Mucosal ouabain and Na+ inhibit active Rb+(K+) absorption in normal and sodium-depleted rat distal colon.
To determine the effect of mucosal sodium and mucosal ouabain on active Rb+(K+) absorption, unidirectional and net 86Rb+ fluxes were measured under voltage-clamp conditions in the distal colon of normal and sodium-depleted rats. The role of mucosal sodium (independent of serosal sodium) was evaluated in a model of Rb+(K+) absorption in which serosal ouabain markedly enhanced active Rb+(K+) absorption. In normal rats, mucosal sodium was a competitive inhibitor of Rb+(K+) absorption, and Rb+(K+) absorption consisted of a mucosal sodium-sensitive component and a mucosal sodium-insensitive component. Further, mucosal ouabain almost completely inhibited the mucosal sodium-insensitive component but did not affect the mucosal sodium-sensitive component. In sodium-depleted rats, both mucosal sodium-sensitive and mucosal sodium-insensitive fractions of Rb+(K+) absorption were also identified. Aldosterone markedly stimulated the mucosal sodium-sensitive component (1.68 +/- 0.15 vs. 0.60 +/- 0.10 muEq.h-1.cm-2) but not the sodium-insensitive component (0.88 +/- 0.09 vs. 0.64 +/- 0.06 muEq.h-1.cm-2) component of Rb+(K+) absorption; however, in contrast to normal animals, mucosal sodium in sodium-depleted animals was a noncompetitive inhibitor of Rb+(K+) absorption. The mucosal sodium-insensitive component of Rb+(K+) absorption in sodium-depleted animals was substantially inhibited by mucosal ouabain, but the mucosal sodium-sensitive component, unlike that in normal animals, was partially inhibited by mucosal ouabain. These studies indicate that the characteristics of the Rb+(K+) absorptive process in sodium-depleted animals differ significantly from those present in normal animals, suggesting that aldosterone induces an Rb+(K+) absorptive mechanism not present in normal animals.
Pandiyan
V
V
Department of Internal Medicine, Yale University, New Haven, Connecticut.
Rajendran
V M
VM
Binder
H J
HJ
D000818:Animals; D003106:Colon / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects*; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012414:Rubidium Radioisotopes / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*
D012414:Rubidium Radioisotopes; D010042:Ouabain; D012964:Sodium; D011188:Potassium