ELECTROLYTE DISTRIBUTION AND ACTIVE SALT UPTAKE IN FROG SKIN* Bx ERNST G. HUF,

Essential requirements for the maintenance of active uptake of sodium chloride in isolated frog skin in Ringer's solution are: sufficient oxygen supply (8); neutral or slightly alkaline reaction of Ringer's solution (10); a reasonable temperature, e.g. 25°C., of the environment (10). A few years ago it was found (11) that, in addition to the above mentioned factors, the K + level in Ringer's solution greatly determines the net rate of NaCI uptake. Frog skin in salt solutions from which K + was omitted showed a relatively slow average rate of NaCI uptake, McClure (25), in 1927, called attention to the fact that water transport across skin between isotonic Ringer's solutions is smaller in the absence than in the presence of potassium. The significance of potassium for the maintenance of skin potential was demonstrated by Fukuda (6). He found that removal of potassium ions from the salt solution at the inside of the skin caused disappearance of the "asymmetry potential", especially in skins of summer frogs. According to Rubin (28), frog skin, like most other tissues, contains a relatively large amount of potassium, the bulk of which, according to Rubin and Syrocke (29), can histochemically be located in the epithelial layers of the skin. Steinbach (32) was the first to study the dependence of potassium ill frog skin on the potassium concentration of the bath in which pieces of skin had been immersed for several hours. These facts, when considered together, are quite suggestive that potassium may be essentially involved in the mechanism of uptake and transport of sodium chloride and water. The experiments to be described in the following were undertaken with the aim of demonstrating, in some detail, the dependence of several properties of isolated skin on the ionic composition of the salt solution. Both the K + and the Na + concentrations of the salt solutions were varied over a relatively wide range from levels below to levels above so called physiological ion concentra-