Calcium and phospholipase A2 are both required for the acrosome reaction mediated by G-proteins stimulation in human spermatozoa

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Abstract
G‐proteins, calcium, and phospholipase A2 (PLA2) have all been implicated in the cascade of signaling events leading to the acrosome reaction in human spermatozoa. In order to study the role of Ca+2 and PLA2 during the acrosome reaction triggered by G‐proteins, we treated human spermatozoa incubated for 3 hr under capacitating conditions with several reagents (GTPγS, A23187, ONO‐RS‐082, arachidonic acid, BAPTA‐AM, and TPEN), alone or in different combinations. Our results suggest that GTP‐binding proteins require Ca+2 and PLA2 to accomplish their stimulatory effect, and that Ca+2 is also required when the acrosome reaction—bypassing the action of PLA2—is stimulated by AA. Accordingly, when treated with GTPγS or AA, the cells loaded with Fura 2‐AM showed a steady increase of [Ca+2]i. On the other hand, a massive influx of Ca+2 was completely unable to induce the acrosome reaction if PLA2 was inhibited, suggesting that both an increase of [Ca+2]i and PLA2 activation are required for the acrosome reaction to occur. Mol. Reprod. Dev. 52:297–302, 1999.

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