Chloride Secretion in Kidney Distal Epithelial Cells (A6) Evoked by Cadmium

Abstract

The effect of Cd2+ on chloride secretion was examined in A6 renal epithelia cells by chloride-sensitive fluorescence (SPQ probe) and by the short-circuit-current (Isc) technique. Depleting the cells of Cl− suggests that the Cd2+-activated Isc (ΔIsc(Cd)) is dependent on the presence of Cl− ions. Among the Cl−-channel inhibitors the fenemates, flufenamic acid (FFA) and niflumic acid (NFA), and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) significantly lowered ΔIsc(Cd) compared with control level. In SPQ-loaded A6 cells, Cd2+ evoked an increase in Cl− secretion ([ΔCl−]Cd), which significantly exceeded the basal Cl− transport and was blockable by FFA and NFA. The closely related metals, Zn2+ or Ni2+, were also able to activate Cl− secretion. Preexposure of Zn2+ or Ni2+ completely prevented [ΔCl−]Cd, suggesting that Zn2+ and Ni2+ probably use similar mechanisms. Like Cd2+, thapsigargin (TG), an inhibitor of intracellular Ca2+-ATPase and the Ca2+-ionophore A23187, induced an increase in Isc. Moreover, TG and Cd2+ were able to neutralize the responses of the counterparts as also observed in Isc measurements, which indicates that Cd2+ activates Cl− secretion in a Ca2+-dependent manner. Hence, this study supports the idea that basolateral Cd2+ (possibly also Zn2+ and Ni2+), probably through a Ca2+-sensing receptor, causes calcium mobilization that activates apical fenemate-sensitive chloride channels leading to chloride secretion in A6 cells.