no M. A. ROTHENBERG VOL. 4 (1950) 



The values for the Qiq for K and Na exchange obtained, 1.22 and 1.33 respectively, 

 are in good agreement with the value of 1.25 calculated theoretically from ionic conduc- 

 tively measurements. These figures do not support the assumption that important energy 

 yielding reactions are involved in the transport of ions across these nerve membranes 

 in resting condition. Krogh discusses the possibility that the extrusion of Na from the 

 cell interior is an active process requiring energy. In support of this hypothesis, he cites 

 experiments of Harris^^ and Danowski^^ with rabbit and human erythrocytes in which 

 it had been shown that, at low temperature and at body temperature in the absence of 

 glucose, K is lost to the bathing medium and replaced by Na. When glycolysis is restored, 

 the normal K balance is restablished, even in vitro, with a resumption of rapid Na 

 extrusion. If the extrusion of Na is an active process in the nerve preparation tested, 

 under resting condition, one would have expected to obtain a larger value for the Q^q. 

 Lowering the temperature of these nerves by ten degrees should have produced a marked 

 effect on the glycolytic processes and should have been expected to yield larger Na values 

 than those obtained. 



The fact that in resting condition no expenditure of energy seems to be required 

 for the ionic movements does by no means preclude the possibility that under other 

 conditions these movements may require energy. It appears likely that during the 

 early growth stage of these nerves chemical reactions are in operation which are respon- 

 sible for the establishment of the large concentration gradient between the potassium 

 inside the fibre and that in the outer bathing fluid. The same is true for the disequilibrium 

 observed after activity. The extra oxygen uptake observed after activity indicates that 

 energy yielding reactions are involved in the restoration of the resting condition. 



The present studies of the ion exchange occurring in nerve during activity have 

 indicated that the Na content increases markedly. Similar results have been obtained 

 with muscle tissue by Fenn et al. on frog, and rat^"' 2^' ^^, Wood, Collins and Moe on 

 dog gastrocnemius^^, Tipton on cat muscle^*, Heppel on K-deprived rats^^ and Hahn 

 AND Hevesy on rats^*. All of these investigations show that in contracting muscles 

 the permeability to ions is increased. K is lost from the fibres and is replaced by Na. 

 Steinbach and Spiegelman^ have demonstrated that the cation molarity of the Squid 

 axoplasm is, under a variety of conditions, constant at rest. It appears, therefore, 

 justifiable to assume that during nerve activity K loss is compensated for by the pene- 

 tration of an equivalent quantity of Na into these fibres. 



This idea is supported by the demonstration of the penetration of 4.5 •lO"^^ mole 

 Na/cm^/impulse, a value which is in close agreement with the value of 1.7 •lO"^^ mole 

 K/cm^/impulse found by Hodgkin and Huxley^ and 2.1 -10"^^ mole K/cm^/impulse 

 reported by Keynes^". The value reported here indicates that during activity a con- 

 siderable increase of Na inside takes place. 6.4 millimoles per 100 g were found after 

 30 min stimulation at 100 per second as compared with 1.3 millimoles per 100 g at rest. 

 If an equivalent amount of K has leaked out, 21% of the total K content has been 

 exchanged during this stimulation period. It should be noted here that the period of 

 stimulation employed is by no means the maximum possible with these nerves. Much 

 more prolonged periods of stimulation at 100 per second are possible and one would 

 expect an even greater ion exchange. It should be borne in mind that the above changes 

 are completely reversible and cessation of stimulation should result in restoration of 

 the normal balance. From the above considerations, it may be concluded that, even 

 though 90% of the K content of the nerve is not exchangeable at rest, during activity 

 References p. 114. 



