FACTORS AFFECTING METABOLISM in VltVO 



Time (sec otter cessation of pulses) 



125 



30 60 90 



Time i sec after cessation of pulses)] 



Fig. 15. The resynthesis of phosphocreatine in guinea pig 

 cerebral slices after depletion by electrical pulses passed for 

 differing times. (A) pulses passed for 7-10 sec only. (B) pulses 

 passed for 20 min. In both (A) and (B) the dotted lines represent 

 the levels of phosphocreatine before passing pulses. Data from 

 Heald (1954). 



switching off the pulse. If the increased oxygen uptake ceases 

 immediately pulses are stopped, then the oxygen uptake of 

 unstimulated slices of guinea pig brain being 55 /xmoles/g hr~^, a 

 rate of phosphocreatine resynthesis of 150/xmoles/g hr"^ repre- 

 sents a phosphorus/oxygen ratio of 1-35. If the increased rate of 

 oxygen uptake continues at lOOjumoles/g hr"^ the phosphorus/ 

 oxygen ratio becomes 0-75. These values are of an order similar 

 to those found for oxidative phosphorylation in brain dispersions 

 and with mitochondrial preparations (Table 13) and taken in con- 



