Sperm-activated channels in ascidian oocytes.

Ionic channels activated during fertilization in the ascidian oocyte membrane have been studied using the single-channel recording technique. These channels, which we have called "fertilization channels," have a single-channel conductance of about 400 pS, a reversal potential of about O mV, and an open time of 2-30 msec. The open channel probability is about 0.2 at +20 mV and increases as the membrane is depolarized. The unitary conductance is among the largest hitherto observed in biological membranes.