228 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



represented by the passively moving chloride ions. The resistance of the shunt 

 largely determines the value of the spontaneous skin potential. This must al- 

 ways be lower than the E^IF of the sodium transporting mechanism. Experi- 

 ments in which the voltage was maintained at different levels, for a given piece 

 of skin, showed a positive correlation between sodium outflux and skin poten- 

 tials but a negative correlation for influx as well as net flux and potential. In- 



1.0 



y = -0.0061 + 0.923 

 r 5 -0.725i P : <0.0I 



E 

 _ o 



Millivolt 



20 



40 



60 



80 



100 



120 



Fig. 14. Dependence of net chloride (NaCl) transport across skin upon sivin potential. 

 Calcium-free Ringer's solution on both sides of the skin. Rana pipiens (28). 



crease of sodium influx with increasing spontaneous skin potential was seen by 

 Fuhrman and Ussing (8). Although this type of relationship is theoretically 

 quite possible, it is somewhat puzzling, since under similar experimental con- 

 ditions Koefoed-Johnsen, Levi and Ussing (39), as well as other workers (28, 

 46), have found decreasing Cl~ influx, outflux and net flux with increasing spon- 

 taneous skin potential (fig. 14). 



The correlation between skin potential and active salt transport can also be 

 deduced from two useful equations derived by Linderholm (45) : 



