The dependence of the electrical potentials across the membranes of the frog skin upon the concentration of sodium in the mucosal solution.

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Abstract
The dependency of the transmembranal potential differences upon the concentration [Na] of the mucosal bathing solution was investigated in frog skin. Semilogarithmic linear correlations were obtained between external concentration [Na]o and the transepithelial potential difference (slope: 28.4 .+-. 1.8 mV/dec [Na]o), the potential differences across the outer and the inner membrane under open circuit conditions (slope: 33.4 .+-. 1.8 and 4.8 .+-. 1.5 mV/dec [Na]o, respectively) and the intracellular potential under short circuit conditions (slope: 33.3 .+-. 3.4 mV/dec [Na]o). No difference could be observed between skin incubated in Cl- or SO4-Ringer. The results were not in accordance with the Koefoed-Johnsen and Ussing hypothesis. Neither the polarity of the postulated Na electrode at the outer border could be obtained nor the expected slope of the dependency between potential gradient and [Na] of the mucosal bathing solution. Current recirculation through paracellular shunt pathways was suggested to explain the deviation, at least in part. In addition, the I .cntdot. R[current resistance]-drop resulting from Na entry across the outer border might account for part of the changes of potential gradients. Under all conditions, Na uptake occurred energetically downhill, but permeability changes of the outer border must be postulated to explain the observed dependency of net Na transport upon [Na]o.