Ion transport by rabbit colon. I. Active and passive components.
Descending rabbit colon, stripped of muscularis externa, absorbs Na and Cl under short-circuit conditions and exhibits a residual ion flux, consistent with HCO3 secretion, whose magnitude is approximately equal to the rate of active Cl absorption. Net K transport was not observed under short-circuit conditions. The results of ion replacement studies and of treatment with ouabain or amiloride suggest that the short-circuit current ISC is determined solely by the rate of active Na transport and that the net movements of Cl and HCO3 are mediated by a Na-independent, electrically-neutral, anion exchange process. Cyclic AMP stimulates an electrogenic Cl secretion, abolishes HCO3 secretion but does not affect the rate of Na absorption under short-circuit conditions. Studies of the effect of transepithelial potential difference on the serosa-to-mucosa fluxes Jism of Na, K and Cl suggest that JNasm,JIsm and one-third of JCl-sm may be attributed to ionic diffusion. The permeabilities of the passive conductance pathway(s) are such that Pk:PNa:PCl= 1.0:0.07:0.11. Electrolyte transport by in vitro rabbit colon closely resembles that reported from in vivo studies of mammalian colon and thus may serve as a useful model for the further study of colonic ion transport mechanisms.
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
D001639:Bicarbonates; D002712:Chlorides; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D000242:Cyclic AMP; D011188:Potassium