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 sperma tozoa and the environment in which spermatozoa mature. The estimated ionic strength of epididymal fluid is low enough for all peripheral proteins to b e in close contact with the membrane. Two sorts of interactions are evident , those dependent on the state of the maturity of the spermatozoa (for exam ple peripheral proteins and some integral proteins) and those independent o f it (many integral proteins). For the former, a change in the sperm membra ne charge must occur to permit recognition of peripheral proteins and the i nsertion of secreted charged integral membrane proteins may precede the int eraction with more distally secreted products. For integral proteins, parti tion 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 media te these changes. The dependence of the transfer of lipid-anchored proteins to spermatozoa on membranous vesicles invites reassessment of the situatio n of spermatozoa within the epididymis and their contact with membranous ve sicles and merocrine secretions that may be crucial to promoting physiologi cal changes in spermatozoa.