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 Ω·cm2) than the proximal parts (initial mean: ca. 2 mV and 120–80 Ω·cm2). 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 b...