EFFECT OF HEMOLYSIN PRODUCED BY VIBRIO PARAHAEMOLYTICUS ON MEMBRANE CONDUCTANCE AND MECHANICAL TENSION OF RABBIT MYOCARDIUM

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Abstract
The action mechanisms of hemolysin extracted from V. parahaemolyticus in rabbit S-A [sino-atrial] node and right atrium cells were studied by the single sucrose gap and isometric tension recording methods. Hemolysin caused the membrane to depolarize reversibly without affecting the action potential generating mechanism. Lowering of [Na+]o inhibited membrane depolarization in the presence of hemolysin while the readministration of normal Tyrode solution induced depolarization. Tetrodotoxin (TTX) barely antagonized the depolarizing action of hemolysin but slowed the rate of development of depolarization. This depolarization is apparently primarily due to the increase in conductance to Na which TTX may not block. The dose-response relationship was obtained by measuring a change in membrane resistance. The concentration necessary to yield 50% maximum reduction of the membrane resistance was 7.5 .mu.g/ml. Accumulation of Na within the cell may be responsible for an increase in twitch tension observed during the action of a low concentration of hemolysin. A higher concentration of hemolysin seemed to promote exchange of intracellular Na with extracellular Ca, especially when the Na concentration of the perfusing solution was reduced, and led to stronger contracture.