AJP - Gastrointestinal and Liver Physiology, Vol 246, Issue 5 594-G602, Copyright © 1984 by American Physiological Society
Ion transport by rabbit descending colon: mechanisms of transepithelial potassium transport
R. D. McCabe, P. L. Smith and L. P. Sullivan
In vitro preparations of rabbit descending colon were studied under
steady-state short-circuit conditions to determine 1) the K concentration
dependence of unidirectional K fluxes; 2) the effects of the K channel
blocker barium and the diuretic agent furosemide; and 3) the steady-state
tissue specific activity of 42K when added to the luminal bathing solution.
Results from these studies reveal that 1) labeling of cellular K from the
mucosal solution is less than 25% of that from the serosal solution; 2)
both unidirectional K fluxes are composed of saturable and nonsaturable
components; 3) the serosal-to-mucosal saturable component is abolished by
ouabain, and subsequent addition of 2,4-dinitrophenol abolishes the
saturable component of the mucosal-to-serosal K flux; 4) luminal or serosal
barium alters K transport in a manner consistent with the presence of
barium-sensitive K conductances at both membranes; 5) luminal furosemide
did not alter K transport; and 6) there is no shunt selectivity for K. We
conclude that the majority of both unidirectional K fluxes follow a
transcellular pathway and that both the apical and basolateral membranes
possess active K uptake mechanisms and barium-sensitive K exit mechanisms.
