Relationship between plasma membrane Ca(2+)-ATPase activity and acrosome reaction in guinea pig sperm.
The results obtained by biochemical measurement demonstrated for the first time that significant decrease of the plasma membrane Ca(2+)-ATPase activity occurred during capacitation and acrosome reaction of guinea pig sperm. Ethacrynic acid, one kind of Ca(2+)-ATPase antagonists, inhibited the plasma membrane Ca(2+)-ATPase activity, but calmodulin (50 micrograms/mL) and trifluoperazine (200-500 mumol/L) did not, suggesting that calmodulin is not involved in ATP-driven Ca2+ efflux from sperm. However, calmodulin is involved in the control of Ca2+ influx. TFP, one kind of calmodulin antagonists, accelerated the acrosome reaction and Ca2+ uptake into sperm cells significantly. Ca(2+)-ATPase antagonists, quercetin, sodium orthovandate, furosemide and ethacrynic acid promoted the acrosome reaction, but inhibited Ca2+ uptake, which cannot be explained by their inhibitory effects on the plasma membrane Ca(2+)-ATPase activity. It is speculated that this phenomenon might be caused by simultaneous inhibitions of the activities of Ca(2+)-ATPase present in the plasma membrane, the outer acrosome membrane and the outer mitochondrion membrane resulting in Ca2+ accumulation in the cytoplasm, which in turn blocks further Ca2+ entry through some negative feedback mechanism(s). The inhibitory effect of Ca(2+)-ATPase antagonist on glycolytic activity may also be the reason for Ca2+ accumulation in cytoplasm and inhibition of Ca2+ uptake.
Li
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M
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.
Chen
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D
D000177:Acrosome / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D004976:Ethacrynic Acid / Q000494:pharmacology*; D006168:Guinea Pigs; D008297:Male; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000201:enzymology*
D002147:Calmodulin; D000252:Calcium-Transporting ATPases; D004976:Ethacrynic Acid; D002118:Calcium