Sperm-activated currents in ascidian oocytes.

Using patch electrodes and the whole-cell recording technique to study fertilization currents in ascidian oocytes under voltage clamp, this paper shows that between -85 and 0 mV the currents are inward with an initial peak ranging from 50 to 600 pA. Voltages more positive than 0 mV inhibit initiation of the fertilization current, but by allowing the oocyte to return briefly to its resting potential fertilization occurs and fertilization currents are outward at positive potentials. By comparison with previous single-channel work, a fertilizing spermatozoon opens about 300 large-conductance channels with zero reversal potential.