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

Membrane potential (V-M) was investigated in mouse and bovine sperm po pulations. V-M was determined from the fluorescence emission of the li pophilic anion, bis(1,3-diethylthiobarbituric acid)trimethine oxonol ( DiSBAC(2)(3)), and from the lipophilic cation, 3,3'-dipropylthiodicarb ocyanine iodide (DiSC(3)(5)). Fluorescent signals were corrected for c ontributions of mitochondrial potentials and apparent V-M values were obtained by calibrations in sperm selectively permeabilized with valin omycin or with gramicidin D. The calculated V-M values of uncapacitate d mouse and bovine sperm were approximately -35 and -30 mV, respective ly. In contrast, capacitated populations of mouse and bovine sperm hav e V-M values of -50 to -60 mV. Membrane hyperpolarization is due in pa rt to an enhanced K+ permeability. The development of zona pellucida-a ctivated signal transducing mechanisms during capacitation is dependen t upon hyperpolarization. It is suggested that V-M alterations regulat e the activation state of sperm, thereby suppressing premature acrosom e reactions in uncapacitated sperm and permitting capacitated sperm to respond to zona pellucida stimuli. (C) 1995 Academic Press, Inc.