Sperm membrane potential: Hyperpolarization during capacitation regulates zona pellucida-dependent acrosomal secretion

Abstract

Membrane potential (V(M)) was investigated in mouse and bovine sperm populations. V(M) was determined from the fluorescence emission of the lipophilic anion, bis(1,3-diethylthiobarbituric acid)trimethine oxonol (DiSBAC2(3)), and from the lipophilic cation, 3,3'-dipropylthiodicarbocyanine iodide (DiSC3(5)). Fluorescent signals were corrected for contributions of mitochondrial potentials and apparent V(M) values were obtained by calibrations in sperm selectively permeabilized with valinomycin or with gramicidin D. The calculated V(M) values of uncapacitated mouse and bovine sperm were approximately -35 and -30 mV, respectively. In contrast, capacitated populations of mouse and bovine sperm have V(M) values of -50 to -60 mV. Membrane hyperpolarization is due in part to an enhanced K+ permeability. The development of zona pellucida-activated signal transducing mechanisms during capacitation is dependent upon hyperpolarization. It is suggested that V(M) alterations regulate the activation state of sperm, thereby suppressing premature acrosome reactions in uncapacitated sperm and permitting capacitated sperm to respond to zona pellucida stimuli. © 1995 by Academic Press, Inc.