THE MONOPHASIC ACTION POTENTIAL CURVE OF TORTOISE VENTRICULAR MUSCLE

Abstract

This paper describes the early results obtained in a study of the electrical changes occurring at the point of stimulation. The action potentials were recorded by a recently designed capillary electrometer used in combination with a one-panel thermionic vacuum tube amplifier. Proper balancing of the stimulating circuit made possible the use of the cathodal stimulating electrode as one of the lead-off electrodes. No purely monophasic records could be obtained by direct methods. By using purely diphasic records obtained from a strip in which tissue condition under the 2 electrodes was similar, it was possible to reconstruct the monophasic action potential changes occurring at the site of stimulation. Such reconstruction gives a curve of negativity rising promptly and rapidly after stimulation, continuing negativity through the period of contraction, and a return toward the base line approximately during the mechanical phase of relaxation. The form of the monophasic curve, especially of the falling phase, shows variations according to the condition of the tissue. The R- and T-waves recorded from strip preparations can only be regarded as the diphasic expressions of such monophasic changes.