ICHIJI TASAKI AND CONSTANTINE S. SPYROPOULOS 



217 



impedance loss during activity, however, was found to decrease with in- 

 creasing pressure even though the spike amplitude at the same pressure 

 was unchanged or increased slightly. In many respects the effects of high 

 pressure resembled the effects of low temperature. The effect of pressure 

 upon the impedance loss is illustrated in figure 9. 



The resting potential of the squid giant axon was found to be nearly 

 independent of pressure (up to 4000 psi). At pressures higher than 5000 

 psi, the measurement of the resting potential was disturbed by spontaneous 

 firing of impulses. 



The resistance of the resting membrane was found to increase slightly 

 with increasing pressure. At about 5000 psi, the increase was 10-20% of 

 the normal membrane resistance. After exposing the axon to pressures be- 

 tween 9000 and 12000 psi it was frequently observed that the membrane 

 resistance fell to one half to one third of the original value. Upon decom- 

 pression from the pressures of 9000-12000 psi the recovery of the membrane 



Fig. 9. Effect of pressure upon 

 the simultaneously recorded ac- 

 tion potential and the mem- 

 brane impedance of the srjuid 

 giant axon. The bridge A.C. was 

 10 kc/sec. Vertical bar at riglit 

 subtends 100 mv. Time marking, 

 4 msec. 



resistance was usually poor. The threshold as determined by long rectangu- 

 lar current pulses applied to the membrane through an intracellular elec- 

 trode was found to decrease very markedly with increasing pressure. At 

 pressures from 3000 to 7000 psi the threshold was reduced to zero and the 

 fiber fired spontaneously. 



EFFECTS OF TEMPERATURE AND PRESSURE ON THE NARCOTIZED AXON 



It is well known that application of narcotics reduces the height of the 

 action potential, raises the threshold membrane depolarization and de- 

 creases the membrane conductance at the peak of activity (see 30). We 

 found in the squid giant axon that these effects of narcosis can be counter- 

 acted by cooling or by application of high pressure. 



When a giant axon was immersed in a 3% ethanol-sea water solution 

 at room temperature, the spike amplitude recorded with an internal elec- 

 trode decreased by 30-50%. Frequently the size of the response was re- 

 duced to the point where it varied with the stimulus intensity. Under the 

 influence of the narcotic the threshold membrane depolarization was 



