SPERM MEMBRANE-POTENTIAL - HYPERPOLARIZATION DURING CAPACITATION REGULATES ZONA PELLUCIDA-DEPENDENT ACROSOMAL SECRETION

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 (DiSBAC(2)(3)), and from the lipophilic cation, 3,3'-dipropylthiodicarbocyanine iodide (DiSC(3)(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. (C) 1995 Academic Press, Inc.