Sodium transport and distribution of electrolytes in frog skin

The objective of this study on frog skin was to examine correlations between transepidermal active Na-transport and intracellular [Na]c, [K]c, [Cl]c homeostasis. Isolated, whole skins, and "split skins" were used in measurements of short-circuit current (SCC) and open skin potential (PD). Water and ion contents were estimated on split skins. Absolute [Na]c and [K]c varied over the range of 18 to 46, and 113 to 80 mM, respectively (Figure 7), but a complementary relationship existed between Na and K, such that [Na]c + [K]c remained approximately equal to 129 mM. Average values for [Na]c and [K]c were approximately equal to 31 and approximately equal to 96 mM, respectively. [Cl]c remained constant at approximately equal to 38 mM. This complementary relationship does not seem to be an artifact, caused by collagenase, used in the preparation of split skins. Whole skins and split skins in Ringer's solution, when treated with fluoroacetate (FAc), ouabain (Ou), or vanadate (Va) over wide ranges of concentrations, showed that FAc greatly depressed the SCC and the PD, without changing [Na]c, [K]c, [Cl]c. FAc acted only from the corium side of the skin. The decreasing SCC remained a Na-current, as in control skins. By comparison, such a separation of cellular functions could not be established with Ou, or Va. These inhibitors either affected SCC, PD, and cellular ion concentration, or they had no effect on any of these parameters. The complementary relationship between [Na]c and [K]c, with [Cl]c remaining again at approximately equal to 38 mM, was also found in tissues exposed to inhibitors. These results indicate that transcellular active Na transport and electrolyte homeostasis are not always rigidly coupled, suggesting that these processes may not be uniformly distributed within the epithelial cells, or among the interconnected cell layers of the frog skin epidermis.