The role of calcium and Ca2+-ATPase in maintaining motility in ram spermatozoa.

Extracellular calcium at millimolar concentrations inhibits collective motility of ejaculated ram spermatozoa. In untreated cells, or when motility was made dependent upon glycolytic activity, there is very small inhibition, but when motility was made dependent upon mitochondrial respiration there is very high inhibition in motility by increasing extracellular Ca2+ concentration. Quercetin, which inhibits (Ca2+ + Mg2+)-ATPase activity in isolated plasma membranes, also inhibits motility mainly in cells that have been made dependent upon glycolytic activity, but there is also inhibition in untreated cells. When motility was made dependent upon mitochondrial activity, there is no inhibition but rather some stimulation in motility by quercetin. The inhibitory effect of quercetin is enhanced by increasing Ca2+ concentration in the medium. Quercetin also inhibits uptake of calcium into the cells, in a mechanism by which a calcium channel is involved. This inhibition is high only when the glycolysis is inhibited in the cells. The rate of glycolysis is decreased by quercetin or ouabain, but their effects on motility are quite different. Based on these data, it appears that the plasma membrane (Ca2+ + Mg2+)-ATPase or the Ca2+ pump have a functional role in the regulation of spermatozoa motility. This motility regulation is functioning through mechanisms which include glycolytic activity and maintenance of intracellular calcium concentrations.