ROLE OF BASOLATERAL NA-K+-CL- COTRANSPORT IN HCL SECRETION BY AMPHIBIAN GASTRIC-MUCOSA()

In amphibians and mammals, luminal H+ secretion by the stomach require s Cl-. It is widely accepted that a basolateral Cl-/HCO, exchanger in the acid-secreting oxyntic cell restores the Cl- deficit resulting fro m apical HCl secretion. In this study, we used reverse transcriptase-p olymerase chain reaction (RT-PCR) to generate a 1,200-bp fragment spec ific to a basolateral isoform of the Na+-K+-Cl- cotransporter in the g astric fundus of Necturus maculosus. By Northern analysis, we observed that gastric mucosa expresses greater than fivefold higher levels of mRNA encoding this cotransporter than any other tissue in the gastroin testinal tract. Feeding results in > 100% increases in mRNA levels in acid-secreting fundic mucosa but does not alter mRNA levels in the nei ghboring and non-acid-secreting antral mucosa or duodenum. Flux measur ements using in vitro fundic mucosae indicate that acid secretion requ ires Na+ in the nutrient (i.e., serosal side) perfusate, is modulated by changes in nutrient K+ levels, and is inhibited by nutrient solutio ns containing 50 mu M bumetanide, a recognized blocker of Na+-K+-Cl- c otransport. These findings suggest that this basolateral transporter p lays a dominant and previously unsuspected role in secretion of HCl ac ross the apical membrane.