ii6 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



procedure will decrease contamination by the incubation medium. This leads 

 to lower values for mitochondrial specific activity and hence to lower apparent 

 rates of exchange. In the centrifuged suspensions reported by Bartley and 

 Davies the inulin space was found to be about 60% and it was suggested that 

 some compartments of the mitochondria might be permeable to inulin. It is 

 equally plausible that this large value represents contamination by the suspend- 

 ing medium. 



Another difference between the two studies cited above is that Bartley and 

 Davies found that the rate of potassium exchange was the same whether in- 

 cubation was at 0° or 21° C. In the experiment shown in table 3, with mito- 

 chondria which were washed with cold saline following incubation, the temper- 

 ature of incubation had a marked effect on the rate of exchange of the residual 

 potassium of the mitochondria. 



Table 3. Effect of temperature of incubation on mitochondrial electrolyte 



For details of experimental procedure see reference (17). Incubation under aerobic con- 

 ditions for 10 minutes. Osmotic pressure of incubation medium kept constant by adjustment 

 of NaCl. Before incutiation the mitochondrial suspension contained 0.88 mEq K/gm N. 



An additional factor which complicates the determination of the actual rate 

 of electrolyte exchange between the particles and the suspending medium is 

 the fact that the absolute concentration of electrolyte in the mitochondria may 

 not remain constant during the period of incubation. In the time curve pub- 

 lished by Stanbury and INIudge (fig. 2, ref. 17), the concentration of mito- 

 chondrial potassium remained relatively stable, so that their observations on 

 exchange may be accepted as reasonable. However, it is to be noted that in the 

 experiments reported here in tables i, 2 and 3, the absolute level of mitochon- 

 drial potassium changed during incubation. When there is a net uptake of 

 potassium by the particles from a medium contaning radioactive isotope, the 

 specific activity of the harvested mitochondria will be unduly high, and false 

 values for apparent exchange rates will be obtained if the calculations assume 

 a steady chemical state. The calculations reported here can therefore be con- 

 sidered only as approximations. However, that the experimental variables ex- 



