ИСТИНА

Diadenosine polyphosphates (DAP) are now considered as a new class of endogenous regulatory cardiotropic compounds. In previous studies DAP were demonstrated to affect cardiac electrical activity and contractility in various animal species including rat. DAP caused a decrease in action potential duration and reduced contractility of rat myocardium. At the same time DAP did not affect repolarizing potassium currents that normally participate in AP repolarization (IK1, IKACh, Ito1, IKur) and had a little effect on L-type calcium current in isolated rat cardiomyocytes. However, in addition to these ionic currents AP duration can be regulated via chloride currents. In the present study the presence of transient inward calcium-dependent chloride current Ito2 has been shown in rat ventricular myocardium and influence of DAP on this current was demonstrated for the first time. Ionic currents were recorded in isolated rat ventricular cardiomyocytes using whole-cell patch clamp method. Action potentials were recorded in isolated preparations of rat right ventricle with sharp glass microelectrodes. In the absence of Na+ and K+ ions and in the presence of potassium current blockers 4-aminopyridine (5×10-3 M) and tetraethylammonium (1,5×10-2 M) transient outward current was present in ventricular myocytes. This current was sensitive to non-selective chloride channels blocker 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS, 10-5 М) and L-type calcium current blocker nifedipine (10-5 M). In the presence of diadenosine tetraphosphate in external solution (Ap4A, 10-4 М) the peak amplitude of current increased by 44,54%. Diadenosine pentaphosphate (Ap5A) and NAD+ failed to produce any significant effects on current density. In isolated preparations of rat ventricular myocardium DIDS (10-5 М) blocked acceleration of repolarization induced by Ap4A. Thus, the effects of Ap4A on cardiac electrical activity in rats are at least partially mediated by its influence on the amplitude of repolarizing chloride current Ito2.