FACTORS AFFECTING METABOLISM hi vitVO 129 



the absence of sodium ions of 15 mM the stimulation of oxygen 

 uptake is not obtained, if anything respiration is depressed 

 (Dickens and Greville, 1935; Tsukada and Takasadi, 1955). The 

 increased respiration is also not due to changes in the tonicity of 

 the medium, since addition of equimolar or greater amounts of 

 sodium salts is without effect (Dixon, 1949; Mcllwain and Gore, 

 1952). Under anaerobic conditions, increased potassium salts 

 depress lactic acid production (Ashford and Dixon, 1935; Mc- 

 llwain, 1953). With cortical slices respiring in an oxygenated 

 saline containing glucose and eserine, potassium salts increased the 

 quantities of free acetyl choline in the medium (Mann et al., 1939). 

 The effect of potassium salts is confined to nervous tissue or tissue 

 having a well-developed nervous plexus, for slices of kidney, testis 

 and liver were unaffected by 100 mM KCl (Dickens and Greville, 

 1935). It also seems that for the response the tissue must be 

 intact. Instances where the potassium salts are effective in 

 increasing the oxygen uptake in dispersions are probably due to 

 the stimulation of phosphoenol pyruvate-adenosine diphosphate 

 transphosphorylase in a system where levels of adenosine triphos- 

 phate are low (Boyer et al., 1942). 



Thus, to a large degree, increasing the quantities of potassium 

 salts in the medium produces changes in oxygen and glucose 

 consumption in cerebral tissues similar to those induced by applied 

 electrical impulses. These similarities extend to phosphate 

 metabolism. Thus, 100 mM KCl decreased levels of phospho- 

 creatine from 1-5 /^moles/g wet wt. to 0-5 /xmoles/g, at the same 

 time increasing levels of inorganic phosphate by 1-0/xmoles/g. 

 However, under these conditions the time course of phospho- 

 creatine breakdown differs from that induced by electrical pulses. 

 When slices were incubated in salines containing an additional 

 83 mM NaCl, phosphocreatine levels were maintained at 

 1-5 jLtmoles/g wet wt. On transferring to salines containing normal 

 sodium levels but an additional 90 mM KCl, levels of phospho- 

 creatine fell rapidly for the first 10 sec and thereafter more slowly 

 until the change was complete in 60 sec (Fig. 16). In contrast, 

 during this period the levels of inorganic phosphate were little 

 affected and increased only after 20-30 sec. Although a rate of 

 breakdow^n slower than that obtained with electrical pulses may 

 well be a reflection of the rate of entry of potassium ions into the 

 slice, the delay in the increase in levels of inorganic phosphate is 



