Potassium transport by flounder intestinal mucosa
Frizzell, R.A.; Halm, D.R.; Musch, M.W.; Stewart, C.P.; Field, M.
American Journal of Physiology 246(6 Pt 2): F946-F951
1984
ISSN/ISBN: 0002-9513 PMID: 6742138 Document Number: 241308
Small intestinal mucosa of the winter flounder (Pseudopleuronectes americanus) was used. The mechanisms of potassium transport across an epithelium in which NaCl absorption is mediated primarily by Na/K/Cl cotransport at the apical membrane were studied. Rubidium served as a reliable K substitute; under control conditions, both K and Rb were actively secreted. During secretion, K (Rb) enters across the basolateral membrane via the Na/K pump and exits across the apical membrane through K conductance pathways, since serosal ouabain or mucosal barium abolished K secretion, mucosal furosemide or Cl-free media blocked K secretion by interfering with access of Na to the pump, and increased mucosal solution K or Rb concentration depolarized the apical membrane electrical potential difference. Mucosal Ba unmasked active Rb absorption that could be blocked by mucosal furosemide. The findings illustrate active K absorption and secretion across an epithelium that comprises a single cell type in which opposing K fluxes across the apical membrane are mediated by Na/K/Cl cotransport entry and conductive K exit. Direction of transepithelial K transport is determined by relative activities of these pathways.