Dual action of palmitoyl trifluoromethyl ketone (PACOCF₃) on Ca²⁺ signaling: activation of extracellular Ca²⁺ influx and alteration of ATP- and bradykinin-induced Ca²⁺ responses in Madin Darby canine kidney cells

Abstract.

The effect of the phospholipase A₂ inhibitor palmitoyl trifluoromethyl ketone (PACOCF₃) on Ca²⁺ signaling in Madin Darby canine kidney (MDCK) cells was examined using fura-2 as the fluorescent Ca²⁺ indicator. At a concentration of 20 µM, PACOCF₃ did not change basal cytosolic free calcium concentrations ([Ca²⁺]_i), but at concentrations of 50–250 µM PACOCF₃ induced an increase in [Ca²⁺]_i by activating extracellular Ca²⁺ entry which was partly suppressed by 50 µM La³⁺. The effect of PACOCF₃ was abolished by removal of extracellular Ca²⁺. PACOCF₃ (10 µM) enhanced both the peak value and the area under the curve of the [Ca²⁺]_i increase induced by 10 µM ATP and 1 µM bradykinin by potentiating extracellular Ca²⁺ influx without affecting internal Ca²⁺ release. Several other phospholipase A₂ inhibitors had no effect on basal [Ca²⁺]_i or agonist-induced [Ca²⁺]_i increases. Collectively, the results suggest that PACOCF₃ alters Ca²⁺ signaling in renal tubular cells in a manner independent of phospholipase A₂ inhibition.