The experiments were carried out on male albino mice (n = 47). The slowest action potentials (dV/dt max 3±1 V/s (n = 27)) were recorded in the area of bifurcation of the sino-auricular(SA) node artery from the side of subendocardium. These cells had the longest spike-APs and the highest velocity of diastolic depolarization (DD). Such APs were determined by us as true pacemaker cells (Fig 1). Cs + (1 mmol) provided the greatest inhibitory effect on the duration and velocity of DD. The frequency of AP generation was reduced from 310±20 to 270±25 pulses per minute. Ivabradine (3 μmol) as an If current blocker slowed the velocity of DD two times. At the same time the frequency of AP generation was reduced by 24 % compared with the control. 4 AP in micromolar concentrations did not affect the action potential configuration of true pacemaker cells. 4 AP (1 mM) increased APD20 2 times and dV / dt 2-3 times, but did not have an effect on the duration and velocity the phase of final repolarization. The blocker of the rapid IKr E 4031 (0.5 mmol) lengthen APD90 and APD 100 by 25-30%. As a result, the frequency of AP generation was reduced by 28% due to elongation of spike-AP by 33% and the DD by 24%. The blocker cromanol 293B (5 mmol ) reduced the frequency of AP by 6-24 % due to lengthed of APD 90 and retardation of the velocity plateau phase by 18 % compared with the control.
There are evidences that the slow outward K + current is involved in generation of APs in cells of the mouse sino-auricular node. It contributes 10-15% to the phase of repolarization. The contribution of the rapid outward K + current is 25-30%, and the current Ito - 15-20%. The rest of the contribution is made by the Ca2 + current L-type.
Supported by projects NO:12-P-4-1054 and NO:12-U-4-1022).