Ca2+ mobilization induced by ?-hexachlorocyclohexane in Madin Darby canine kidney cells

The effect of the pesticide δ-hexachlorocyclohexane (δ-HCH) were examined on Ca 2+ signaling in Madin Darby canine kidney (MDCK) using fura-2 as a Ca 2+ probe. δ-HCH at concentrations of 5-200 mM increased intracellular free Ca 2+ concentration ([Ca 2+ ] i ) concentration-dependently. The [Ca 2+ ] i increase comprised an immediate rise followed by a sustained phase within 5 min of measurement. External Ca 2+ removal slightly reduced the [Ca 2+ ]i increase. In Ca 2+ -free medium, 150 μM δ-HCH did not increase [Ca 2+ ] i after pretreatment with carbonylcyanide m-chlorophenylhydrazone (CCCP; 2 μM), a mitochondrial uncoupler, and two endoplasmic reticulum (ER) Ca 2+ pump inhibitors, thapsigargin (1 μM) and cyclopiazonic acid (100 μM). Conversely, pretreatment with δ-HCH prevented thapsigargin, cyclopiazonic acid, and CCCP from releasing more Ca 2+ , suggesting 150 μM δ-HCH released Ca 2+ from the ER and mitochondria. δ-HCH (150 μM) activated Mn 2+ quench of fura-2 fluorescence, confirming that b-HCH induced Ca 2+ influx. Addition of 3 mM Ca 2+ induced a concentration-dependent [Ca 2+ ] i increase after pretreatment with 100-200 μM b-HCH for 870 sec in Ca 2+ -free medium. The δ-HCH (150 μM)-induced Ca 2+ release was decreased by inhibiting phospholipase C with 1 μM U73122. Collectively, we have found that δ-HCH increased [Ca 2+ ] i in MDCK cells by releasing Ca 2+ from the ER and mitochondria, followed by capacitative Ca 2+ entry.