DAVID NACHMANSOHN AND IRWIN B. WILSON 



tein, but no information is at present available about the nature 

 of the storage form. During activity, as is well established ex- 

 perimentally, acetylcholine is released from the bound form. 

 The free acetylcholine acts upon a receptor, the acetylcholine 

 receptor, and this action is responsible for the change of perme- 



ELEMENTARY PROCESS 



... 



GLUCOSE 



2 ATP 



>v^ ANAER 



2 PYRUVIC + Oj 

 VIA CITRIC ACID CYCLE 



30 ATP 



OBIC 



J 



2 LACTIC 



PHOSPHOCREATINE 



Co A ♦ ACETATE 



"V^ 



^/ 



AT 

 POOL 



ACETYL - Co A 



AMP -f PP 



Fig. 1. Sequence of energy transformations associated with conduction, 

 and integration of the acetylcholine system into the metabolic pathways of the 

 nerve cell. The elementary process of conduction may be tentatively pictured 

 as follows: 



(7) In resting condition acetylcholine (O-j) is bound, presumably to a 

 storage protein (S). The membrane is polarized. 



(2) ACh is released by current flow (possibly hydrogen ion movements) 

 or any other excitatory agent. The free ester combines with the receptor (R), 

 presumably a protein. 



(3) The receptor changes its configuration (dotted line). This process 

 increases the Na ion permeability and permits its rapid influx. This is the 

 trigger action by which the potential primary source of EMF, the ionic con- 

 centration gradient, becomes effective and by which the action current is 

 generated. 



(4) The ester-receptor complex is in dynamic equilibrium with the free 

 ester and the receptor; the free ester is open to attack by acetylcholinesterase 

 (E). 



(5) The hydrolysis of the ester permits the receptor to return to its 

 original shape. The permeability decreases, and the membrane is again in 

 its original polarized condition. 



634 



