Chloride efflux during the progesterone-initiated human sperm acrosome reaction is inhibited by lavendustin A, a tyrosine kinase inhibitor.

Previous studies showed that progesterone (P) can initiate the mammalian sperm acrosome reaction (AR) in vitro and that a sperm GABAA-like receptor/Cl- channel is involved in an essential Cl- efflux mediated by P during the AR. Here, we show that lavendustin A, a potent, specific inhibitor of tyrosine kinase activity, strongly inhibits the P-initiated human AR and the essential P-mediated Cl- efflux. Lavendustin B, a weak tyrosine kinase inhibitor, had no significant effect. These results suggest that, as part of AR initiation, P mediates tyrosine phosphorylation of the sperm GABAA- like receptor/Cl- channel.