NaCl flux in the flounder (Pseudopleuronectes americanus) intestine: effects of pH and transport inhibitors.

1. The effects of extracellular pH on Na+ and Cl- absorption were studied in vitro in the small intestine of the winter flounder, Pseudopleuronectes americanus. 2. Reductions in bathing solution pH inhibited JNams (mucosal-to-serosal flux) and JNanet (net flux) (r = 0.90) and JClnet (r = 0.92) [due to an increase in JClsm (serosal-to-mucosal)] and decreased short circuit current (Isc). 3. Luminal bumetanide (0.1 mM) and amiloride (1 mM) inhibited Na+ and Cl- absorption by reducing Jms. 4. Luminal barium (5 mM) and luminal copper (100 microM) decreased JClms and increased JClsm. 5. We conclude that reductions in extracellular pH inhibit a luminal membrane NaCl absorptive process (Na(+)-K(+)-2Cl-) and stimulate an electrogenic Cl- secretory process.