title: K+ transport by rat colon: adaptation to a low potassium diet.
abstract: Recent studies with the isolated perfused rat kidney have demonstrated the existence of an intrinsic renal adaptation to conserve K+ in response to ingestion of a low K+ diet for 3 days. To determine whether the colon alters its K+ transport properties in a similar fashion, we measured transmural 86Rb fluxes across sheets of distal colonic epithelium under short-circuit conditions. Preliminary studies using a double-isotope technique demonstrated that 86Rb and 42K fluxes were similar; therefore 86Rb flux was considered equivalent to K+ flux. The distal half of the colon from each rat was divided into two segments, referred to as early and late distal colon. Experiments were carried out using rats fed a K+ -free, control (0.15 mmol/g), and high K+ (1.13 mmol/g) powdered diet of otherwise identical electrolyte content. Net K+ secretion (Jnet) by the early distal colon was reduced from 0.45 in the controls to -0.02 mueq X cm-2 X h-1 by a low K+ diet as a result of a decrease in serosal-to-mucosal flux (Jsm), with no change in mucosal-to-serosal flux (Jms). Conductance (GT) and short-circuit current (Isc) were unchanged. Jnet by the late distal colon averaged 0.17 in the controls and 0.01 mueq X cm-2 X h-1 with a low K+ diet, but this difference was not significant statistically. In comparison with the controls, a high K+ diet had no effect on Jnet by the early distal colon (0.48 mueq X cm-2 X h-1) but increased Jnet by the late distal colon substantially (0.77 mueq X cm-2 X h-1).(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001692:Biological Transport; D003106:Colon / Q000378:metabolism*; D004032:Diet; D004848:Epithelium / Q000378:metabolism; D008297:Male; D011188:Potassium / Q000008:administration & dosage* / Q000378:metabolism* / Q000494:pharmacology; D011197:Potassium Radioisotopes; D011868:Radioisotopes; D051381:Rats; D012413:Rubidium / Q000378:metabolism
chemical_list: D011197:Potassium Radioisotopes; D011868:Radioisotopes; D012413:Rubidium; D011188:Potassium