Zn2+ increases resting cytosolic Ca2+ levels and abolishes capacitative Ca2+ entry induced by ATP in MDCK cells

The effect of Zn2+ on Ca2+ signaling in Madin Darby canine kidney (MDCK) cells was investigated by measuring the changes in the fluorescence of the Ca2+-sensitive dye fura-2. Zn2+ significantly increased cytoplasmic free Ca2+ levels ([Ca2+](i)) at concentrations of 2-100 mu M The maximum response was obtained at concentrations of 25-100 mu M. The [Ca2+](i) rise induced by 100 mu M Zn2+ consisted of a gradual rise and a plateau phase, and was primarily mediated by La3+-sensitive extracellular Ca2+ influx because the [Ca2+](i) rise was abolished by pretreatment with 100 mu M La3+ or removal of extracellular Ca2+, and that Zn2+ induced Mn2+ quench of fura-2 fluorescence at 360 nm excitation wavelength which was prevented by pretreatment with 100 mu M La3+ Pretreatment with 100 mu M Zn2+ for 220 s did not reduce the [Ca2+](i) rise induced by the endoplasmic reticulum (ER) Ca2+ pump inhibitor, thapsigargin, suggesting that Ca2+ release from the ER played a minor role in the Zn2+-induced [Ca2+](i) rise. Zn2+ (100 mu M) nearly abolished the capacitative Ca2+ entry induced by ATP (100 mu M). We also investigated the effect of Zn2+ pretreatment on the [Ca2+](i) rise induced by ATP. Zn2+ (100 mu M) affected ATP-induced [Ca2+](i) rise by abolishing capacitative Ca2+ entry and increasing [Ca2+](i) on its own without altering Ca2+ release from intracellular sources. The effect of Zn2+ on [Ca2+](i) was dissociated from changes in membrane potential.