Calcium uptake in human spermatozoa: characterization and mechanisms.
Basal 45Ca2+ influx was analyzed in human seminal spermatozoa using a method that allows these highly reactive cells to be easily and safely handled. The uptake was a time-dependent process, with its maximum at 400 s. The kinetics of 45Ca2+ transport was saturating as a function of extracellular Ca2+ concentration with a Km of 429 microM and a Vmax of 1.6 nmol 45Ca2+/mg protein/2.5 min. Depolarizing conditions and the calcium channel blocker verapamil did not affect the uptake; based on this, the presence of operating calcium channels in seminal spermatozoa is excluded. The independence of 45Ca2+ uptake on external concentration of both Na+ and Ca2+ suggests that Na+/Ca2+ exchange does not occur in these cells. The anticalmodulin drug trifluoperazine, the mitochondrial inhibitor antimycin A, and the SH reagents N-ethylmaleimide and mersalyl all inhibited the ion transport. A calmodulin-regulated, energy-requiring, proteinaceous Ca2+ transporter seems to be the main operating mechanism of calcium uptake in human seminal gametes.
Silvestroni
L
L
Institute of Clinica Medica V, University of Rome, La Sapienza, Italy.
Menditto
A
A
D000968:Antimycin A / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008297:Male; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013997:Time Factors; D014268:Trifluoperazine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D013439:Sulfhydryl Reagents; D014268:Trifluoperazine; D000968:Antimycin A; D014700:Verapamil; D002118:Calcium