Alterations in the stability of mammalian A fibers produced by N2O and by CO2

Abstract

In an oxygen atmosphere, freshly excised r ammalian nerves exhibit a spontaneous repetitive discharge amounting to some 100 µv throughout the range 20°–35°C. This instability may be attributed to lack of CO₂ in experimental environment, since it disappeared after 5% of an atmosphere of this gas was introduced. Discharge was abolished in an identical manner if nerves were soaked for 2 hours in a nonbicarbonate buffered Ringer's solution (10 mm/l. of trishydroxymethyl-aminomethane). If under these conditions the preparation was exposed to 2–4 atm. of N₂O the instability reappeared manifested as a repetitive discharge which might exceed 200 µv. This activity arises from large diameter ‘A’ fibers, since the smaller fibers in the population are inexcitable in pressure range where instability is most prominent. In the same pressure range postspike oscillations appeared when the nerves were stimulated electrically with a maximal shock. Production of spontaneous rhythmicity and postspike oscillations by specific amounts of N₂O are believed to result from the same alteration of the neuronal membrane. Thus an increase in permeability of this structure to K may account for these findings. Mechanism of the alteration by N₂O might be found in a failure of Ca to exert its stabilizing action.