598 DOWSE, NEUMAN, LANE, AND NEUMAN 



l:)eiDg approximatcK twice that in the phosphate liiiffer aerobiealh'. 



It is difficult to find an adequate explanation for effects of this 

 kind in\()l\ing phosphate and bicarbonate; effects which are not 

 confined to bone cells. Sexeral possibilities, however, come to mind. 

 One invohes the intracellular level of inorganic phosphate, on the 

 assumption that inorganic phosphate is one of the regulatorv factors 

 of the ghx'olytic rate. Thus, in ascites tumor cells, glycolvsis can 

 be markedh' increased b\ increasing the concentration of inorganic 

 phosphate in the mediimi and therebx', indirecth , in the cell ( Racker 

 and Wu, 1959 ) . However, though increase in phosphate ion concen- 

 tration to levels of 40 niM led to some further stimulation of glv- 

 colysis, it was not very great, and not of the order obtained with 

 ascites preparations. Also, addition of bicarbonate suppressed the 

 phosphate effect. Thus, in a medium containing both phosphate at 

 16-mM and l^icarbonate at 25-mM concentrations the Ql was almost 

 identical with tlie quantitv found in tlie standard bicarbonate- 

 buffered medium. 



We have been unable to find a difference between Qo.^ in bicar- 

 bonate-buffered medium on the one hand and phosphate-buffered 

 medium on the other using the COl- buffer technique suggested bv 

 Pardee and developed in detail by Krebs ( Umbreit et ah, 1959 ) . If 

 Warburg's "indirect" method is used, however, the Q0.2 appears to 

 be increased some threefold in the presence of bicarbonate. We can 

 suggest no explanation for the lack of agreement between the results 

 obtained with the two methods, though a \'ariable CO2 retention bv 

 the tissue, as postulated bv Borle (Borle et ah, 1960fl, 1960/?), is 

 one possibility. Until this problem can be resolved, the possible 

 effect of different oxidation rates upon glycolysis in the two media 

 cannot be determined. 



Another explanation involves control of the intracellular pH. One 

 would expect extracellular bicarbonate to exert a more efficient con- 

 trol over the intracellular pH than phosphate, because of the differ- 

 ence in permeability characteristics of the two ions. However, the 

 crucial experiment has not been devised to test this hypothesis. 

 Lactate production is only slightly affected b\' changes in the pH 

 in phosphate medium between 7.3 and 7.8; below this pH, Qi. is 

 decreased ( Fig. 2C ) . 



