CHEMOPOTENTIALS IN GIANT NERVE CELLS ^ 185 



(b) Anaerobic Transitions in the Respiratory Catalysts of the Soma 



After this brief description of some results concerning the cytochemical 

 organization of these nerve cells, we return to the question: what are the 

 biochemical events during the latency required for the anoxic inhibition of 

 the electrical activity of the cell ? 



Let us consider the 6-min latency of the more sensitive cell, the Br soma. 

 During the first 2 min of anoxia all the oxygen content in the ganglion is 

 swept out by the nitrogen. This deoxygenation time of the intrasomatic 

 oxyhaemoprotein was determined kinespectrographically by measuring the 

 density of spectrograms as a function of time (Chalazonitis and Arvanitaki, 

 1956). 



During this first phase of anoxia, the Br membrane depolarizes by about 

 2 mV, and, as already seen, the slow wave activity becomes continuous. It 

 is thus reasonable to attribute some regulatory function to the presence of 

 oxygen in the membrane's structure; that is to say, the presence of oxygen 

 is required for repolarization. 



After the exhaustion of the oxygen one must consider a second phase, at 

 least equal in duration to the former 2-min phase, during which the DPN in 

 the soma is being reduced anaerobically. The delayed reduction of the DPN 

 is evident from some in vivo and in situ kinespectrographic experiments 

 showing the delayed reduction of the cytochromes following the complete 

 deoxygenation of the oxyhaemoglobin (Arvanitaki and Chalazonitis, 1952). 

 In view of some data obtained by Chance and co-workers from different cells 

 by simultaneous polarographic and spectrophotometric measurements 

 (Chance, 1954), the delayed reduction time of the DPN in vivo could be con- 

 sidered approximately equal to that required for the complete exhaustion of 

 the oxygen. So, during this second phase of anoxia, a further production of 

 CO2 by the DPN reduction remains possible, although the formation of lactic 

 acid starts simultaneously. 



Therefore aU oscillographic events described during this second phase 

 (depolarization and changes in the frequency relating to the firing level of 

 each cell) are simultaneous with the total DPN reduction, to the final CO2 

 formation and to the incipient lactic acid production. 



As the CO2 is formed and then swept out by the nitrogen, the accumulation 

 of lactic acid on the membrane may be responsible for further depolarization. 

 In fact, extracellular application of lactic acid and of some other weak acids 

 such as succinic and citric acids on Aplysia\ somata was found to cause 

 depolarizations which are readily reversible (unpublished). 



Finally, the last 2-min anoxic phase in the Br cell preceding its inhibition 

 and all further anoxic events in the other cells are a fortiori attributable to the 

 further accumulation of products of the anaerobic glycolysis on the mem- 

 brane. 



