314 C. EYZAGUIRRE 



Judging by the repolarization level of orthodromic discharge and by the 

 magnitude of the inhibitory potential they concluded that the resting potential 

 increased during the appHcation of a K+-free solution, and that the inhibitory 

 potentials increased even more (Fig. 22). Since, in the absence of K+ the 

 resting membrane potential is much farther from the potassium equilibrium 

 potential than in its presence, an increase in the difference between the 

 membrane potential level and the inhibitory equilibrium level in the absence 

 of potassium is consistent with the assumption that the membrane potential 

 during the inhibitory process is more dependent upon K+ distribution than 

 at rest. 



wm 



'^M. 



Fig. 22. Effect of K+ deficiency on the inhibitory potential in the relaxed pre- 

 paration and during stretch. Extracellular d.c. recording a and c. Inhibition in 

 normal solution, b. Inhibition in K+-free solution showing the increase in size 

 of the inhibitory potentials in the absence of K+ ion. Voltage calibration 0- 1 mV. 

 Time, 0- 1 sec. (From Edwards and Hagiwara, J. Gen. Physiol. 43 : 315-321, 1959.) 



Very recent work has shown that Cl~ ions are also involved in the inhibitory 

 process of crustacean sensory nerve cells, as was suggested earher by Kuffler 

 and Eyzaguirre (1955). Jn fact, Hagiwara et al. (1960) have been able to 

 show that replacing glutamate for Ch in the bathing solution produces a 

 shift of the inhibitory reversal potential in a depolarizing direction. This shift 

 is not accompanied by resting membrane potential changes as shown in 

 Fig. 23. The change in baseline is only produced by a diffusion potential 

 between normal and glutamate sahne. These recent experiments bring into 

 focus a former observation reported by Kuffler and Eyzaguirre (1955) who 

 observed a reversal of the inhibitory potential while a cell was impaled with 

 a KCl-filled microelectrode. In this case the inhibitory potential grew pro- 

 gressively in a depolarizing direction which eventually produced a propagated 

 action potential. Apparently Cl~ ions leaked from the electrode thus loading 

 the cell with this particular anion. Furthermore, Hagiwara et al. (1960) have 



