REACTIONS OF NERVES AND MUSCLES TO RADIATION 297 



the concentration of potassium ions in the outer medium. It had been 

 shown in earlier experiments by other authors that the irreversible 

 contraction of striated muscles of the frog observed after irradiation 

 with very high doses is associated with a depolarization of the cell 

 membrane, an increased loss of potassium from the cell, an increased 

 concentration of sodium within the cells and with an increased oxygen 

 consumption (Bergeder, 1955, 1958; Bergeder and Hockwin, 1960). 



KCl belongs, together with acetylcholine, nicotine, conine and 

 veratrine, to a group of drugs, which produce a reversible contraction 

 of muscles accompanied by a loss of internal potassium and depolariza- 

 tion of the membrane. The effect of these substances can be neutralized 

 if anodic polarization is applied to the muscle. Other drugs, such as 

 chloroform, tribromethylene or lactic acid cause damage to the mem- 

 brane and irreversible contractions (Fleckenstein, 1955). The reversible 

 changes observed by us may be compared with the effect of the first 

 mentioned group of drugs and only the "residual contraction" after 

 high doses may be due to an irreversible damage of the membrane or 

 other cell constituents. 



Without going into further detail, I should like to present a model 

 which I believe explains our results : in the resting muscle fibre irradia- 

 tion produces an increased permeability which persists only during the 

 course of irradiation and for a short time thereafter. The degi-ee of 

 the permeability change is a function of the dose-rate and its duration 

 depends on the exposure time. During the time in which the per- 

 meability is changed a loss of potassium (and perhaps also of other 

 ions) from the cells takes place and equivalent amounts of sodium enter 

 the cell. In this way the quotient of the various internal to external 

 electrolyte concentrations changes and this is accompanied by a fall of 

 cell potentials and by contraction of the muscle fibres. 



Shortly after irradiation the normal permeability state is almost 

 completely restored. Due to metabolic processes ("sodium-pump") the 

 original equilibrium of the electrolyte concentration is restored and the 

 muscle relaxes. However, if the metabolic processes are inhibited the 

 origmal electrolyte concentrations cannot be restored and therefore 

 a certain degree of contraction persists. The most important question 

 now is whether radiation attacks the cell membrane directly or in- 

 directly by liberation or activation of pharmaco-active substances. 



The considerably more sensitive reaction of nerve-muscle prepara- 

 tions of the same species to X-rays have not been investigated suffici- 

 ently for discussion of the underlying mechanism. One might assume 

 though, that the nerve itself can be irritated by ionizing radiation and 

 that in this case the site of action could be the cell membrane too. 



