Energetics of Sodium Transport in Frog Skin

Abstract

Studies were made of the dependence of the rate of oxygen consumption, J , on the electrical potential difference, A,, across the frog skin. After the abolition of sodium transport by ouabain the basal oxygen consumption was independent of /x. In fresh skins J, was a linear function of Alk over a range of at least --70 my. Treatment with aldosterone stimulated the shortcircuit current, Io, and the associated rate of oxygen consumption, Jro, and increased their stability; linearity was then demonstrable over a range of 4-160 mv. Brief perturbations of A4 (30-200 my) did not alter subsequent values of 10. 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 I0; positive clamping induced the opposite effect. Changes in Jo were more readily detectable in the presence of aldosterone; these were in the same direction as the changes in I0. The linearity of J. in A& indicates the validity of analysis in terms of linear nonequilibrium thermodynamics-brief perturbations of A#p 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.

Nonequilibrium Thermodynamic Analysis of the Coupling between Active Sodium Transport and Oxygen Consumption

“…4 and Table III show that a block of Na transport by removal of Na from the external solution induces a subsequent increase in JA and J,, when Na is returned to the external solution. This behavior, and the previous results of Vieira et al (19), (showing that accelerating Na transport by negative clamping lowers the subsequent value of Io and positive clamping induces the opposite effect) could be interpreted according to Eqs. A-1 and A-2, as a result of an alteration of the phenomenological coefficients LN,r and L, or of the affinity of the metabolic driving reaction or both.…”

“…Essig and Caplan (6) have proposed a theoretical model for the active transport of a single cation coupled to a chemical reaction. The adequacy of this model to sodium transport was partially tested by Vieira et al (18) (19) in the skin of the frog Rana pipiens. They have shown that there is in short-circuited state a linear relationship between the rates of sodium transport and oxygen consumption, and that the rate of oxygen consumption is a linear function of the transepithelial electrical potential difference.…”

“…A-1 and A-2, the active transepithelial sodium transport (JNa) and the related oxygen consumption J,*o (total oxygen consumption minus basal oxygen consumption) are linear functions of the two related forces, the negative transepithelial sodium electrochemical potential difference (XN,) and the affinity of the metabolic driving reaction (A). XN is easily controlled in the experiments by proper values of the electrical potential difference and sodium concentration difference across the skin; on the other hand, A is not accessible to experimental control and may be evaluated only in some cases (19).…”

“…Considering the coupling of Na transport and oxygen consumption shown in these experiments and the linear dependence of oxygen consumption with the electrical potential difference across the skin in Rana pipiens (19), we may assume that the rate of sodium transport could also be a linear function of the electrical potential difference across the skin. In the toad bladder, Saito et al (14) have shown a linear dependence of the rate of active sodium transport on the electrical potential difference.…”

“…It was also shown that antidiuretic hormone stimulated and ouabain depressed both the rates of sodium transport and oxygen consumption; in both cases apparent stoichiometric ratios were preserved. In their second paper, Vieira et al (19) were able to show a linear dependence of the rate of oxygen consumption on the electrical potential difference across the skin over a range of +-160 mV. It was also shown that perturbations of the electrical potential difference for 10 min or more produced a "memory" effect: Accelerating sodium transport by negative clamping lowered the subsequent value of Na transport; positive clamping induced the opposite effect.…”