[Differential block of peripheral nerve fibers: the effect of lidocaine and potassium deficiency].

The combined effects of lidocaine and lack of glucose and potassium on conduction in A and C axons were investigated in vitro in rabbit vagus nerve. Extinction times of compound action potentials of A and C axons were determined in glucose and potassium deficient medium in the absence (group I, n = 6) or presence (group III, n = 6) of 0.1 mmol/l lidocaine hydrochloride. In group I, A fibers lost excitability within 120 +/- 9 min (mean +/- SEM) and the C axons within 133 +/- 6 min. In group III lidocaine prolonged significantly extinction times of both A and C axons (p less than 0.001); however, the conduction ceased in the unmyelinated (C) axons about 120 min later than in the myelinated (A) ones (p less than 0.05). In group II (n = 6) nerves were exposed to lidocaine for the same length of time as group I; these nerves exhibited an amplitude depression of the A and C potentials of less than 50%. In group IV, where 2 or 4 mmol/l KCl was present (n = 6 with each concentration) but no lidocaine, the extinction times decreased; the decrease was statistically significant for C axons but not for A axons. The analysis of nerve core electrolytes at the end of the exposures revealed the highest sodium and the lowest potassium contents in group III nerves. The controls (group I) contained more sodium and potassium than the nerves of group II. Thus a low concentration of lidocaine prolonged excitability in A and C axons deprived of glucose (group III).(ABSTRACT TRUNCATED AT 250 WORDS)