I20 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



activity and ion transport have tempted many investigators to estimate the 

 work of transport on the basis of the energy derived from metaboUsm. The 

 present studies with DNP clearly illustrate the futility of calculating work in 

 biological systems when the discrete reactions that are involved are totally 

 obscure. For example, the rates of potassium exchange are approximately the 

 same in the control as at high concentrations of DNP, while at the same time 

 the efficiency of aerobic phosphorylation is depressed about ten fold from P/0 

 ratios of about 3.0 to ratios of 0.20. Calculations of the energetics of transport 

 in these two situations is obviously impossible in the absence of any further 

 knowledge of the mechanisms involved. 



SODIUM METABOLISM 



When the behavior of sodium is compared to that of potassium rather strik- 

 ing differences are found. The following phenomena are observed with mito- 



Table 5. Effect of external na concentration on na exchange 



Cup labelled * incubated with nitrogen in the gas phase, all others with oxygen, as pre- 

 variously described (17). Incubation for 40 minutes at 25° C. Mitochondria were prepared 

 in chilled 0.15 m/1. KCl, and after incubation were washed three times with large volumes of 

 the same solution. 



chondria that are washed after incubation, as described above. First, at con- 

 centrations of orthophosphate which reduce the mitochondrial potassium 

 concentration to about 10% of the controls, there is no demonstrable effect on 

 the level of mitochondrial sodium. Secondly, the sodium content is not affected 

 by a wide range of DNP concentrations. And, thirdly, the external concentra- 

 tions of sodium appear to have little effect on the level of mitochondrial sodium 

 or its rate of exchange. The values for sodium in table 5 may be compared to 

 those of table i for potassium. Under these conditions the washed mitochondria 

 contain about one third as much sodium as potassium and this exchanges with 

 ambient electrolyte at a much slower rate. Our findings are of interest since, 

 in contrast with many on intact cells, the level of mitochondrial sodium does 

 not change in direction opposite to that of potassium. It has not been estab- 

 lished to what extent this type of response is determined by inherent experi- 

 mental variables. These findings are again contrary to those of Bartley and 

 Davies, who reported a rather rapid rate of sodium exchange. Differences in 



