Analysis of sperm-dependent electrical responses during amphibian fertilization.

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We investigated the changes of ionic permeabilities in egg plasma membrane during normal fertilization on anran (toad) and urodele (newt) amphibians with ionsubstitution, inhibitors of ionic channels, and voltage-clamping. In the fertilization of mature toad eggs, we observed the elicitaiton of a spike-like depolarization potential before the positive platea of fertilization potential that has been descrived previously. This spike-like potential is, like the platea, mediated by increased permeabilty to halides such as Cl^- or I^-. In addition, in the polyspemic fertilization of immature toad oocytes, the same spike-like potential was elicited in response to each sperm entranece. These spike potenial are depends on the penetration of sperm into the egg. On the other hand, there is no pronounced electrical changes during the fertilization of newt eggs, but the egg elicited small hyperpolarizing potentials that corresponded to each sperm entrance. It is not yet clear what ionic channels p … More articiapte to these hyperpolarization. According to this investigation, howerver, we have found that the eggs of amphibians elicit the electrical changes that depend on the sperm entrance.In the cross-fertilization between the toad eggs and the newt sperm, we were not able to find the spike-like potential, but the eggs elicited a gradually-changed hyperpolarization before the positive platea of fertilization potential, that was never observed in the normal fertilization. This hypserpolarization is mediated by mainly an increased permeability of monovalent cations such as Na^+. We were not able to find the condition that the toad sperm can fertilize the newt eggs, but we found that the salamander sperm were able to fertilize the newt eggs. The newt eggs elicited several smal hyperpolarization that corresponded well with each seprm entrance. Overall results indicate that both toad and newt eggs open very different ionic channels depending on the species of sperm that enter the eggs. The ionic channels that meiated these potential changes might be in the sperm plasma membrane and might be provided into the egg plasma membrane during membrane fusion at the fertilization. Less