Na and Cl transport and short-circuit current in rabbit ileum

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Abstract
Summary Na and Cl fluxes and short-circuit current (I sc) in rabbit ileum have been studied as a function of ionic concentrations in HCO3-free solutions. Both net Na flux (J Nanet ) andI sc show similar saturation functions of [Na] at fixed [Cl]. They show no significant difference between zero and 112mm Na but at 140mm NaI sc is significantly greater than theJ Nanet . Net Cl transport, secretion, is observed only at 140mm Na and is approximately equivalent to the difference between theI sc andJ Nanet . The transcellular mucosa-to-serosa Na fluxes measured at 140 and 70mm Na do not differ significantly from the correspondingI sc. The net Cl flux varies with [Cl] at fixed [Na] whileI sc is virtually not affected by [Cl]. These results suggest that the absorptive Na transport process is electrogenic and responsible for theI sc and that the secretory fluxes of Na and Cl are coupled, require high [Na], vary with [Cl], and do not contribute toI sc. K-free solution abolishes theI sc after a prolonged lag. Finally, the effect of a low resistance shunt pathway on active Na absorption is examined with a four-compartment model.