Role of glucose or potassium lack in nerve block

Potassium and glucose are usually lacking in solutions employed for nerve conduction block. The significance of this for impulse conduction was studied in rabbit vagus nerve in vitro, incubated for 2 h Ringer's bicarbonate solution containing or lacking 5 mM glucose and 4 mM potassium chloride (n = 5 for each conditions). The c-fiber actin potential was recorded by periodic stimulation and the Na and K content of the desheathed nerve core was determined at the end of the incubation. In the presence of glucose, apparently normal conduction persisted for at least 2 h, even though the nerves incubated in potassium-free medium lost 20 per cent of their potassium. In the absence of glucose, reversible extinction of conduction was complete in 78 +/- 9 min when external potassium was present, and in 110 +/- 10 min when external potassium was absent. The data suggest that lack of glucose may reinforce C-fiber inexcitability during conduction block and that inclusion of a physiologic amount of potassium chloride in the solution may also be desirable.