Sodium requirement for capacitation and membrane fusion during the guinea-pig sperm acrosome reaction.
Guinea-pig spermatozoa, incubated in a minimal culture medium (MCM-PL) containing 150 mM-Na+ and no added K+, capacitate within 2 h and respond to added Ca2+ with maximal percentage of acrosome reactions. When spermatozoa, initially capacitated in Medium MCM-PL, were washed and resuspended in saline-based media, the motile spermatozoa showed acrosome reactions only in response to added Ca2+ at an extracellular pH greater than 7.4. In contrast, resuspension of capacitated spermatozoa into isotonic sucrose or choline-based media containing no added Na+ and K+ (pH 7.8) did not support acrosome reactions in response to the addition of Ca2+. Examination under the electron microscope showed that these spermatozoa responded to added Ca2+ with swelling or cavitation of the acrosomal matrix but fusion of the plasma membrane and acrosomal membrane did not occur. Treatment of spermatozoa with monensin, a monovalent cationic ionophore, induced rapid acrosome reactions in the presence of extracellular Ca2+ and Na+. In contrast, spermatozoa incubated for 3 h in a sucrose-based Na+-deficient medium or Medium MCM-PL containing 10 mM-KCl failed to give a significant percentage of acrosome reactions in response to the addition of Ca2+, but the addition of ouabain (0.1 mM) prevented the K+ inhibition. Amiloride, a sodium channel blocker in various other tissues, retarded the development of acrosome reactions of spermatozoa incubated in Medium MCM-PL. Based on these data, it appears that an increase in intracellular Na+ has a functional role in acquisition of guinea-pig sperm fertilizing ability.
D000177:Acrosome / Q000502:physiology*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000648:ultrastructure; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D008297:Male; D008854:Microscopy, Electron; D008985:Monensin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D013075:Sperm Capacitation / Q000187:drug effects; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure
D010042:Ouabain; D000584:Amiloride; D008985:Monensin; D012964:Sodium; D002118:Calcium