292 C. T. GAFFEY 



channel (Mullins, 1956). It is maintained that only whole shells of hydration 

 for ions are replacable by the membrane's wall in the process of solvation. 

 In this sense, a 3.67 A sodium ion would not "fit" into a 4.05 A potassium 

 ion channel because the quantum solvation provided by the wall of the 

 potassium ion channel does not match a sodium ion. This could be true only 

 if some level of hydration (secondary, tertiary) for sodium did uniquely 

 match some hydrated size of potassium. By similar reasoning, potassium 

 ions do not fit sodium size channels. A comparison to Bohr's theory in which 

 electrons exist in integral energy levels is only an analogy, but it may help 

 one's thinking. For the membrane's channel wall, it is held that instead of 

 an infinite number of solvation levels, there are only a restricted number 

 with properties represented by functions of n, where n is an integer. 



If the quantized view of membrane solvation is correct, and ions penetrate 

 the membrane with only the primary layer of hydration, then it will cost the 

 cell more in solvation energy to transport sodium (44.7 kcal/mole) than 

 potassium (40.5 kcal/mole) . On the evolutionary scale it would appear that 

 the cheaper ion was selected to balance the intracellular negative charges. 



The initial suggestion of a helical protein structure does not violate our 

 knowledge about the architecture of proteins. In terms of our membrane 

 model, the helical nature of protein provides a key to the interpretation of 

 the excitation phenomena of axons. Protein membrane molecules are con- 

 ceived to be in a contracted or coiled state, while the nerve is in the resting 

 state. A threshold stimulus permits the constrained, helical macromolecule 

 to become relaxed or uncocked, thus diminishing the radius of the macro- 

 molecule. Intermolecular attractive forces maintaining membrane structural 

 order cause a decrease in the mode of the channel size distribution when 

 coiled macromolecules uncock. If, on stimulation, the membrane macromole- 

 cules alter their radii from 28.2 A to 26.2 A, the new mode of the channel 

 size distribution will be 3.67 A, the size of primary hydrated sodium ion (see 

 Fig. 13, conducting state). It is naive to imagine that the helical protein 

 molecules have characteristics of a mechanical spring. A coiled spring can be 

 stretched a good deal before a decrease in radius is effected. The reduction 

 of the radical dimension of the membrane's helical molecules is perhaps due 

 to the action of London forces. 



A pleasing consequence of this membrane model is the number of neural 

 characteristics it can interpret. The all-or-none law for axons on the 

 molecular level can be viewed as the states which the membrane helical 

 macromolecules can occupy; either a stimulus is sufficient to uncock the 

 macromolecule, or it is not. If the stimulus is sufficient, the channel size 

 mode shifts from potassium to sodium and ions follow their electrochemical 

 gradient generating a bioelectric impulse. Molecularly translated, the refrac- 



