The Relationship of Sodium Uptake, Potassium Rejection, and Skin Potential in Isolated Frog Skin

Abstract

1. Isolated surviving frog skin, when bathed with the same kind of diluted Ringer's solution on both sides, shows a negative correlation between net active salt uptake by the epithelium and spontaneous skin potential. Average values of 0.15 to 0.86 µeq. x hr.–1 x cm.–2 were measured and correlated with average skin potentials ranging from 107 to 25 mv. 2. Sodium uptake exceeded chloride uptake by about the same amount, irrespective of the height of the skin potential. 3. The same skins which exhibited a negative correlation between net uptake of sodium chloride and skin potential showed a positive correlation between net potassium rejection from the epithelium and skin potential, for voltages above 30 to 40 mv. In skins of voltages lower than this, potassium ions were taken up rather than rejected. Average values for rejection of +11.8 to –0.8 centi-µeq. x hr.–1 x cm.–2 were measured. 4. Net fluid uptake, associated with active uptake of sodium chloride, was small and occurred in the direction of the salt uptake. No dependence of net fluid uptake upon skin potential was observed. 5. Skins of winter frogs, pretreated with a commercial purified ACTH preparation, were less active than their respective controls with regard to uptake of sodium chloride. Rejection of potassium was the same in treated and untreated skins. Posterior pituitary factors, as possible contaminants, did not account for the effect of the ACTH preparation. 6. DOCA, DOC, and cortisone did not alter the normal correlation referred to under (1) and (3). 7. In interpreting the experimental results on theoretical grounds, it is suggested (a) that in normal skin, it is the variation in the electric conductance in skin of chloride ions which essentially, although not exclusively, determines the rate of net uptake of sodium chloride, (b) that a factor in the ACTH preparation used, possibly ACTH itself, may have lowered the electric conductance in skin of sodium ions either truly or apparently, (c) that potassium ions are treated by the skin primarily as passive ions. There is some indication that potassium ions are also actively taken up by the epithelium of skin.

K+-permeability of the outer border of the frog skin (R. temporaria)

“…Huf and Wills [5] reported that K § is ejected into the epithelial bathing solution at transepithelial potentials above 30 40 mV (corial side positive). Similarly, Levi and Ussing [7] found that K § fluxes deviate from simple passive behavior and suggested that part of this flux occurs by way of a transcellular pathway.…”

Frog skin epithelium: Electrolyte transport and chytridiomycosis

“…With the lack of evidence that Bd has any direct effect on other tissues, with the exception of inhibiting Na + transport across the skin, could hypokalemia be caused by Bd increasing skin K + secretion? Although the apical membrane of the frog skin is considered to be almost exclusively permeable to Na + (Koefoed-Johnsen et al, 1952), K + permeability (Nagel and Hirschmann, 1980) and K + secretion (Huf and Wills, 1953) of this tissue has been reported. In Rana temporaria , the apical membrane became permeable to K + only after absorption of Na + was inhibited (Nagel and Hirschmann, 1980), suggesting that K + secretion is augmented by the reduction in the cytosolic concentration of Na + .…”

Active transepithelial potassium transport in frog skin via specific potassium channels in the apical membrane

“…Frog skin, toad bladder, and mammalian descending colon have been shown to secrete K' under open circuit conditions (Huf & Wills 1953, Frasier & Vanatta 1971, Edmons 1967. But it is unclear from these studies, whether the K+ secretion can be attributed entirely to simple diffusion 1: Fig.…”