VOL. 4 (1950) 



PERMEABILITY AND NERVE FUNCTION, I 



91 



the height of the potential is markedly depressed in presence of eserine. The duration 

 of the descending phase is considerably prolonged. This effect of eserine on the end plate 

 potential is consistent with the assumption that 

 the appearance and the removal of acetylcholine 

 within the post-synaptic membrane may be essen- 

 tial for the generation of the potential. 



In view of their corresponding biochemical and 

 bioelectrical findings, Fessard and Nachmansohn 

 decided then to test whether acetylcholine injected 

 into the electric organ may produce an action 

 potential. Such an electrogenic effect might be 

 expected if acetylcholine is the compound which is 

 responsible for the alterations of the membrane, 

 occurring during the discharge. In experiments 

 carried out at Arcachon in 1939 on Torpedo mar- 

 mot ata, in which they were joined by Feldberg, 

 they were able to demonstrate that acetylcholine has an electrogenic effect'^' '*. The 

 arterial injection of acetylcholine caused potential changes similar to the natural dis- 

 charge. However, the changes were small and slow and very large amounts were neces- 

 sary for the effect. Fig. 4 illustrates the effects of acetylcholine injected in amounts 

 varying between 5 and 200 //g. 5 jjg had no effect. With 200 //g the potential difference 

 was about 0.7 millivolts and the descending phase had not yet reached the base line 

 after several seconds. If the acetylcholine is injected in presence of eserine, preventing 

 a too rapid destruction of the ester, the effects are greatly enhanced. Fig. 5 shows that 

 under these conditions an effect may be obtained even with 2.5 //g of acetylcholine. 

 With 10 /<g the potential change produced is greater than 3 millivolts, although the 



duration is still about 3 seconds. 



Fig. 3. Effect of eserine on the dis- 

 charge of electric tissue of Torpedo 

 marmorata. The fully drawn line shows 

 the discharge in absence, the dotted 

 line in presence of eserine^. 



I ' ^ J. L 



m 



T 



Fig. 4. Potential changes produced by 

 intraarterial injection of acetylcholine into 

 the electric organ of Torpedo marmorata. 

 I, II, IV and V correspond to the injection 

 of 200, 100, 20 and 5 /<g of the ester; 

 whereas at III only perfusion fluid was 

 injected. Between II and III the sensi- 

 tivity has been increased fourfold. 0.5 

 millivolt indicated at I, o.i millivolt at 

 IV. Time in seconds. 



Fig. 5. Potential changes produced in the 

 same way as in Fig. 4 but in presence of 

 eserine. I, II and IV correspond to the injec- 

 tion of 10, 5 and 2.5 /ig of acetylcholine; at 

 III only perfusion fluid was injected. 0.5 

 millivolt indicated at II. Time in seconds. 



The experiments show that the ester may produce an alteration of the membrane 

 preceding the flow of current. They support the view that the ester plays an essential 

 role in the generation of the current and make it difficult to assume that the release of 

 References p. 93I95. 



