Membrane ionic conductances during rest and activity in guinea pig atrial muscle

Abstract

Relative membrane resistance measurements were made with 2 microelectrodes in guinea pig atria during normal action potentials and during the action of acetylcholine and epinephrine-One microelectrode was used to record the intracellular potential and the other for injection of constant current pulses during diastole and at various times during the action potential. The contribution of chloride to membrane currents was estimated by measurement of membrane resistances after replacement of chloride by acetylglycine. The apparent membrane resistance increased during the plateau of the atrial action potential in a manner similar to that seen in Purkinje fibers. On the basis of certain reasonable assumptions, calculations of the changes in gNa and gK were carried out resulting in the approximate time courses of these conductances during action potentials. The implications of these measurements for the mechanism of plateau formation were discussed. The previously shown effect of acetylcholine on gK was confirmed in this preparation, and further observations were made as to its mechanism. Epinephrine was shown to increase on K conductance.