Regional variations in electrical and ion transport properties along the isolated intestine of the frog Rana esculenta.

Anterior, posterior and colon regions of isolated intestines of the frog Rana esculenta were studied in Ussing chambers under short-circuit conditions. Each region presented a serosa-positive potential which decreased upon longer incubation with no significant change in resistance. The colon displayed higher transepithelial potential (initial mean: 11.4 mV) and resistance (165.cm 2) than the proximal parts (initial mean: ca. 2 mV and 120-80 .cm 2). Bilateral substitution of Na+ by NMDG (N-methyl-D-glutamine) or of Cl- by gluconate induced large and sustained decreases in potential and current, which were reversed in the anterior and posterior intestine and abolished in colon, indicating strict dependence upon the presence of both Na+ and Cl-. The mucosal membranes showed the presence of amiloride-sensitive Na+ sites (with drug efficiency higher in colon). Na+/K+/2Cl- cotransport (current decreased by about 50% by bumetanide in anterior and posterior regions only), Cl- permeability or channels inhibited by diphenylamine-2-carboxylate, DPC (similar decreases as by bumetanide). In either chamber 5 mM BaCl2 induced 20-42% inhibition of current, indicating the occurrence of barium-sensitive K+ channels in both apical and basolateral membranes (more markedly on serosal side) in all three intestinal regions. Finally, current increase by IBMX and theophylline designate the colon as a target for adenylate cyclase stimulating hormones.