DISTURBANCES OF HEART RHYTHM IN OYSTER

Abstract

Cardiac irregularity found in oyster was studied in relation to interaction between cells or groups of fibers, by means of action potential recording from the muscle fiber of each of the connected half-ventricles. A periodical appearance of abnormal heart rate being mainly due to the difference in rhythm of the 2 half-ventricles was frequently observed. The cardiac rhythm becomes somewhat irregular owing chiefly to change in the shape of the trans-membrane action potential, particularly that in the plateau phase. The heart rate is found to be disturbed very often due to the block of conduction. The rhythm becomes remarkably disordered after some severe treatments. The heart rate is disturbed either transiently or sporadically by a considerably slow rate of the rhythm of the other half-ventricle. The interaction between the 2 halves of the ventricle is complicated. As the result of such interaction, the heart rhythm is frequently disordered. Wenckebach phenomenon is recognized also in the oyster heart and the cause of its formation was discussed. Disorders of heart rhythm are considered to be aroused not only by disorders of impulse formation and disorders of conduction, but also by disturbance of interaction between fibers. In the oyster, arrhythmias involving greatly increased heart rate such as flutter and fibrillation was not to be found.