Functional expression of sperm angiotensin II type I receptor in Xenopus oocyte: modulation of a sperm Ca2+-activated K+ channel

In addition to Ca2+ and K+ fluxes, angiotensin II (Ang II) has been shown t o influence sperm motility. The present study investigated the involvement of angiotensin II type 1 receptor (ATI) in mediating the modulatory effect of Ang II on a sperm Ca2+-activated K+ channel expressed in Xenopus oocytes injected with RNAs of spermatogenic cells. Ang II at a concentration of 1 mu M was found to potentiate the ionomycin-induced current, previously demo nstrated to be mediated by a 'Maxi' Ca2+-activated K+ channel. However, at higher concentration, 20 mu M, Ang II was found to suppress the ionomycin-i nduced current. Both potentiating and inhibitory effects of Ang II were blo cked by losartan, a specific antagonist of AT(1) receptors. Immunohistochem ical studies further confirmed the presence of AT(1) receptors in spermatog enic cells while expression of AT(1) receptor mRNA was demonstrated by RT-P CR. These results suggest that Ang II may influence sperm motility as well as other sperm function by acting on AT(1) receptors, and exerting potentia ting and inhibitory effects on the Ca2+-activated K+ channels. (C) 1998 Els evier Science B.V. All rights reserved.