146 PHYSIOLOGICAL TRIGGERS 



the specific properties of the cell membrane, manifested by its high resistivity, 

 'pump' action, and ion selective behavior. Electrogenic activity develops when 

 the cell membrane is responsive to stimuli, reacting by alteration of its ion 

 permittivity. This transducer action is probably specifically determined by 

 membrane molecular configurations of as yet unknown nature. Certain of these 

 configurations probably respond only to specific stimuli, while others may be 

 excited by several varieties. In some cells the membrane appears to be composed 

 of several transducer types. Junctional systems in general appear to have 

 specialized chemo-transducer membrane at the synaptic sites of the post- 

 junctional cell. These respond to transmitter agents (some of which are now 

 known) released during activity of the pre-junctional cell. They give rise to 

 specific types of transducer action in the postsynaptic membrane and specific 

 electrogenic activity determined by the nature of the transducer response and 

 the electrochemical state of the post-junctional cell. This electrogenic response, 

 the postsynaptic potential, if depolarizing may by its local circuit action in turn 

 serve as a stimulant to electro-transducer membrane neighboring the chemo- 

 transducer type. The resultant electrical response may have an explosive char- 

 acter, derived from the regenerative restimulation of the electro-transducer by 

 the altered membrane polarization. Explosive responsiveness permits all-or- 

 nothing, decrementless propagation of information for long distances in the cell. 

 On the other hand, membrane transducers insensitive to electrical stimuli are 

 capable of electrogenic responsiveness graded in amplitude and duration with 

 the intensity and duration of the stimulus, but rapidly losing intelligibility 

 with distance of propagation in the cell. The combination of graded and all-or- 

 nothing responses developed by the simultaneous presence of different types of 

 transducer membrane may have a functional significance in junctional trans- 

 mission. 



The occasion of this symposium reenforces a grateful acknowledgment for the pleasant 

 and, to the author, stimulating discussions with Professor Otto Loewi during many summers 

 at the Marine Biological Laboratory. 



The researches of the author's laboratory on which this paper is based have been carried 

 out with a number of collal)orators, and were supported in part by funds from the following 

 sources: American Philosophical Society (Penrose Grant 1880); Atomic Energy Commission 

 (AT 30-1 1076); Marine Biological Laboratory (ONR contract Nonr 09703); Muscular 

 Dystrophy Associations of America; National Institute of Neurology and Blindness (B-389); 

 National Science Foundation; Process and Instruments, Inc.; United Cerebral Palsy Associa- 

 tions. 



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4. Altamirano, M., C. W. Coates and H. Grundfest. J. Gen. Physiol. 38: 319, 1955. 



