title: Mechanism of active potassium absorption and secretion in the rat colon.
abstract: To characterize and contrast the active potassium absorptive and secretory processes present in the rat colon, unidirectional 42K fluxes were performed under short-circuit conditions across isolated distal (D) and proximal (P) colonic mucosa of control rats and animals with hyperaldosteronism due to sodium depletion (aldosterone group). In the control D colon there was net potassium absorption (+0.51 +/- 0.07 mueq X h-1 X cm-2). The absorptive process appears electroneutral because net potassium flux ( JK net ) was unchanged in sodium-free Ringer solution (+0.76 +/- 0.12 mueq X h-1 X cm-2), whereas short-circuit current (Isc) was reduced to zero, and in chloride-free Ringer solution. In P colon of controls, net potassium secretion was -0.19 +/- 0.02 mueq X h-1 X cm-2 and was abolished by removal of sodium but not by removal of chloride. In both P and D colon aldosterone produced active potassium secretion (-0.39 +/- 0.06 mueq X h-1 X cm-2, P less than 0.001, and -0.90 +/- 0.07 mueq X h-1 X cm-2, P less than 0.001, respectively) that was sodium and chloride dependent. Although mucosal amiloride in D colon of aldosterone animals reduced net sodium flux to zero and reversed Isc from 4.1 +/- 0.6 to -1.1 +/- 0.1 mueq X h-1 X cm-2, net potassium secretion was not affected. Thus, in the presence of amiloride, Isc is accounted for by JK net (-0.93 +/- 0.12 mueq X h-1 X cm-2). These data indicate that 1) the active potassium absorptive process is electroneutral and could be explained by a potassium-proton exchange, and 2) the potassium secretory process is stimulated by aldosterone, is not inhibited by amiloride, and probably is electrogenic.
mesh_terms: D000450:Aldosterone / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008297:Male; D011188:Potassium / Q000378:metabolism*; D011197:Potassium Radioisotopes; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D011197:Potassium Radioisotopes; D000450:Aldosterone; D000584:Amiloride; D011188:Potassium