Acrosome reaction stimulated by the GTP non-hydrolizable analogue GTPγS is blocked by phospholipase A2inhibitors in human spermatozoa

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Abstract
Phospholipase A2 (PLA2, EC 3.1.1.4) is involved in the cascade of signalling events leading to the acrosome reaction in human spermatozoa. In order to study the role of PLA2 in the acrosome reaction triggered by GTP gamma S, a non-hydrolizable analogue of GTP, two well-known PLA2 inhibitory reagents were used: dexamethasone (1 mM, a synthetic glucocorticoid), and 2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid (ONO-RS-082, 320 micrograms/ml). Normal human spermatozoa were incubated for 3 h under capacitating conditions and treated with several reagents [GTP gamma S, dexamethasone, ONO-RS-082, arachidonic acid (AA) and lysophosphatidylcholine (LPC)], alone or in different combinations. In confirmation of earlier reports, GTP gamma S induced the acrosome reaction. On the other hand, dexamethasone and ONO-RS-082 were both able to inhibit the acrosome reaction induced by GTP gamma S. However, when AA or LPC was added after dexamethasone or ONO-RS-082, the acrosome reaction reached values close to those obtained using GTP gamma S alone. It is concluded that PLA2 probably plays an active role in the acrosome reaction triggered by GTP-binding proteins.