126 FACTORS AFFECTING METABOLISM itl Vttro 



junction with the data of Fig. 15 suggest that phosphocreatine may 

 be regarded as a sensitive indicator of the extent of oxidative 

 phosphorylation in the intact tissue. Use has been made of these 

 findings in analysing the effects of certain depressants and anti- 

 convulsants upon cerebral metabolism in vitro (Chapter 5). 



Electrical Pulses and Disintegrated Preparations 



It was noted above that preparations of cerebral mitochondria 

 or disintegrated preparations of whole tissue, showed no respira- 

 tory response to electrical stimuli applied in apparatus which 

 yielded such a response with intact tissue. In a series of papers the 

 effects of pulses upon cerebral homogenates and mitochondria were 

 described (Abood, Gerard and Ochs, 1952; Abood, 1954; Abood 

 and Romanchek, 1955; Abood, Gerard and Tschirgi, 1952; 

 Abood, 1956) from the results of which the following conclusions 

 were drawn — (a) Electrical pulses increase the rate of oxygen 

 uptake by cerebral homogenates, but having done so this effect 

 cannot be repeated once the pulses have been switched off. (b) 

 Electrical pulses decrease the rate of oxidative phosphorylation in 

 preparations of cerebral mitochondria ; this latter effect is reversible, 

 phosphorus/oxygen ratios which decrease in the presence of pulses 

 return to normal when the pulses are switched off. (c) The 

 decreased levels of phosphocreatine found in cerebral tissues 

 following electrical stimulus is more probably due to a decreased 

 rate of synthesis than to an increased rate of breakdown (see 

 however p. 116). However, Narayanaswami and Mcllwain (1954) 

 were unable to demonstrate any effect of electrical pulses upon 

 oxidative phosphorylation with dispersions of cerebral tissue or 

 with preparations of cerebral mitochondria. Although differences 

 in behaviour may perhaps be expected between cell-containing and 

 cell-free systems the two sets of results with cell-free preparations 

 clearly do not agree. Major differences exist both in the manner of 

 applying the pulses and in the composition of the electrodes. Thus 

 respiratory response with dispersions was obtained with an 

 arrangement of electrodes which would include only a few per 

 cent of the dispersion (cf. Abood and Romanchek, 1955) imposing 

 a severe limitation on the quantity of material exposed to the 

 electrical field at any one time. No information was given describ- 

 ing the effects of the arrangement upon oxygen uptake in the 

 absence of tissue dispersion. Such points are of importance since 



