Calcium and phospholipase A(2) are both required for the acrosome reactionmediated by G-proteins stimulation in human spermatozoa

G-proteins, calcium, and phospholipase A(2) (PLA(2)) have all been implicat ed in the cascade of signaling events leading to the acrosome reaction in h uman spermatozoa. In order to study the role of Ca+2 and PLA(2) during the acrosome reaction triggered by G-proteins, we treated human spermatozoa inc ubated for 3 hr under capacitating conditions with several reagents (GTP ga mma S, A23187, ONO-RS-082, arachidonic acid, BAPTA-AM, and TPEN), alone or in different combinations. Our results suggest that GTP-binding proteins re quire Ca+2 and PLA(2) to accomplish their stimulatory effect, and that Ca+2 is also required when the acrosome reaction-bypassing the action of PLA(2) -is stimulated by AA. Accordingly, when treated with GTP gamma S 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 ac rosome reaction if PLA(2) was inhibited, suggesting that both an increase o f [Ca+2](i) and PLA(2) activation are required for the acrosome reaction to occur. Mol. Reprod. Dev. 52:297-302, 1999. (C) 1999 Wiley-Liss, Inc.