Motility initiation of quiescent spermatozoa from rat caudal epididymis: effects of pH, viscosity, osmolality and inhibitors

Non-motile spermatozoa freshly extruded from the rat caudal epididymis can be initiated to full motility immediately after diluting with 0.9% NaCl. The motility initiation was dependent on the pH, viscosity and osmolality of diluent. Diluent with pH 4 to 8 could optimally initiate the motility. Osmolality of most diluents suitable for the initiation was between 130 to 600 mOsm/kg. The motility initiation was inhibited by Hg2+ greater than Cu2+ greater than Cd2+, chlorpromazine, Triton X-100 and SDS. The following compounds showed essentially no inhibitory effect: EGTA, chlortetracycline, calcein, ruthenium red, phloridzin, myo-inositol and carnitine. The findings suggested that spermatozoa were kept in quiescence in the cauda epididymis not by the pH, osmolality, viscosity, myo-inositol, carnitine, Ca2+ or K+ of the caudal epididymal fluid. It was also suggested that motility initiation did not involve Ca2+, calmodulin and transport of Ca2+ or glucose across sperm membrane.