Ionic currents responsible for the generation of pace-maker current in the rabbit sino-atrial node.

Publisher Website
Google Scholar
Abstract
The ionic nature of the pace-maker current (.DELTA.Ip, If, Ih) was investigated in rabbit sino-atrial node using a single sucrose-gap voltage-clamp technique. The pace-maker current was activated by hyperpolarizing clamp steps negative to -50 mV and the pace-maker potential was activated by an action potential or a depolarizing clamp step. Neither pace-maker current nor pace-maker potential were altered by addition of tetrodotoxin, but a tetrodotoxin-sensitive channel could be activated in sino-atrial nodal strips following hyperpolarizing clamp steps. Release of depolarizing or hyperpolarizing test clamps was followed by pace-maker potentials, the magnitudes of which were dependent on the test-clamp potential. The m.d.p. (maximum diastolic potential) approached values near EK (equilibrium potential) following depolarizing clamps and near -45 mV following hyperpolarizing clamps. The results suggest that .DELTA.Ip is carried primarily by Na+ and is blocked by Cs+. It is likely that Ca2+ alters the rate of pacing not only through its contribution to the Isi (slow inward current) system, but also through activation of a K+ conductance.