Novel effects of gossypol, a chemical contraceptive in man: mobilization of internal Ca2+ and activation of external Ca2+ entry in intact cells

AbstractThe effect of gossypol on Ca2+ signaling in Madin Darby canine kidney (MDCK) cells was investigated by using fura-2 as a Ca2+ probe. Gossypol evoked a rise in cytosolic free Ca2+ levels ([Ca2+]i) concentration-dependently between 2 and 20 μM. The response was decreased by external Ca2+ removal. In Ca2+-free medium pretreatment with gossypol nearly abolished the [Ca2+]i increase induced by carbonylcyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, and thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+ pump; but pretreatment with CCCP and thapsigargin only partly inhibited gossypol-induced Ca2+ release. Addition of 3 mM Ca2+ induced a [Ca2+]i increase after pretreatment with 5 μM gossypol in Ca2+-free medium. This Ca2+ entry was decreased by 25 μM econazole, 50 μM SKF96365 and 40 μM aristolochic acid (a phospholipase A2 inhibitor). Pretreatment with aristolochic acid inhibited 5 μM gossypol-induced internal Ca2+ release by 55%, but suppression of phospholipase C with 2 μM 1-(6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione) had no effect. Gossypol (5 μM) also increased [Ca2+]i in human bladder cancer cells and neutrophils. Collectively, we have found that gossypol increased [Ca2+]i in MDCK cells by releasing Ca2+ from multiple Ca2+ stores in a manner independent of the production of inositol-1,4,5-trisphosphate, followed by Ca2+ influx from external space