EXPOSURE OF THE ISOLATED FROG SKIN TO HIGH POTASSIUM CONCENTRATIONS AT THE INTERNAL SURFACE. I. BIOELECTRIC PHENOMENA AND SODIUM TRANSPORT*

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Abstract
In the present studies, the internal surface of the short-circuited isolated frog skin was exposed to potassium concentrations varying from 110 to 120 m[image]. Conventional frog Na-Ringer''s solution generally was maintained in contact with the external surface. Potential difference (P. D.) short-circuit current (S.C.C.), and electrical resistance all decreased immediately upon exposure to the high potassium solutions. P.D. typically became stable at 20% or less of the control values, electrical resistance remained low, but S.C.C. rose, and in most instances reached levels varying from 50 to 150% of control values. When isosmotic Na- and K-Ringer''s were used on opposite surfaces of the skin, net sodium influx across the skin not only persisted, but values appreciably exceeded S. C.C. The discrepancy between these two parameters was related largely to the transcellular efflux of potassium ions. Because sodium transport occurred down a steep electrochemical gradient, the process could have been entirely passive. However, during complete short-circuiting, the ratio of the unidirectional sodium fluxes (using Na22 and Na24) consistently exceeded the ratio of sodium concentrations in the bathing solutions. Furthermore, after addition of strophanthin (1.4 x 10-4 [image]), flux ratios promptly fell to approximate concentration ratios. These data are believed to demonstrate the phenomenon of "downhill" active transport The cumulative observations also may have a bearing on another aspect of active Na transport. On the basis of persistence of high values for S.C.C. in the face of a possible reversal in the normal direction of net potassium diffusion across the internal border of the epithelial cells, the possibility has been considered that the active transport of sodium may have been an electrogenic process.

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