Effect of current flow on the membrane potential of cardiac muscle.

TLDR: An account of experiments designed to investigate the cardiac action potential by applying suitable pulses of current at various stages in the cardiac cycle is contained.

Abstract: Microcapillaries with an external tip diameter of 0 5p. (Ling & Gerard, 1949) can be inserted into single fibres of the cardiac syncytium and may be used to record resting and action potentials. The technique has so far been applied to the frog ventricle (Woodbury, Hecht & Christopherson, 1951) and to 'false tendons' of the dog and kid heart (Draper & Weidmann, 1951). The conductive system of the kid contains typical Purkinje fibres which are larger in diameter (40-lOOup.) than ordinary heart muscle fibres and which are only slightly contractile. In this preparation it is possible to insert two microelectrodes into the same fibre and to leave them intracellular for many minutes. Polarizing current can be applied through one electrode and the change in membrane potential -resulting from current flow recorded through the other electrode. The present paper contains an account of experiments designed to investigate the cardiac action potential by applying suitable pulses of current at various stages in the cardiac cycle.