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Induction of a Sodium Ion Influx by Progesterone in Human Spermatozoa¹

^a Service d'Histologie-Embryologie-Biologie de la Reproduction, Université Paris V-Cochin, 75014 Paris, France ^b Université Paris XI, UFR Kremlin Bicètre, 92470 Kremlin Bicètre, France

In human spermatozoa, progesterone (P₄) induces a depolarization of the plasma membrane, a rapid calcium (Ca²⁺) influx, and a chloride efflux. The sodium ion (Na⁺) was partly responsible for the P₄-induced depolarizing effect but was not required for calcium influx. We used fluorescent probes for spectrofluorometry to investigate whether P₄ induced a Na⁺ influx and whether voltage-operated channels were involved in Na⁺ and/or Ca²⁺ entries. We found that 10 µM P₄ significantly increased intracellular Na⁺ concentration from 17.8 ± 2.0 mM to 27.2 ± 1.6 mM (P < 0.001). Prior incubation of spermatozoa with 10 µM flunarizine, a Na⁺ and Ca²⁺ voltage-dependent channel blocker, inhibited the sodium influx induced by 10 µM P₄ by 84.6 ± 15.4%. The Ca²⁺ influx induced by 10 µM P₄ was also significantly inhibited in a Na⁺-containing medium by 10 µM flunarizine or 10 µM pimozide (P < 0.01). In contrast, flunarizine had no inhibitory effect on the Ca²⁺ influx induced by 10 µM P₄ in spermatozoa incubated in Na⁺-depleted medium. The P₄-promoted acrosome reaction (AR) was significantly higher when spermatozoa were incubated in Na⁺-containing medium as compared to Na⁺-depleted medium. These data demonstrate that P₄ stimulates a Na⁺ influx that could be involved in the AR completion. They also suggest that voltage-dependent Na⁺ and Ca²⁺ channels are implicated in P₄-mediated signaling pathway in human spermatozoa.

First decision: 23 September 1999.

¹ This work was supported by grant no. 1752 from the Direction de la Recherche et des Etudes Doctorales.

² Correspondence: Catherine Patrat, Service d'Histologie-Embryologie-Biologie de la Reproduction, Université Paris V-Cochin, 24, rue du Faubourg Saint-Jacques, 75014 Paris, France. FAX: 33 01 58 41 15 75;catherine.patrat{at}cch.ap-hop-paris.fr

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