Our long range goal is to understand the signal transduction mechanisms that mediate induction of acrosomal exocytosis in sperm by the egg's zona pellucida. The current phase of this research focuses on the identification of zona pellucida-regulated ion transport proteins in mouse sperm. To this end, we will apply fluorescent indicator dye and radioreceptor binding methods to sperm populations and to single cells. These studies will be carried out in the mouse, a well characterized model system of gamete interaction. 1) The role of sperm membrane potential in regulating acrosome reactions will be characterized. Preliminary data indicates that zonae pellucidae produce depolarizations of sperm membrane potential. The ionic basis of resting potential and of zona pellucida-promoted alterations in membrane potential will be determined. Additional studies will examine the effects of capacitation on membrane potential in the absence and in the presence of zonae pellucidae. 2) The role of voltage-dependent Ca 2+ channels in mediating zona pellucida-induced acrosome reaction will be characterized. The objective is to determine the variety of Ca 2 + channel types present in sperm and the mechanisms whereby channels are activated during sperm capacitation and interaction with the zonae pellucidae. In addition, preliminary data demonstrates that the dihydropyridine-sensitive class of voltage-sensitive Ca 2 + channels function during induction of exocytosis. These channels will be characterized and their role in exocytosis determined. 3) Sperm intracellular pH is an essential mediator of zona pellucida-induced exocytosis. The H+-transport pathways activated by zonae pellucidae will be characterized and the relationship of these H+-transporters to other ionic mediators (membrane potential internal calcium) will be determined.