONS AND IMPLICATIONS: The results indicate that the stimulation of ß1-adrenoceptors increases I(Kr), similar to I(Ks), via the activation of PKA in canine ventricular cells.