The neoglycoprotein mannose-bovine serum albumin, but not progesterone, activates T-type calcium channels in human spermatozoa

The neoglycoproteins alpha-D-mannose-bovine serum albumin (mannose-BSA) and N-acetyl-alpha-D-glucosamine-BSA (glucNAc-BSA) were shown to rapidly increase intracellular free calcium ([Ca(2+)](i)) in human spermatozoa. The increase in [Ca(2+)](i) induced by these neoglycoproteins accounts for the known ability of these compounds to induce the acrosome reaction in human spermatozoa. Our data support the hypothesis that mannose-BSA, but not progesterone, activates T-type Ca(2+) channels in human spermatozoa for the following reasons: (i) the capacity of mannose-BSA to increase [Ca(2+)](i) was inhibited by the specific T-type Ca(2+) channel blocker mibefradil (IC(50) = 10(-6) mol/l) while progesterone was not inhibited by 10(-5) M mibefradil; (ii) the effect of mannose-BSA to elevate [Ca(2+)](i) was inhibited more potently by Ni(2+) (IC(50) = 0.1 mmol/l) than Cd(2+) (IC(50) 0.5 mmol/l), whereas the effect of progesterone to elevate [Ca(2+)](i) was inhibited equally by Ni(2+) and Cd(2+) (IC(50) = 0.25 mmol/l); (iii) the effects of mannose-BSA and progesterone to increase [Ca(2+)](i) were greater than additive. These data support the idea that mannose-BSA and progesterone were activating distinct Ca(2+) channels, one of which was a T-type Ca(2+) channel activated by mannose-BSA whereas the Ca(2+) channel that was activated by progesterone has yet to be defined at the molecular level.