Progesterone-mediated calcium influx and acrosome reaction of human spermatozoa: pharmacological investigation of T-type calcium channels.
The mechanisms of the progesterone (P4)-activated Ca2+ influx and the relationship between the intracellular free Ca2+ concentration ([Ca2+]i) and the acrosome reaction (AR) were investigated in this study. We compared the [Ca2+]i of uncapacitated and capacitated human sperm populations in response to P4 stimulation; characterized the effects of the pharmacological agents pimozide and mibefradil, inhibitors of T-type voltage-operated calcium channels (VOCCT), on the P4-activated Ca2+ influx; and determined the effects of these drugs on the P4-initiated AR. Since pimozide can also inhibit calmodulin-dependent enzymes, we examined the effects of the calmodulin antagonist, calmidazolium, on the above-mentioned events. The basal [Ca2+]i and the amplitude of the P4-activated Ca2+ influx were significantly (p < 0.05) higher in capacitated sperm populations. Also, in capacitated sperm populations, all three pharmacological agents significantly (p < 0.05) inhibited the P4-activated Ca2+ influx (IC50): calmidazolium (0.7 microM) > pimozide (8 microM) > mibefradil (11 microM). By contrast, the effects of these drugs on the P4-initiated AR were varied: pimozide (10 and 20 microM) significantly (p < 0.05) increased the percentage of AR spermatozoa, calmidazolium was without effect, and mibefradil (20 microM) significantly (p < 0.05) inhibited the AR. These disparate results do not allow us to reach any definitive conclusion concerning the role of a sperm VOCCT in the mechanism of the P4-initiated AR. However, the differences between the [Ca2+]i and AR effects, in particular the inverse relationship in the case of pimozide, suggest a dissociation between the amplitude of the P4-stimulated Ca2+ signal and the downstream biological effect of that signal, the AR.
Garcia
M A
MA
Department of Cell Biology and Human Anatomy, University of California, Davis, California 95616, USA.
Meizel
S
S
D020101:Acrosome Reaction / Q000187:drug effects*; D001562:Benzimidazoles / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D018492:Dopamine Antagonists / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D020748:Mibefradil; D010868:Pimozide / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology*; D013075:Sperm Capacitation; D013081:Sperm Motility / Q000502:physiology; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*; D013764:Tetrahydronaphthalenes / Q000494:pharmacology
D001562:Benzimidazoles; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002147:Calmodulin; D018492:Dopamine Antagonists; D005456:Fluorescent Dyes; D007093:Imidazoles; D013764:Tetrahydronaphthalenes; D010868:Pimozide; D020748:Mibefradil; D011374:Progesterone; C031938:calmidazolium; D002118:Calcium; D016257:Fura-2