450 



The Molecular Basis of Nerve Conduction /24 : 4 



to - 117 mv the initial hump disappears and by - 130 mv a hump in 

 the opposite direction has appeared. 



By removing the Na + from the external medium and replacing it 

 with choline" 1 ", Hodgkin and Huxley showed that the initial hump was 

 due to Na + conduction. If the permeability of the membrane to Na + 



+65 



+20 



+ 10 



+ 5 



0.1 ma /cm 2 



1 0.2 mo/cm 



| Q [jl II I I II I I I I II I I J J I I ■■■ I I II II I . I 



ma /cm 2 ° l0 20 30 40 50 60 msec 



2.0 ma /cm 2 



i ii 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

 2 4 6 8 10 12 msec 



Figure 8. Further records of membrane current under a 

 voltage clamp. The displacement of membrane potential (V) 

 is given in millivolts by the number attached to each record. 

 Inward current is shown as an upward deflection. Six records 

 at a lower time base speed are given in the right-hand column. 

 Experimental details as in Figure 6. After A. L. Hodgkin, 

 A. F. Huxley, and B. Katz, "Current- Voltage Relation in 

 Nerve," J. Physiol. I 16: 424 (1952). 



suddenly increased, one would expect a hump proportional to the 

 difference between the sodium potential and the resting membrane 

 potential. The emf associated with these Na + ions is in the reverse 

 direction from the resting potential and is about 1 1 7 mv below the 

 resting potential. If due to Na + , the hump should disappear at a 

 depolarization of 1 1 7 mv, and then reverse at greater polarizations. 

 The results indicate that the sodium current can be expressed as the 





