IONIC REGULATION OF SPERM BEHAVIOR

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Research proposed will investigate basic biochemical mechanisms by which sperm regulate their intracellular pH (pHi) and by which biochemical processes important to fertilization are regulated by pH. Mechanisms of pHi regulation to be investigated include a Na+:H+ exchange which operates at the cell plasma membrane and respiratory acid production by the mitochondria. Intracellular pH is important to the control of two primary processes which prepare both mammalian and invertebrate sperm for fertilization: metabolic activity and the acrosome reaction. Sperm of the sea urchin, S. purpuratus will be used as a simple model system. Experiments will determine if the Na+:H+ exchange is tightly coupled and requires energy, if it is reversible, and if it is selective for Na+. The contribution of the mitochondria will be evaluated by inhibiting respiration and manipulating pHi. Two target areas for regulation by pHi will be explored to extend our understanding of how ionic processes regulate sperm biochemistry. First, relationships between pHi, intracellular Ca++ and cyclic nucleotides will be examined since the latter two intracellular messengers also undergo changes with sperm metabolic activation or the acrosome reaction. Additionally, Na+:K+ ATPase activity will be studied as a function of pHi and related changes. The functions of this enzyme are essential to regulation of cell Na+ and therefore to the Na+:H+ exchange. Na+:H+ ATPase activity also maintains the normal cellular K+ gradient and membrane potential which both collapse upon induction of the acrosome reaction. Understanding of the mechanisms of these ionic alterations will provide specific biological knowledge about sperm function and is relevant to possible development of contraceptive strategies or preservation of sperm viability.