Response of isolated sperm plasma membranes from sea urchin to egg jelly

Abstract

The acrosome reaction in sea urchin sperm is induced by a glycoprotein jelly surrounding the egg and is accompanied by changes in ion permeability of sperm plasma membrane. In an attempt to learn what membrane components are involved in the response to jelly, sperm membrane components were reassembled into artificial membrane and assayed for permeability changes mimicking those that occur in sperm. Jelly in sea water at concentrations that induce the acrosome reaction did not significantly change 45Ca2+ uptake of sonicated unilamellar vesicles made with soybean lipid only (ratio jelly:control uptake = 1.08 .+-. 0.36 SD, n = 21). Experiments with pure lipid planar bilayers made with soybean lipid or a lipid extract from sperm and held at various voltages, also did not reveal substantial permeability changes at comparable jelly concentrations. Thus, jelly by itself does not change the conductance of a pure bilayer. In contrast, significant (P .fwdarw. 0.0005, t test for 2 sample means) 45Ca2+ uptake was observed with vesicles made by cosonicating soybean phospholipids and Stronglylocentrotus purpuratus sperm membranes isolated by the method of Cross (1983) (ratio jelly: control uptake + 1.51 .+-. 0.75, n = 20,16 positive out of 20 experiments). The Ca uptake response of the mixed vesicles was also species-specific; it did not occur with jelly from Arbacia punctulata (ratio Arbacia jelly:control = 1.18 .+-. 0.51; ratio Stronglylocentrotus jelly: control = 1.71 .+-. 0.97, n = 10; P .fwdarw. 0.025, paired t statistic). Vesicles made with soybean lipid and an octyl glucoside extract of sperm membranes also responded to jelly with increased 45Ca2+ uptake. These results indicate the starting conditions to isolate and characterize the sperm membrane components that participate in the egg jelly induced permeability changes.