Roles for Potassium and Calcium Channels in the Initiation of Sperm Motility in Rainbow Trout.

It is well known that the motility of spermatozoa in rainbow trout is suppressed by K⁺. We showed here that although trout sperm are completely immotile in medium containing 5 mM K⁺, motility was initiated by the subsequent addition of several mM Ca²⁺, suggesting that both K⁺and Ca²⁺are related to the process of the initiation of sperm motility. It was further found that K⁺channel blockers tetraethylammonium, nonyltriethylammonium, Ba²⁺and Cs⁺, as well as the Ca²⁺channel blocker verapamil, inhibited the initiation of sperm motility at doses at which these reagents inhibit chnnel-related functions in other cells. However, Na⁺channel blocker, tetrodotoxin and anion channel blocker 4, 4-diisothiocyatatostilbene-2, 2'-disulfonic acid inhibited the motility only at extremely high doses. These results suggest that transport of K⁺and Ca²⁺through ion channels at the plasma membrane of spermatozoa is the first event that triggers the initiation of sperm motility in rainbow trout.