Thapsigargin elevates and potentiates the ability of progesterone to increase intracellular free calcium in human sperm: possible role of perinuclear calcium.
The effect of thapsigargin on intracellular free calcium ([Ca2+]i) was examined in swim up human sperm. Thapsigargin elevated [Ca2+]i in a dose dependent manner, with maximal effects observed with 10 microM. The increase in [Ca2+]i was relatively slow in taking 3-4 min to reach a maximal level. The increase in [Ca2+]i was inhibited when extracellular Ca2+ was chelated with EGTA, thus the source of Ca2+ for the increase was extracellular. The effect of thapsigargin to stimulate Ca2+ influx was also observed using the Mn2+ quenching of intracellular Fura-2. Thapsigargin pre-treatment of sperm was able to potentiate the effects of progesterone to elevate [Ca2+]i. Progesterone pre-treatment also potentiated the ability of thapsigargin to elevate [Ca2+]i. Further evidence to support the idea that thapsigargin was promoting Ca2+ influx was the fact that thapsigargin potentiated ionomycin (an agent that can increase Ca2+ cycling across phospholipid membranes) induced elevations in [Ca2+]i. Conversely, ionomycin also potentiated thapsigargin induced elevations in [Ca2+]i. It is concluded from these studies that high concentrations of thapsigargin are able to stimulate Ca2+ influx in human sperm by a mechanism not involving the endoplasmic reticulum Ca(2+)-ATPase pump since this organelle is absent in mature sperm. However, a likely site of action of thapsigargin in mature sperm is at the level of the nuclear membrane Ca(2+)-ATPase pump which is identical to the endoplasmic reticulum Ca(2+)-ATPase pump and is sensitive to inhibition by thapsigargin.
Department of Pharmacology, Eastern Virginia Medical School, Norfolk.
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PF
Blackmore
D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D004357:Drug Synergism; D004533:Egtazic Acid / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D008345:Manganese / Q000494:pharmacology; D009685:Nuclear Envelope / Q000378:metabolism; D011374:Progesterone / Q000494:pharmacology*; D013094:Spermatozoa / Q000187:drug effects* / Q000378:metabolism; D013268:Stimulation, Chemical; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D013729:Terpenes; D008345:Manganese; D011374:Progesterone; D004533:Egtazic Acid; D015759:Ionomycin; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium