HIGH ENERGY IRRADIATION: BIOELECTRIC EFFECTS 289 



K* 

 Macromolecule 



Fig. 10. Protein macromolecules are schematically represented as circles oriented 

 hexagonally. At the junction of 3 macromolecules, an interstice is formed which in 

 the three-dimensional model would be a channel. Drawn to scale it can be seen that 

 potassium with its primary layer of hydration fits the channel created by the 

 macromolecules. 



considered to be larger than potassium ions, because sodium ions orient more 

 layers of hydration due to the intense electric field created by the charge on 

 the ion (Ling, 1952, 1957). Potassium ions with a lower energy of hydration 

 than sodium have effectively fewer oriented shells of hydration and hence a 

 higher mobility in an aqueous medium. Kortum and Bochris (1951) p>oint 

 out that for cations, water molecules on the first layer (primary hydration) 

 are held so tightly that the primary hydration shell moves as a unit with the 

 ion. However, water molecules beyond the primary hydration layer are 

 loosely oriented and exchange readily with surrounding water molecules. 

 Hence, it is an acceptable hypothesis that ions with one layer of hydration 

 migrate through neural membranes. From Fig. 11 it is seen that the radius 

 of primary hydrated potassium is 4.05 A which is larger than primary hy- 

 drated sodium (3.67 A in radius; Fig. 12) . The crystal lattice radii are taken 

 from Pauling (1945), and the width of concentric water shells of hydration 

 is that of the diameter of a water molecule, 2.72 A (Buswell and Rodebush, 

 1956). 



The intermolecular forces between protein elements of the membrane are 

 no doubt subjected to lateral straining pressures produced by thermal motion 

 (kinetic and vibrational) and cytoplasmic streaming. As a consequence, a 

 channel is never a fixed size, but statistically distributed, probably in a 

 Gaussian fashion. The mode of the channel size distribution of the resting 

 neural membrane is assigned to the ion empirically known to have the high- 



