Energetics of Sodium Transport in Frog Skin

Abstract

Studies were made of the dependence of the rate of oxygen consumption, J(r), on the electrical potential difference, Deltapsi, across the frog skin. After the abolition of sodium transport by ouabain the basal oxygen consumption was independent of Deltapsi. In fresh skins J(r) was a linear function of Deltapsi over a range of at least +/-70 mv. Treatment with aldosterone stimulated the short-circuit current, I(o), and the associated rate of oxygen consumption, J(ro), and increased their stability; linearity was then demonstrable over a range of +/-160 mv. Brief perturbations of Deltapsi (+/-30-200 mv) did not alter subsequent values of I(o). Perturbations for 10 min or more produced a "memory" effect both with and without aldosterone: accelerating sodium transport by negative clamping lowered the subsequent value of I(o); positive clamping induced the opposite effect. Changes in J(ro) were more readily detectable in the presence of aldosterone; these were in the same direction as the changes in I(o). The linearity of J(r) in Deltapsi indicates the validity of analysis in terms of linear nonequilibrium thermodynamics-brief perturbations of Deltapsi appear to produce no significant effect on either the phenomenological coefficients or the free energy of the metabolic driving reaction. Hence it is possible to evaluate this free energy.