CALCIUM-TRANSPORT AND CA++-ATPASE ACTIVITY IN SPERMATOZOAL PLASMA-MEMBRANE VESICLES OF NIFEDIPINE-ADMINISTERED GUINEA-PIGS

Spermatozoal plasma membrane vesicles isolated from distal portion of the epididymis and vas deferens were found to contain Ca++-activated ATPase and calcium transport activities. Nifedipine was administered at two different doses (1.0 and 2.5 mg/kg b.w./day) and the effect was observed for both short- (4 week) and long-tern (12 week) period. The cellular ionic calcium content and Ca++-ATPase activity were observed to be enhanced in the drug-treated animals. The recovery studies carried out after 4 and 6 weeks of withdrawal of the drug treatment exhibited partial to complete restoration of observed changes. The stimulatory rather than inhibitory effect of Nifedipine, a specific calcium channel blocker, on calcium uptake may suggest that voltage-sensitive calcium channels may be lacking in guinea pig spermatozoa. The stimulatory effect of the drug is speculated to be either by inhibition of Na+-Ca++ antiporter or G-protein activated agonistic effect or probably due to altered physicochemical properties of the drug-treated sperm plasma membranes.