title: Potassium ion influx and Na+,K+-ATPase activity are required for the hamster sperm acrosome reaction.
abstract: The role of a K+ ion influx and Na+,K+-ATPase activity in the hamster sperm acrosome reaction (AR) was examined, using a range of concentrations of K+,K+ ionophores and a Na+,K+-ATPase inhibitor. Washed epididymal hamster sperm, capacitated in vitro in an artificial medium containing 2 mM Ca2+, 147 mM Na+, and 3, 6, 12, 18, or 24 mM K+, began undergoing the AR after 3 h of incubation. Sperm incubated in low K+ (0.9 mM) failed to undergo the AR even after 5 h of incubation. Sperm in 0.9 mM K+ could be induced to undergo the AR when either K+ (12 mM) alone or K+ (12 mM) with 0.1 microM nigericin was added after 3.5 h of incubation. The addition of K+ alone stimulated the AR in 30 min, whereas nigericin plus K+ stimulated the AR 15 min after addition. Neither nigericin added alone (0.9 mM K+) nor nigericin plus 12 mM K+ added to a low Ca2+ (0.35 mM) system resulted in acrosome reactions. Valinomycin (1 nM) did not stimulate the AR when added together with K+ (3-24 mM) to sperm incubated in 0.9 mM K+ for 3.5 h but markedly decreased sperm motility. Micromolar levels of ouabain blocked the AR when added between t = 0--3 h to sperm incubated with 3-24 mM K+. Inhibition of AR by the addition of 1 microM ouabain to sperm incubated with 3 mM K+ was completely reversed by the addition of 0.1 microM nigericin at t = 3.5 h. These results suggest that Na+,K+-ATPase activity and the resulting K+ influx are important for the mammalian sperm AR. Some similarities between requirements for the hamster sperm AR and secretory granule exocytosis are discussed.
mesh_terms: D000177:Acrosome / Q000502:physiology*; D000818:Animals; D006224:Cricetinae; D005089:Exocytosis; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008647:Mesocricetus; D009550:Nigericin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000201:enzymology* / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D007476:Ionophores; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D009550:Nigericin; D011188:Potassium