Multiple effects of econazole on calcium signaling: depletion of thapsigargin-sensitive calcium store, activation of extracellular calcium influx, and inhibition of capacitative calcium entry

The effect of econazole on intracellular calcium levels ([Ca2+](i)) in Madin Darby canine kidney cells was investigated using fura-2 fluorimetry. Econazole increased [Ca2+](i) dose-dependently at 5-50 mu M. The Ca2+ signal consisted of an initial rise, a gradual decay and a sustained plateau. Extracellular Ca2+ removal partially reduced the econazole response. Mn2+ quench of fura-2 fluorescence confirmed econazole-induced Ca2+ influx. The econazole-sensitive intracellular Ca2+ store overlaps with that sensitive to thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+ pump, because 25 mu M econazole depleted the thapsigargin-sensitive store, and conversely, thapsigargin abolished the econazole response. Econazole (25-50 mu M) partially inhibited capacitative Ca2+ entry induced by cyclopiazonic acid, another endoplasmic reticulum Ca2+ pump inhibitor, measured by depleting internal Ca2+ store in Ca2+-free medium followed by adding 10 mM CaCl2. Econazole induced capacitative Ca2+ entry itself. Pretreatment with La3+ (100 mu M) partially inhibited 25 mu M econazole-induced Mn2+ quench of fura-2 fluorescence, and La3+ immediately reduced 25 mu M econazole-induced Ca2+ signal when added at the peak of the signal, suggesting that econazole induced Ca2+ influx via two separate pathways: one is sensitive to La3+, the other is not. La3+ enlarged 25 mu M econazole-induced [Ca2+](i) transient during the decay phase. The econazole response was not altered when the cytosolic level of inositol 1,4,5-trisphosphate was inhibited by the phospholipase C inhibitor U73122. (C) 1999 Elsevier Science B.V. All rights reserved.