High pH-induced acrosome reaction and Ca2+ uptake in sea urchin sperm suspended in Na+-free seawater.
The egg jelly-induced acrosome reaction of sea urchin sperm requires the presence of Ca2+ and Na+ in seawater at its normal pH 8. Sperm suspended in seawater at pH 9 undergo the acrosome reaction in the absence of jelly. We have attempted to understand the role of external Na+ in this reaction. Sperm were suspended in Na+-free seawater and the percentage of acrosome reaction and the amount of Ca2+ uptake were determined as a function of external pH. High pH (9.0) in Na+-free medium without jelly triggered a high percentage (above 65%) of sperm acrosome reactions and a two to fourfold increase in Ca2+ uptake. Both the percentage of acrosome reactions and the amount of Ca2+ uptake were similar to those induced by either jelly or pH 9 in Na+-containing seawater. On the other hand, the absence of Na+ in seawater inhibits jelly from inducing Ca2+ uptake and acrosome reactions at pH 8.0 and even at pH 8.5. These results indicate that the Na+ requirement for the acrosome reaction induced by jelly is lost when triggering is by high pH. In contrast, Ca2+ was strictly required since sperm did not react in Ca2+-free seawater at pH 9. We also found that like the jelly-induced acrosome reaction the high-pH-induced acrosome reaction and Ca2+ uptake in complete and Na+-free seawater were inhibited by D600. This finding suggests that the same transport system for Ca2+ uptake associated with the acrosome reaction operates at both triggering conditions, i.e., jelly or pH 9. Although D600 is not now considered a specific blocker, its effect has suggested the involvement of Ca2+ channels in the acrosome reaction. This proposal is supported by our results with nisoldipine, a highly specific inhibitor of calcium channels. The drug inhibited both the sperm acrosome reaction and Ca2+ uptake induced by jelly or pH 9 in complete seawater.
D000177:Acrosome / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005260:Female; D005711:Gallopamil / Q000494:pharmacology; D005782:Gels / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008297:Male; D010063:Ovum / Q000502:physiology; D012617:Sea Urchins / Q000502:physiology*; D012623:Seawater; D012964:Sodium / Q000494:pharmacology* / Q000502:physiology; D013094:Spermatozoa / Q000378:metabolism* / Q000502:physiology*; D013997:Time Factors
D002121:Calcium Channel Blockers; D005782:Gels; D005711:Gallopamil; D012964:Sodium; D002118:Calcium