130 



FACTORS AFFECTING METABOLISM in Vltro 



markedly different from the changes found with electrical stimulus. 

 Possibly some intermediate first increases in quantity before being 

 broken down to yield inorganic phosphate. Whatever the reason, 

 the experiments provide clear evidence that the increased levels of 



10 20 30 40 50 60 70 80 90 

 Time (sec) after exposing to KCL 



Fig. 16. The breakdown of phosphocreatine induced in guinea 

 pig cerebral slices by addition to the medium of 0091 M KCl. 

 (a) • = phosphocreatine; + = inorganic phosphate, slices 

 preincubated in saline containing 091 M sucrose, (b) O = 

 phosphocreatine, slices preincubated in 0045 M sucrose. Data 

 from Heald (1954), and unpublished. 



inorganic phosphate accompanying the breakdown of phospho- 

 creatine are not necessarily derived directly from it. Change in 

 phosphocreatine levels as a result of potassium stimulation may in 

 fact assume a more complex pattern than that shown in Fig. 16, 

 when changes in tonicity of the medium are also involved. Thus, if 

 slices were incubated in salines containing 90 n\M sucrose (as a 

 partial compensation for the subsequent osmotic change) and 



