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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Gastric parietal cell secretory membrane contains PKA- and acid-activated Kir2.1 K⁺ channels

Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0576

Submitted 11 September 2003 ; accepted in final form 22 October 2003

Our objective was to identify and localize a K⁺ channel involved in gastric HCl secretion at the parietal cell secretory membrane and to characterize and compare the functional properties of native and recombinant gastric K⁺ channels. RT-PCR showed that mRNA for Kir2.1 was abundant in rabbit gastric mucosa with lesser amounts of Kir4.1 and Kir7.1, relative to -actin. Kir2.1 mRNA was localized to parietal cells of rabbit gastric glands by in situ RT-PCR. Resting and stimulated gastric vesicles contained Kir2.1 by Western blot analysis at 50 kDa as observed with in vitro translation. Immunoconfocal microscopy showed that Kir2.1 was present in parietal cells, where it colocalized with H⁺-K⁺-ATPase and ClC-2 Cl^- channels. Function of native K⁺ channels in rabbit resting and stimulated gastric mucosal vesicles was studied by reconstitution into planar lipid bilayers. Native gastric K⁺ channels exhibited a linear current-voltage relationship and a single-channel slope conductance of 11 pS in 400 mM K₂SO₄. Channel open probability (P_o) in stimulated vesicles was high, and that of resting vesicles was low. Reduction of extracellular pH plus PKA treatment increased resting channel P_o to 0.5 as measured in stimulated vesicles. Full-length rabbit Kir2.1 was cloned. When stably expressed in Chinese hamster ovary (CHO) cells, it was activated by reduced extracellular pH and forskolin/IBMX with no effects observed in nontransfected CHO cells. Cation selectivity was K⁺ = Rb⁺ >> Na⁺ = Cs⁺ = Li⁺ = NMDG⁺. These findings strongly suggest that the Kir2.1 K⁺ channel may be involved in regulated gastric acid secretion at the parietal cell secretory membrane.

H⁺-K⁺-ATPase; hydrogen chloride secretion; parietal cell K⁺ channel

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