Ion-mediated resistance to osmotic changes of ram spermatozoa: The role ofamiloride and ouabain

The aim of this study was to evaluate whether the Na+/K+ and Na+/H+ exchang e can maintain the function of fresh ram spermatozoa. We analyzed the quali ty parameters of spermatozoa fi om fresh ram ejaculates incubated in iso- ( about 300 mOsm), hypo- (about 100 mOsm) and hyperosmotic (about 900 mOsm) m edia in the presence of ouabain, a specific inhibitor of the Na+/K+ ATP-ase or amiloride, a specific inhibitor of the Na+/H+ antiporter. Ouabain incre ased the percentage of morphologically altered acrosomes in isoosmotic medi a (from about 10% to 15% in control to about 30% with 10(-4)M ouabain) and decreased the percentage of total motility (from about 80% in control to ab out 50% to 55% with 10(-4)M ouabain). Ouabain decreased the mean linearity component of motility and decreased the fiequency of head displacement. The addition of ouabain increased the percentage of altered acrosomes in the h ypo- and hyperosmotic media, although it did not modify viability in either media. Ouabain also increased the percentage of swollen tails in the hypoo smotic medium at higher concentrations of the inhibitor. Amiloride increase d the percentage of altered acrosomes in all media although its effect was less intense than that of ouabain. In isoosmotic media total motility was d ecreased from about 80% in control to about 65% with 10(-4)M amiloride. Mot ile spermatozoa incubated with amiloride showed a clear decrease of mean ve locity and mean linearity and increased frequency of head displacement. In the hyperosmotic medium, adding amiloride decreased the percentage of viabi lity and altered tails at concentrations as low as 10(-6) to 10(-5)M. Our r esults indicate that the active mechanisms which control Na+ transport play a significant role in the maintenance of function in ram spermatozoa subje cted to different osmotic environments. These mechanisms may be important i n maintaining ram sperm function both "in vivo" and "in vitro". (C) 2000 by Elsevier Science Inc.