Ethanol selectively affects Na+‐gradient dependent intestinal transport systems

Abstract
Moderate concentrations of ethanol reduce the velocity of uptake of three representative Na+‐symport systems (D‐glucose, L‐alanine, L‐ascorbate), whether electrogenic (the first two) or electroneutral (L‐ascorbate). This ‘inhibition’ is observed only if these transport systems are tested in the presence of an initial Na+ gradient (out > in); no inhibition is found in tracer‐equilibrium exchange measurements. A representative Na+independent system (D‐fructose) is not inhibited by ethanol. ‘Passive diffusion’ (measured as uptake of L‐glucose) is increased somewhat by alcohol. All these observations can be rationalized [as suggested by Tillotson et al. (1981) Arch. Biochem. Biophys. 207, 360–370] by an effect of ethanol on passive diffusion, which leads to a faster collapse of the Na+ gradient, with the resulting reduction of the uptake velocities of Na+‐dependent transport systems when tested with the added driving force of an Na+ out → in gradient.

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