title: Potassium transport by rabbit descending colon, in vitro.
abstract: Studies of the bidirectional fluxes of K across segments of rabbit descending colon indicate that: a) when the tissue is short-circuited, the net flux does not differ significantly from zero under control conditions and in the presence of aldosterone; and b) the bidirectional fluxes of K conform to the Ussing flux-ratio equation over a wide range of transepithelial electrochemical potential differences. These and other findings strongly suggest that the movements of K across the epithelium are restricted to paracellular routes and are entirely passive. Studies dealing with the mechanism of homocellular K transport indicate that: a) K is actively transported into the cells across the basolateral membranes against an electrochemical potential difference of approximately 30 mV; and b) the active uptake of K may be mediated by a rheogenic Na-K exchange pump that is also responsible for transcellular Na transport. These results are entirely consistent with the model proposed by Koefoed-Johnson and Ussing for isolated frog skin.
mesh_terms: D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D001693:Biological Transport, Active; D002463:Cell Membrane Permeability; D003106:Colon / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism
chemical_list: D007473:Ion Channels; D000450:Aldosterone; D012964:Sodium; D011188:Potassium