Importance of sodium ion to the progesterone-initiated acrosome reaction in human sperm.
Progesterone (P) has previously been shown to rapidly increase free intracellular calcium concentration ([Ca2+]i), and subsequently to initiate the acrosome reaction (AR) in capacitated human sperm. The present study used cytochemical analysis of the AR, and spectrofluorometric determination of sperm [Ca2+]i and intracellular pH (pHi) in Na(+)-containing and Na(+)-deficient bicarbonate/CO2-buffered media to investigate the role of Na+ in these P-initiated changes. We found that P failed to initiate the AR in Na(+)-deficient medium, and that the initial rise in [Ca2+]i following P (1 microgram/ml) stimulation was similar for both media; however, the [Ca2+]i in the Na(+)-deficient medium regressed more rapidly and plateaued at a significantly lower [Ca2+]i. Moreover, the differences in plateau [Ca2+]i were directly related to the percentage of acrosome reactions, suggesting that the plateau phase is not due to [Ca2+]i, but rather to the release of intracellular fura-2 into the medium during the AR. These [Ca2+]i, and AR results are in contrast to those reported previously by others for human sperm and suggest that a Na(+)-dependent mechanism is important in the P-initiated human sperm AR. Such a Na+ requirement may reflect the involvement of this ion in pHi regulation, as capacitated sperm that were incubated in a Na(+)-deficient medium for > or = 30 min displayed a significantly lower pHi.
Garcia
M A
MA
Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis 95616, USA.
Meizel
S
S
D000177:Acrosome / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002451:Cell Compartmentation; D004396:Coloring Agents / Q000378:metabolism; D016257:Fura-2 / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008297:Male; D011374:Progesterone / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology*; D013075:Sperm Capacitation
D004396:Coloring Agents; D007477:Ions; D011374:Progesterone; D012964:Sodium; D002118:Calcium; D016257:Fura-2