Energetics of Coupled Active Transport of Sodium and Chloride

Abstract

A Clark electrode was used to measure oxygen consumption by the gall bladder, in which there is a direct and one-to-one linkage between active Na and active Cl transport. O₂ uptake was reversibly depressed when Cl in the mucosal bathing solution was replaced by a poorly transported anion, such as sulfate. This effect of Cl was abolished by ouabain or in Na-free solutions. When the anion was chloride, treatment with ouabain or replacement of Na by a poorly transported cation depressed Qo_o2, more than did replacement of Cl. However, ouabain or removal of Na also depressed Qo_o2, in Na₂SO₄ solutions, in which salt transport is minimal. It is concluded that oxygen uptake in the gall bladder consists of three fractions: 9% requires both Na and Cl, is inhibited by ouabain, and is linked to the NaCl pump; 36% requires Na but not Cl, is inhibited by ouabain, and possibly is linked to the cellular K uptake mechanism; and 55% represents basal uptake. If the extra oxygen uptake observed during transport supplies all the energy for transport, then 25 Na + 25 Cl ions are transported actively per O₂ consumed; i.e., twice as many ions as in epithelia which transport only Na actively. This extra uptake is more than sufficient to supply the energy for overcoming internal membrane resistance under the experimental conditions used.