Ion transport across intestinal mucosa of winter flounder, Pseudopleuronectes americanus.

HUANG, K. C., AND THERESA S. T. CHEN. Ion transport acro.ss intestinal mucosa of winterjlounder, Pseudopleuronectes americanus. Am. J, Physiol. 220(6): 1734-1738. 197 1 .-Isolated winter flounder small intestine mounted in an Ussing chamber and bathed on both sides with teleost fish Ringer solution showed a PD ranging from 1 to 5 mv, with the serosa being electronegative to the mucosa. When the bathing fluid was replaced with Na$Od Ringer, both PD and I SC were reversed from negative to positive. Ion flux measurements with radioisotopes showed a net mucosal-to-serosal flux of sodium and chloride ion, but there was no net sulfate flux. The net flux of chloride ions was greater than that of Na and was sodium independent. Studies on fluid and ion movement across noneverted intestinal sacs revealed a significant loss of mucosal fluid accompanied by a decrease in both Cl and Na ions and an increase in HCO3 ion. The presence of HC03in the bathing solution was essential for optimal transmucosal transport of Cl ion. Acetazolamide at a concentration of 2 mu reduced the loss of mucosal fluid and the ion transport after a 4-hr incubation period, suggesting that the carbonic anhydrase plays a role in the transport of anions across the fish intestine.