Sodium transport across the isolated epithelium of the frog skin

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Abstract
1. A method to separate the epithelium from the underlying layers of the frog skin is described. The method is based on the combined use of collagenase and hydrostatic pressures.2. The potential difference and the short‐circuit current values of isolated epithelia and whole skins are similar. Na net flux and short‐circuit current are equivalent.3. The time course of changes in potential following rapid changes in composition of the bathing solutions shows that the barrier to K diffusion at the internal surface of the isolated epithelium is larger than the barrier to Na diffusion at the external surface.4. In the isolated epithelium there are 133 m‐mole K+ and 24·7 m‐mole Na/l. cellular water. The amount of extracellular water was considered to be equal to the inulin space.5. Arginine vasopressin (0·1 u./ml.) markedly increased short‐circuit current and potential difference in isolated epithelia. The amount of Na in the epithelium that equilibrated with Na in the external solution was not increased by the hormone.6. Ouabain (10−4 M) reduced short circuit current and potential difference to values close to zero. The ouabain treated epithelia contained an increased amount of Na originating in the internal solution. On the other hand the amount of Na that originated from the external solution was not increased.7. The amount of epithelial Na that equilibrated with Na in the external solution was 0·009 μ‐equiv/cm2. This figure is about ten times smaller than the values found in whole skins.