Studies of the mechanism of the electrical polyspermy block using voltage clamp during cross-species fertilization.

Abstract

Prevention of polyspermic fertilization in sea urchins and the worm Urechis involves an electrically mediated fast block. The fertilizing sperm causes a positive shift in the egg''s membrane potential; this fertilization potential prevents additional sperm entries. Since in Urechis the egg membrane potential required to prevent fertilization is more positive than in the sea urchin, whether in a cross-species fertilization the blocking voltage is determined by the species of the egg or by the species of the sperm is tested. With some sea urchin (Strongylocentrotus purpuratus) females, .gtoreq. 90% of the eggs were fertilized by Urechis sperm; a fertilization potential occurred, the fertilization envelope elevated and sometimes decondensing Urechis sperm nuclei were found in the egg cytoplasm. After insemination of sea urchin eggs with Urechis sperm during voltage clamp at +50 mV, fertilization (fertilization envelope elevation) occurred in only 9 of 20 trials; at +20 mV, fertilization occurred in 10 of 10 trials. With the same concentration of sea urchin sperm, fertilization of sea urchin eggs occurred, in only 2 of 10 trials at +20 mV. The blocking voltage for fertilization in these crosses probably is determined by the sperm species, consistent with the hypothesis that the fertilization potential may block the translocation within the egg membrane of a positively charged component of the sperm.