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 fr og Rana esculenta were studied in Ussing chambers under short-circuit conditions. Each region presented a serosa-positive potential which de creased upon longer incubation with no significant change in resistanc e. 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 NMD G (N-methyl-D-glutamine) or of Cl- by gluconate induced large and sust ained decreases in potential and current, which were reversed in the a nterior and posterior intestine and abolished in colon, indicating str ict dependence upon the presence of both Na+ and Cl-. The mucosal memb ranes showed the presence of amiloride-sensitive Na+ sites (with drug efficiency higher in colon), Na+/K+/2Cl(-) cotransport (current decrea sed by about 50% by bumetanide in anterior and posterior regions only) , Cl- permeability or channels inhibited by diphenylamine-2-carboxylat e, DPC (similar decreases as by bumetanide). In either chamber 5 mM Ba Cl2 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. Fina lly, current increase by IBMX and theophylline designate the colon as a target for adenylate cyclase stimulating hormones.