Extracellular zinc stimulates a calcium-activated chloride conductance through mobilisation of intracellular calcium in renal inner medullary collecting duct cells

We have used the perforated patch clamp and fura-2 fluorescence techniques to study the effect of extracellular Zn²⁺ on whole-cell Ca²⁺-activated Cl⁻ currents (I _CLCA) in mouse inner medullary collecting duct cells (mIMCD-3). I _CLCA was spontaneously active in 74% of cells under basal conditions and displayed time and voltage-independent kinetics and an outwardly rectifying current/voltage relationship (I/V). Addition of zinc chloride (10–400 μM) to the bathing solution resulted in a dose-dependent increase in I _CLCA with little change in Cl⁻ selectivity or biophysical characteristics, whereas gadolinium chloride (30 μM) and lanthanum chloride (100 μM) had no significant effect on the whole-cell current. Using fura-2-loaded mIMCD-3 cells, extracellular Zn²⁺ (400 μM) stimulated an increase in intracellular Ca²⁺ to an elevated plateau. The Zn²⁺-stimulated [Ca²⁺]_i increase was inhibited by thapsigargin (200 nM), the IP₃ receptor antagonist 2-aminoethoxydiphenyl borate (10 μM) and removal of bath Ca²⁺. Pre-exposure to Zn²⁺ (400 μM) markedly attenuated the ATP (100 μM)-stimulated [Ca²⁺]_i increase. These data are consistent with the hypothesis that extracellular Zn²⁺ stimulates an increase in [Ca²⁺]_i by a release of calcium from thapsigargin/IP₃ sensitive stores. A possible physiological role for a divalent metal ion receptor, distinct from the extracellular Ca²⁺-sensing receptor, in IMCD cells is discussed.