Electrical characteristics and activation potential of Bufo eggs.

Electrical characteristics and their changes during activation were studied with the microelectrodes on the oocytes and eggs of the toad, Bufo vulgaris formosus Boulenger. In young oocytes, the membrane characteristics had some similarities to those of nerve and muscle, except for a relatively large resistance of 25 K ohmcm.(2) and an absence of the action potential in the former. After maturation, however, the membrane characteristics became entirely different from those of oocytes and other excitable tissues. In the mature eggs the membrane resistance was measured to be as high as 200 K ohmcm.(2), and no specific permeability of the membrane to potassium ions was observable. A slow monophasic change in the membrane potential was recorded in every activation produced by mechanical stimulation, and termed "activation potential." In fresh water, its amplitude was as large as 80 to 90 mv. with an overshoot of about 50 mv. The activation potential might be comparable to the action potential of nerve and muscle, but was fundamentally different in ionic mechanism from the latter, since the former was caused by a marked increase in permeability to chloride ions.