AJP - Renal Physiology, Vol 250, Issue 3 483-F487, Copyright © 1986 by American Physiological Society
K+ transport by rat colon: adaptation to a low potassium diet
R. L. Tannen, R. Marino and D. C. Dawson
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)
