Thapsigargin stimulates acrosomal exocytosis in hamster spermatozoa.
Thapsigargin (TG), a plant-derived sesquiterpene lactone, inhibits several isoforms of both the sarcoplasmic and endoplasmic reticulum Ca2+-ATPases. Thus, intracellular Ca2+ stores found in the endoplasmic reticulum can be released by this compound. The mammalian sperm acrosome reaction (AR) depends on influx of extracellular Ca2+. However, few reports have presented evidence for the involvement of putative Ca2+ stores and intracellular Ca2+ mobilization in the AR. Thus, we designed experiments to evaluate the effect of TG on the hamster sperm AR. Thapsigargin stimulated-in a dose-dependent manner-the AR of spermatozoa previously capacitated for at least 3 hr, not affecting sperm motility. A maximal stimulatory effect was apparent 3 min after addition of TG to spermatozoa previously capacitated for 4 hr and was dependent on external Ca2+ since ethyleneglycol-bis-(b-amino-ethyl ether) N,N'-tetra-acetic acid added 1 min before TG completely inhibited AR stimulation. The Ca2+ channel blockers diltiazem and nifedipine also abolished the TG-stimulatory effect when added to capacitated spermatozoa 10 min before the inhibitor. In addition, the trypsin inhibitors p-nitrophenyl-p'-guanidine-benzoate hydrochloride and benzamidine added to the sperm suspensions 10 min before TG inhibited by 70-80% the TG-induced AR. These results indicate that putative Ca2+ stores release may be involved in stimulation of extracellular Ca2+ influx required for the occurrence of the AR. In addition, a sperm trypsin-like protease may be part of the mechanism by which TG induces the hamster sperm AR.
Unidad de Biología de la Reproducciíon, INTA, Universidad de Chile, Santiago. mllanos@uec.inta.uchile.cl
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D000177:Acrosome / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005089:Exocytosis / Q000187:drug effects*; D008297:Male; D008647:Mesocricetus; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D019284:Thapsigargin