Acid Secretion Associated Translocation of KCNJ15 in Gastric Parietal Cells

Potassium ions are required for gastric acid secretion. Several K+ channels have been implicated in providing K+ at the apical membrane of parietal cells. In examining the mRNA expression levels between gastric mucosa and the liver tissues, KCNJ15 stood out as the most highly specific K+ channel in the gastric mucosa. Western blot analysis confirmed that KCNJ15 is abundant in the stomach. Immunofluorescence staining of gastric glands indicated that KCNJ15 was expressed in the parietal cells and the chief cells, but not in the mucous neck cells. In resting parietal cells, KCNJ15 was mainly found in puncta throughout the cytoplasm, but distinct from H+,K+-ATPase. Upon stimulation, KCNJ15 and H+,K+-ATPase become co-localized on the apical membranes, as suggested by immunofluorescence staining. Western blot analysis of the resting and the stimulated membrane fractionations confirmed this observation. From non-secreting preparations, the KCNJ15 containing membranes and the H+,K+-ATPase containing tubulovesicles sedimented differently indicating that KCNJ15 is stored in vesicles distinct from the H+,K+-ATPase enriched tubulovesicles. Upon stimulation, KCNJ15 and H+,K+-ATPase both translocate to the apical membrane for active acid secretion. Thus KCNJ15 can be added to the family of apical K+ channels in gastric parietal cells. The specific roles for these different K+ channels remain to be determined.