Il6 R. W. GERARD, R. W. DOTY VOL. 4 (1950) 



fluoroacetate can reduce the resting oxygen consumption below half normal while 

 leaving conduction and the attendant respiration increase intact. Resting and active 

 respiration are thus sharply separable, yet they are effectively interchangeable in support 

 of function. 



For these studies, a modified Gerard-Hartline capillary respirometer was developed. Ten 

 slots in a plexiglass block served as nerve chambers, each fitted with stimulating and lead-off elec- 

 trodes. Capillaries led from each into a large chamber machined in the same block, the whole being 

 covered with a plexiglass sheet and mounted in a glass-walled water bath. The movement of dodecane 

 indicator drops in the capillaries was followed with a horizontal microscope mounted on the compound 

 rest of an II inch lathe. Stimuli at 120/sec gave an action spike of about 25 mm measured on the 

 cathode ray tube face. 



The resting Qq^ of twenty four pairs of frog sciatics at 24° C (22 to 26) centered 

 around 65 and the two nerves of a pair agreed within 12% (aver. 4%) in all but three 

 cases. The increased Q02 on maximal stimulation averaged 21, but with an average 

 difference between members of a pair of nearly 30%. The coefficient of correlation 

 between spike height and activity Qq^ was only 0.4 for 67 normal nerves, and that 

 between resting Qq^ and the active increase, — o.i. Even allowing for methodological 

 errors, these data suggest some real independence of the three variables. 



In ten experiments with Na azide (o.i or 0.3 mM, Ph7-5, i hour soak), spike height 

 of the exposed nerves averaged 88 % of their undrugged partners, while the Q02 increase 

 on tetanization was only 12% of the normals. In four experiments with spike height in 

 both nerves of a pair alike, the Qq^ increase in the azide member was o or i. Even these 

 azide concentrations do not fully spare the resting metabolism, which was depressed by 

 o in 4 experiments to some 50% in 2. When resting oxygen was cut in two and the active 

 increase abolished, spike height was greatly reduced. Stronger azide (5 or 10 mM) cut 

 resting Q02 to 20-35% of normal and stopped conduction. Full conduction without 

 increased Q02 is possible for at least 4 hours. 



In II experiments with MFA (i to 2.5 mM), the spike height and the extra Q02 of 

 activity remained entirely normal in the exposed nerves, while the resting Q02 was 

 depressed 25% on the average, one third maximum. This depression cannot be solely 

 of non-axonal tissue {e.g., Schwann cells), for fiber thresholds rise acutely. With stronger 

 MFA (13 experiments at 5 or 7.5 mM), resting and active Q02 were both cut to about 

 half and spike height to under two-thirds normal. In individual cases, the active spike 

 and Q02 were essentially normal with resting Q02 depressed to one-third; in one case 

 activity responses remained normal for 7 hours with resting Q02 at 50%. More usually 

 with resting Qq^ cut in half the active increase was also abolished while spike height 

 remained close to normal. 



A nerve can thus continue to conduct for hours with no increase in oxygen con- 

 sumption and even with some half its resting respiration lost. Whether other energy 

 sources are being tapped or even whether the small initial heat persists without delayed 

 heat under such drug action, could be determined by heat measurements; but it seems 

 most likely that the extra energy for activity is somehow derived from the resting 

 metabolism by virtue of the considerable safety factor normally present. 



SUMMARY 



Using a modified Gerard-Hartline capillary respirometer the resting respiration of frog nerve 

 at 24° C was measured, Qog 65, as well as the increase on tetanization at 120/sec, Qoj 21, and the 



