The effect of aldosterone on the energetics of sodium transport in the frog skin

Uncertainty persists as to whether the stimulation of active sodium transport by aldosterone is attributable to effects on permeability or energetic factors. This question has been examined with the aid of a thermodynamic formulation in which the rate of both active sodium transport J_Na and O₂ consumption J_r are assumed to be linear functions of the electrical potential difference Δψ and the affinity A (negative free energy) of metabolic reaction. Previous studies have indicated constancy of a characteristic affinity on perturbation of Δψ, suggesting the possibility of its evaluation. In studies of paired frog skins the admnistration of aldosterone led to a significant increase in the short-circuit current I₀, a suggestive increase in the associated rate of O₂ consumption J_ro, and a significant increase in the ratio

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. If linearity obtains this ratio is equal to A. Depression of active sodium transport and the associated metabolism with amiloride, which depresses permeability, also results in an increase in the apparent affinity

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. The results indicate that aldosterone does not act simply by increasing the permeability or the number of transport units operating in parallel, but suggests that energetic factors are implicated as well.