Abstract
The application of the capillary ultramicroelectrode method to single cardiac fibers in situ was devised. The mean value of 10 selected data of the tortoise ventricular fibers was 66mV (54-86mV) in the resting potential, 76mV (60-100mV) in the action potential, 10mV (1-36mV) in the overshoot. The duration of the action potential varied from 0.6 to 1.4 seconds. The action potential of the auricular fibers is narrow in its shape. The plateau of the repolarization is lost to some extent and declines more rapidly. The mean value of 10 selected data was 56mV (50-63mV) in the resting potential, 65mV (55-90mV) in the action potential, 9mV (2-30mV) in the overshoot. Its duration varied from 0.4 to 0.7 seconds. No significant difference could be found between the data of the left and right atrium.
The curves of the resting and action potential obtained could be clearly differentiated from those by artefact such as by mechanical movement of heart muscle contractions. As for their magnitude, however, the influence by possible injury of cell membranes due to insertion of the microelectrodes could not be excluded definitely. Apart from the absolute value of their magnitude thus obtained, there is possibility at least to utilize timing of the curves of the action potential as a new indicatory method of the electrical activity of the heart.
