Thapsigargin stimulates acrosomal exocytosis in hamster spermatozoa

Thapsigargin (TG), a plant-derived sesquiterpene lactone, inhibits several isoforms of both the sarcoplasmic and endoplasmic reticulum Ca 2+- ATPases. Thus, intracellular Ca 2+ stores found in the endoplasmic reticulum can be released by this compound. The mammalian sperm acrosome reaction (AR) depends on influx of extracellular Ca 2+. However, few reports have presented evidence for the involvement of putative Ca 2+ stores and intracellular Ca 2+ 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 Ca 2+ since ethyleneglycol-bis-(b-amino- ethyl ether) N,N'-tetra-acetic acid added 1 min before TG completely inhibited AR stimulation. The Ca 2+ c