222 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



The middle part shows net uptake of sodium by the epithelium and net release 

 from the corium for three levels of NaCl in the saline solutions. The data refer 

 to the activity of i gm of fresh skin, which is equivalent to about 45 cm- of skin. 

 Results for net uptake and release of water are given in the lower part of the 

 figure. The upper part of the figure indicates net uptake by the corium and net 

 release from the epithelium of potassium. Extracellular potassium ion concen- 

 tration, in juEq/ml, has been plotted on the abscissa in each of the diagrams. 

 For convenience, the log scale has been chosen. 



With reference to active salt and water transport, the following can be 

 pointed out: /) negative as well as positive potassium balance in the skin itself 

 results in relatively small rates of active salt and water uptake. In other words, 

 whenever the skin loses a fair amount of potassium or accumulates an excess of 

 it, the salt transporting mechanism does not function properly. 2) Optimal rates 

 for active uptake are found under conditions of almost complete potassium 

 balance in the skin. In saline solutions of physiological NaCl level, this optimum 

 is maintained over a relatively wide range of extracellular K+ concentrations, 

 resulting in a slightly negative, a complete or a slightly positive potassium bal- 

 ance in skin. This is not the case for diluted or concentrated saline solutions. 

 Here, optimal transport rates for salt and water are reached only with a mod- 

 erately negative and a moderately positive potassium balance in skins, respec- 

 tively. 



Interesting relationships between intracellular potassium and intracellular so- 

 dium were found (29). The upper diagrams of figure 12 indicate leakage of potas- 

 sium from the inside or the outside of the skin, or uptake of potassium from the 

 outside, as the case may be. The figures plotted, designated as Q^ (potassium 

 quotient), express percentage loss or gain of intra- or extracellular potassium 

 with reference to the net amount of potassium lost into or taken up from the 

 baths. Q^" and Q"20 have similar meanings with respect to sodium and water. 

 It should be noted that related Q values for intra- and extracellular ions and 

 water were plotted from the same base line, so that the respective areas indi- 

 cated in the diagrams appear as superimposed rather than added one to the 

 other. 



Experiments with diluted saline (first vertical row of diagrams) seem to indi- 

 cate that over a wide concentration of extracellular potassium, only a small 

 percentage (5 or less) of the amount of sodium taken up by the epithelium is 

 trapped as intracellular sodium, and by far the greater portion is transported 

 across the skin. Experiments with physiological saline and with saline of higher 

 than physiological NaCl concentration, on the other hand, clearly show that at 

 low potassium levels of the baths, a large fraction of the sodium actively taken 

 up by the epithelium becomes trapped as intracellular sodium and, associated 

 with this, one observes that sodium transport across the skin is small. 



By combining the information given in figures 11 and 12, one can easily find 



