FACTORS AFFECTING METABOLISM in vitro 127 



components of the saline can give rise to spurious increases in 

 oxygen uptake owing to oxidation at the electrodes (Lewis and 

 Mcllwain, 1954). Thus the results with homogenates might be 

 taken to imply either a greater response of the particles within the 

 electrode field or interaction of the particles with contaminants 

 released from the electrodes. This latter seems not unlikely for 

 oxidative phosphorylation was inhibited when pulses were applied 

 from electrodes originally described as silver, but actually con- 

 sisting of sterling silver (a silver-copper alloy), and was not in- 

 hibited when electrodes of pure silver, platinum or carbon were 

 used (addendum in Abood, 1954), suggesting that the previous 

 results were due to artifacts caused by the electrode material. 

 Heavy metals are known to alter the efficiency of oxidative phos- 

 phorylation in preparations of cerebral mitochondria (Clowes and 

 Keltch, 1951; Chapell and Greville, 1954). With electrodes of 

 pure silver the latter authors found that the passage of electrical 

 pulses released silver ions to the saline and increased the activity 

 of mitochondrial adenosine triphosphatase. This in turn increased 

 the amount of inorganic phosphate present and produced an 

 apparent inhibition of oxidative phosphorylation. Electrodes of 

 gold or molybdenum had no such effect. Although silver ions were 

 claimed to be without effect upon the oxygen uptake of cerebral 

 dispersions (Abood et al., 1952) addition of silver nitrate at 

 10" 5-10" ^M decreased oxidative phosphorylation in cerebral 

 mitochondria (Chapell and Greville, 1954). Addition of agents 

 capable of binding heavy metals also abolished any effects of 

 pulses from sterling silver electrodes upon oxidative phosphoryla- 

 tion (Abood and Romanchek, 1955). There is thus ample scope 

 for considering the inhibition of oxidative phosphorylation in such 

 systems to be due not to electrical pulses but to artifacts. This 

 might be considered not to apply to the supposed effect of electrical 

 pulses in bringing about a reversible inhibition of oxidative 

 phosphorylation even though the electrodes were of sterling silver 

 (Abood, 1954). The evidence for this does not appear convincing, 

 being presented as a graph of four points, the standard deviations 

 of which are not given. If such deviations were similar to those 

 given in a table of phosphorus/oxygen ratios in the same paper, 

 the apparent variations of the graph would seem to be of no 

 significance. When the uptake of radioactive phosphate was 

 measured in various fractions of mitochondrial suspensions 



