MODULATIONS BY EXTERNAL PH ON ANODAL BREAK EXCITATION IN RABBIT SINO-ATRIAL NODAL CELLS

Abstract

Effects of extracellular pH on anodal break excitation in rabbit sino-atrial (SA) nodal cells were investigated using the two-microelectrode voltage-clamp technique. The method of anodal break excitation was developed by Weidmann²⁸⁾，and is regarded as a measurement of the activity of the fast Na⁺ channel. Increasing external pH from 7.4 to 8.5 enhanced the maximum rate of depolarization by anodal break excitation，as compared with the values of control (at pH 7.4). In contrast，a decline of pH from 7.4 to 5.5 inhibited the maximum rate of depolarization，accompanied with depression in the activity. Acidification shifted the inactivation curves (h∞) of the fast Na⁺ current in the depolarizing direction，and alkalinization shifted it in the hyperpolarizing direction. These results suggest that proton would modulate the membrane surface charge of the SA nodal cells，resulting in alteration of the gating kinetics of ionic channels.