100 



M. A. ROTHENBERG 



VOL. 4 (1950) 



6.0 



^5.0 

 6«.0 



3.0 



2.0 



1.0 



tt 



JO 



60 



90 

 Min. of exposure 



Fig. 3. K penetration across the membrane of the 

 giant axon of Squid when exposed to 0.026 M K^^Cl 

 in artificial sea water (twice the normal K concen- 

 tration). The horizontal broken line on the ordinate 

 indicates the K*- concentration outside. The pene- 

 tration of K*^ in millimoles (mM/ioo g axoplasm 

 (wet weight) is plotted against time in minutes. 



|2A0 

 %,200 



<- 160 



^120 



80 



40 



15 30 60 90 



Min. of exposure 



Fig. 4. Rate of K penetration across the membrane 

 of the giant axon of Squid when exposed to 0.026 M 

 K-'^Cl in the artificial sea water (twice the normal 

 K concentration). The rate of penetration of K'*^ 

 in micromoles (^M)/ioo g/min is plotted against 

 time of exposure in minutes. 



o20 



10 



15 30 60 DO 



Min. of exposure 



Fig. 5. Na penetration across the membrane of the 

 giant axon of Squid when exposed to artificial sea 

 water containing either 0.13 M or 0.065 M Na^^Cl. 

 Total NaCl concentration is 0.52 M. The penetra- 

 tion of Na in millimoles (mM)/ioo g axoplasm 

 (wet weight) is plotted against time of exposure in 

 minutes. 



to those of Fig. 3. The rates of K*^ 

 penetration against time with 0.026 

 M KCl outside are given Fig. 4. From 

 a comparison of Figs 2 and 4, it is 

 evident that the initial rate of K*^ 

 penetration, using 0.026 M KCl out- 

 side, is greater than that of the initial 

 penetration rate obtained with 0.013 

 M KCl outside. Also, in the case of 

 0.026 M KCl outside, the rate of 

 penetration falls more rapidly than 

 in Fig. I. However, the limiting rate 

 of penetration finally attained is 

 twice that of Fig. 2. 



2. Sodium. The problem of Na 

 penetration into the giant axons of 

 Squid was investigated in a manner 

 similar to that employed for K*^. In this 

 case, however, either one fourth or one 

 eighth of the Na^^ in the sea water 

 (normally 0.52 M) was replaced by 

 Na-*. The remainder of the Na, neces- 

 sary for maintainence of isotonicity 

 of the sea water, was made up with 

 ordinary Na^^. All other ions were 

 maintained in their normal concentra- 

 tions. Calculation of the Na pene- 

 trating the fiber was made on the 

 assumption that there was no inherent 

 difference in the case of Na^^ and Na^* 

 penetrations. Some typical data ob- 

 tained are illustrated in Table II. 



Fig. 5 represents all of the Na 

 penetration data accumulated. It will 

 be noted that Na enters the fibres at a 

 rather high initial rate which falls 

 markedly quite quickly. The Na pene- 

 tration reaches a maximum of ap- 

 proximately 17.0 millimoles/ioo g. 

 This value is in good agreement with 

 the value of 16.2 meq. per cent (16.2 

 millimoles/ioog) calculated by Stein- 

 bach AND Spiegelman^^ from the 

 data of Webb and Young. Our value 

 for the Na penetrating would, there- 

 fore, seem to indicate that exchange 

 of Na across the nerve membrane is 



References p. 114. 



