Effect of calmodulin antagonists on CA2+ uptake by boar spermatozoa

Calcium uptake by washed boar sperm suspensions is markedly stimulated by the calmodulin antagonists trifluoperazine and calmidazolium. Both 45Ca2+ uptake and net Ca2+ uptake are increased by these drugs. Drug stimulated Ca2+ uptake is blocked by verapamil (1 mM), by ruthenium red (25 microM) and by carbonyl cyanide p-trifluoromethoxyphenyl hydrazone. Calmodulin antagonists do not slow ATP-dependent Ca2+ extrusion from plasma membrane vesicles, and they do not inhibit plasma membrane Ca2+-ATPase. It is proposed that calmodulin is involved in the control of Ca2+ entry in boar spermatozoa. Most entering Ca2+ in uncapacitated spermatozoa is sequestered by mitochondria or rapidly extruded by plasma membrane pumps. In contrast to the uptake mechanism, ATP-dependent Ca2+ extrusion does not appear to be regulated by calmodulin.