Ion transport by rabbit colon |
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Authors: | Raymond A. Frizzell Marilyn J. Koch Stanley G. Schultz |
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Affiliation: | (1) Department of Physiology, University of Pittsburgh, School of Medicine, 15261 Pittsburgh, Pa. |
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Abstract: | Summary Descending rabbit colon, stripped ofmuscularis 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 currentIsc 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 fluxesJsmi of Na, K and Cl suggest thatJsmNa,JsmK and one-third ofJsmCl may be attributed to ionic diffusion. The permeabilities of the passive conductance pathway(s) are such thatPK PNa PCl=1.0 0.07 0.11. Electrolyte transport byin vitro rabbit colon closely resembles that reported fromin vivo studies of mammalian colon and thus may serve as a useful model for the further study of colonic ion transport mechanisms. |
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