Zinc activates KCNQ1 and KCNN4 K+ channels in T84 secretory epithelial cells

Abstract

Basolateral membrane K+ channels establish the electrical driving force for anion secretion by epithelial tissues. We determined the effects of Zn2+, an inhibitor of anion secretion, on these channels in T84 human colonic epithelial cells. After Cl− secretion was stimulated in monolayers by chlorophenylthio‐cAMP (50 μM), serosal Zn2+ (2mM, zinc acetate) rapidly increased the short circuit current (Isc) from 32±5 to 93±8 μA/cm2, followed by inhibition to 17.1±3.2 (n=6). To determine the mechanisms of activation, tissues were pretreated with the KCNQ1 inhibitor 293B (100 μM) in the serosal solution, which reduced the Zn2+‐activated Isc by 57%. The KCNN4 inhibitor TRAM‐34 (10 μM) reduced activation by 76%. Thus, Zn2+ activated both KCNQ1 and KCNN4 K+ channels. Activation of K+ current by Zn2+was seen in isolated voltage‐clamped cells (233±103 pA, n=4). Fura‐2 fluorescence ratio measurements in isolated cells showed Zn2+ caused a slow rise in Ca2+ which was blocked by the intracellular Zn2+ chelator, pyridylmethylethylenediamine (TPEN), suggesting that Zn2+ can act on intracellular sites. Since Zn2+can modify disulfide bonds, we exposed T84 monolayers to the thiol reagent, dithiothreitol (DTT, 5mM), and like Zn2+, DTT transiently stimulated Isc (43±4 to 82±2 μA/cm2, n=3). These results suggest Zn2+activates basolateral membrane K+ channels, probably via effects on disulfide bonds. (Supported by NIH AI 181528)