Interactions between epididymal secretions and spermatozoa.

The interactions between spermatozoa and epididymal secretions are reviewed with respect to the nature of the interactions, the maturity of the spermatozoa and the environment in which spermatozoa mature. The estimated ionic strength of epididymal fluid is low enough for all peripheral proteins to be in close contact with the membrane. Two sorts of interactions are evident, those dependent on the state of the maturity of the spermatozoa (for example peripheral proteins and some integral proteins) and those independent of it (many integral proteins). For the former, a change in the sperm membrane charge must occur to permit recognition of peripheral proteins and the insertion of secreted charged integral membrane proteins may precede the interaction with more distally secreted products. For integral proteins, partition into the membrane may depend on the composition of the plasma membrane. Changes in the sterol content of particular domains have been documented and an array of lipid-binding proteins secreted by the epididymis may mediate these changes. The dependence of the transfer of lipid-anchored proteins to spermatozoa on membranous vesicles invites reassessment of the situation of spermatozoa within the epididymis and their contact with membranous vesicles and merocrine secretions that may be crucial to promoting physiological changes in spermatozoa.