POTASSIUM EXCHANGE IN PERFUSED MUSCLE— RENKIN 



33 



10 



. 9 



2 8h 



3- 





/ 



/ EXP. 46-B 



EXP. 61-B 

 3^0 



1 



100 200 300 400 



TIME, MINUTES 



Fig. 1. — Loss of potassium by tissues of the perfused cat hindleg. 



of intact, resting man at a comparable rate, 0.005 per cent per minute, and suggested 

 that it may be due to diurnal variations in potassium balance. 



At low temperatures, 3° to 9° C, net loss of K" was markedly decreased. In the 

 experiment illustrated (fig. 1), the loss was only 0.004 per cent tissue K"^ per minute 

 at 3°. In six hours of perfusion at this temperature, only 1.2 per cent of total tissue 

 K" was lost, in contrast to a loss of more than 50 per cent in one hour for rat 

 diaphragm soaked in Krebs' saline at 2° C* 



In experiments at normal and at low temperatures, the equilibration of tracer K''- 

 between perfusion fluid and perfused tissues was studied. Arterial radioactivity was 

 measured continuously with a recording ratemeter. The experiments could not be 

 run long enough for isotopic equilibrium to be reached, and in calculating equilibra- 

 tion kinetics it was assumed that all tissue K* is exchangeable. The equilibration 

 curves followed a double-exponential course, one possible interpretation of which 

 is that plasma K"^ equilibrates with two independent compartments of tissue K"^. 

 Table I has been prepared on this assumption, and lists compartment sizes and cal- 

 culated "exchange rates" at high and low temperatures. Since only 2 per cent of 

 tissue K^ is extracellular, both components must represent subdivisions of intra- 



