Localization, Trafficking, and Significance for Acid Secretion of Parietal Cell Kir4.1 and KCNQ1 K+ Channels

Background & Aims: K+ recycling at the apical membrane of gastric parietal cells is a prerequisite for gastric acid secretion. Two K+ channels are currently being considered for this function, namely KCNQ1 and inwardly rectifying K+ channels (Kir). This study addresses the subcellular localization, trafficking, and potential functional significance of KCNQ1 and Kir4.1 channels during stimulated acid secretion. Methods: The effect of pharmacologic KCNQ1 blockade on acid secretion was studied in cultured rat and rabbit parietal cells and in isolated mouse gastric mucosa. The subcellular localization of KCNQ1 and Kir4.1 was determined in highly purified membrane fractions by Western blot analysis as well as in fixed and living cells by confocal microscopy. Results: In cultured parietal cells and in isolated gastric mucosa, a robust acid secretory response was seen after complete pharmacologic blockade of KCNQ1. Both biochemical and morphologic data demonstrate that Kir4.1 and KCNQ1 colocalize with the H+/K+-ATPase but do so in different tubulovesicular pools. All Kir4.1 translocates to the apical membrane after stimulation in contrast to only a fraction of KCNQ1, which mostly remains cytoplasmic. Conclusions: Acid secretion can be stimulated after complete pharmacologic blockade of KCNQ1 activity, suggesting that additional apical K+ channels regulate gastric acid secretion. The close association of Kir4.1 channels with H+/K+-ATPase in the resting and stimulated membrane suggests a possible role for Kir4.1 channels during the acid secretory cycle.