Involvement of Ca^2＋-activated K^＋Channels in Receptor-Regulated Sperm Motility in Rats

Ion fluxes have been implicated in sperm functions.A pivotal role of Ca2 hasbeen observed in variousreproductive events including sperm capacitation,acrosomereaction[1～ 3] ,sperm activation[4～ 5] and sperm motility[6～ 8] .The importance of Ca2 in-f…

Involvement of Ca2+-activated K+ Channels in Receptor-Regulated Sperm Motility in Rats

Previous voltage-clamp studies have demonstrated the modulation of sperm Ca2+-activated K+ (KCa) channels expressed in Xenopus oocytes by angiotensin Ⅱ (Ang Ⅱ)and extracellular ATP via AT1 receptor and P2U receptor, respectively. In the presentstudy, we investigated the involvement of KCa channels in receptor-regulated spermmotility of the rat using a computer-aided sperm analysis system, HTM-IVOS, in con-junction with Ca2+-mobilizing agents, receptor agonists/antagonists and KCa channelsblockers.The percentage of motile sperm was increased by ionomycin (0. 5 μmol/L), whichcould be inhibited by K+ channel blockers, tetraethylammonium (TEA 1 μmol/L ) orcharybdotoxin (ChTX, 300 nmol/L) indicating the presence of KCa channels. AngⅡ, at low concentration, 10 nmol/L, was found to increase motility, however, athigher concentration, 1 μmol/L, percentage of motility was found to be suppressed.Both stimulatory and inhibitory effects of Ang Ⅱ could be reversed by losartan, aspecific antagonist of AT 1 receptors, but not AT 2 antagonist PD123177, indicating theinvolvement of AT1 but not AT2 receptor in mediating both effects. ChTX also abol-ished both stimulatory and inhibitory effects of Ang H, suggesting the involvement ofKCa channels. The percentage of motility was also enhanced by extracellular ATP, afactor known to be involved in sperm activation. The ATP-enhanced sperm motilitywas mimicked by UTP , and inhibited by ChTX and reactive blue, an antagonist of P2receptor, indicating the involvement of both P2U and KCa channels. RT-PCR studywas also conducted to confirm the expression of KCa channels, AT1 receptors and P2Ureceptor, but not AT2 receptor, in rat caudal epididymal sperm. The present findingssuggest an important role of KCa channels in the regulation of sperm motility by AT1and P 2U receptors.