ON THE SPONTANEOUS ACTIVITIES OF OYSTER MYOCARDIUM CAUSED BY SEVERAL INORGANIC IONS IN SUCROSE SOLUTION

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Abstract
Action potentials of oyster myocardium recorded with suction electrodes showed a similar pattern to that obtained by the intracellular micro-electrodes and their patterns were comparable to the action potentials of the vertebrate smooth muscles. When sea water was replaced by the isotonic sucrose solution the spontaneous activities eventually ceased, but were restored when the heart was returned to sea water. The activities were also restored when the sucrose solution contained either Na+, K+, Sr++ or Ba++. It was suggested that the ionic mechanisms responsible for the initiation of action potential may not be very specific in oyster myocardium, although Na+ may play a major role in the normal condition. Contrary to the vertebrate smooth muscles, Ca++ inhibited a pacemaker activity of the oyster myocardium, therefore, no spontaneous contractions could be observed in CaCl2-sucrose solution.