Relation of Extracellular to Intracellular Potential Records from Single Cardiac Muscle Fibres

Abstract

IN the atrial muscle of the heart the rate of depolarization (70–100 V./sec. at 30° C.) is so much more rapid than that of repolarization (less than 1.0 V./sec.) that the two events cannot be confused, and a comparison may be made between records obtained from the inside and outside of a single fibre during the depolarization phase only¹. Pairs of isolated rabbit atria were mounted horizontally in oxygenated fluid and made to beat at constant frequency in response to electrical stimuli applied to the tip of the left atrium. Contractions were measured with a transducer, and action potentials from the left and right atria were recorded with pairs of small bipolar external electrodes, from which conduction velocity was calculated. Glass microelectrodes, filled with potassium chloride, with tips less than 0.5µ across and resistances of 10–30 MΩ, were introduced under visual control into single fibres on the endocardial surface by a manipulator which could be moved smoothly over distances as small as 2µ