In order to elucidate the biochemical mechanism of sperm capaeitation, the relationship between plasmalemma Na, K-ATPase, capacitation and acrosome reaction was investigated.Plasmalemma of guinea pig spermatozoa was isolated by sucrose gradient centrifugation for the determination of Na, K-ATPase activity. As far as the authors are aware, the Na, K-ATPase activity in plasmalemma of the guinea pig has never been detected. By treating sperm plasmalemma with 0.05% DOC (deoxycholate), enzyme activity could be quantitatively measured. After spermatozoa were incubated in capacitation medium for 8 h, Na, K-ATPase activity was found to be decreased to 35.6% as compared with that before incubation. The spermatozoa incubated for 10.5h in capacitationmedium containing 1 and 5μmol/L ouabain showed 46.5% and 64.4% acrosome reactions respectively, while the acrosome reaction of the control group was only 27.4%. The above results suggest that the decrease in the Na, K-ATPase activity of guinea pig spermatozoa may be
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