Abstract
The Cl-channel of the apical membrane of the gastric parietal cell was characterized in native rabbit H/K ATPase-containing membrane vesicles in bilayer reconstitution studies. It is a linear Cl- channel which exhibits activation by reduction of extracellular pH and PKA. The ClC-2 Cl- channel cloned from rabbit gastric mucosa and expressed in Xenopus laevis oocytes, exhibited similar electrophysiological characteristics and regulation as the native gastric Cl- channel. Potential PKA phosphorylation sites in rabbit ClC-2 appear to underlie PKA activation. The pH sensor on the extracellular surface of ClC-2 was identified as E419 and amidation resulted in activation of the channel. Recombinant ClC-2 stably expressed in HEK-293 cells showed Cl- currents that were activated by forskolin and IBMX, low extracellular pH, amidation, arachidonic acid and acid-activated omeprazole. Using immunofluorescent confocal microscopy, ClC-2 was localized to the secretory canalicular membrane of stimulated parietal cells and to intracellular structures (tubulovesicles) in resting parietal cells, which was confirmed by immunogold electron microscopy. Distribution of the gastric H/K ATPase and ClC-2 were similar. These findings strongly support the view that ClC-2 is the Cl- channel in the apical secretory membrane of the gastric parietal cell which, together and in concert with the H/K ATPase and a K+ channel, result in HCl secretion.
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