Working with sciatic nerves from the South American frog Calyptocephalella gayi we have been able to substantiate the finding of Ungar et al., that nerve proteins undergo a reversible denaturation concomitant with a train of nerve impulses. We also showed that 0.3 mM sodium azide is capable of impairing the reversibility of those changes. Furthermore, 10 meq/liter of calcium ion applied to extracts of resting nerves induce configurational rearrangements in the proteins similar to those produced during stimulation. We also proved that nerves previously kept in low calcium Ringer's solution do not show configurational changes upon stimulation. A tentative interpretation of the results described is that the configurational changes are a consequence of the extra influx of calcium ion due to nerve impulse propagation.

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