GILBERT H. MUDGE 121 



experimental techniques have not been re-examined. However, the difference 

 which was reported by these authors, in the degree to which sodium- and potas- 

 sium-exchange depends on metabohsm requires further evaluation since in 

 their experiments the external potassium concentration was about ten times 

 greater than that of sodium. 



The hydration of mitochondria has been reported to be partially conditioned 

 by aerobic metabolism (i, 7). This warrants further study particularly because 

 similar phenomena have been observed in intact cells (10). 



SUMMARY 



Many questions remain totally unanswered concerning the behavior of 

 electrolytes in the mitochondria. Does the potassium, or sodium, adhere to the 

 external membrane? Or to the internal ridges? Or is it to be regarded as more 

 or less in free solution in the interior? The actual concentration of electrolyte 

 in the mitochondria of intact cells remains unknown. 



Can any special role be assigned to the electrolytes of mitochondria in regulat- 

 ing the electrolyte balance of the whole cell? Cetainly there is no direct evi- 

 dence on this point at present. The spatial orientation of mitochondria within 

 the cells of the kidney tubule make it tempting to speculate that they serve some 

 special function in transport. A fact of primary importance to this problem is 

 that the major energy yielding reactions of the cell can be attributed to the 

 metabolism of the mitochondria. If, as has been shown to be the case for a 

 variety of cells, the normal electrolyte composition of the cell is also related 

 to these same metabolic events, what then is the nature of this relationship? 

 Either the metabolic activity of the mitochondria could determine the local 

 compositions within these units which in turn might determine the composi- 

 tion of the rest of the cell; or, the electrolyte level within the mitochondria 

 might be merely an incidental phenomenon, quite unrelated to ion transport 

 across the cell membrane or through the rest of the cytoplasm. Since the results 

 obtained with isolated particles are so overwhelmingly determined by the con- 

 ditions of the experiment, there seems little justification to select between these 

 possibilities at the present time. This review has attempted to emphasize prob- 

 lems of methodology and for the time being lets go by default any tacit chal- 

 lenge to integrate these findings in terms of cell function. 



REFERENCES 



1. Bartlev, W. and R. E. Davies. Active transport of ions by subcellular particles. Bio- 

 chem. J. 57: 37-49, 1954- 



2. Claude, A. Fractionation of mammalian liver cells by differential centrifugation. II. 

 Experimental procedures and results. J. Ex per. Med. 84: 61-89, 1946. 



3. Harman, J. W. Studies on mitochondria. II. The structure of mitochondria in relation 

 to enzymatic activity. Exp. Cell. Research, i : 394-402, 1950. 



4. Hunter, F. E., Jr. Oxidative phosphorylation during electron transport. Phosphorus 



