title: Effect of calmodulin antagonists on CA2+ uptake by boar spermatozoa.
abstract: 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.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000201:enzymology; D007093:Imidazoles / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D013094:Spermatozoa / Q000378:metabolism*; D013552:Swine; D014268:Trifluoperazine / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D007093:Imidazoles; D014268:Trifluoperazine; C031938:calmidazolium; D014700:Verapamil; D000252:Calcium-Transporting ATPases; D002118:Calcium