Neurotrophic regulation of resting membrane potential and acetylcholine sensitivity in rat extensor digitorum longus muscle

In this study the effect of brief exposure of rat sciatic nerve to various concentrations of colchicine was examined. Low concentrations (4 to 15 mm) did not affect the resting membrane potential of extensor digitorum longus muscles but increased their acetylcholine (ACh) sensitivity. Intermediate concentrations (30 to 60 mm) reduced the resting membrane potential and increased ACh sensitivity. High concentrations (120 to 240 mm) impaired neuromuscular transmission in addition to reducing the resting membrane potential and increasing ACh sensitivity. The changes caused by 30 to 60 mm colchicine were not correlated with any detectable change in muscle activity and were not due to a direct effect of colchicine on muscle because muscles from the treated and contralateral sides invariably contained the same concentration of colchicine whereas changes in the resting membrane potential and ACh sensitivity occurred only on the treated side. These changes were evident in 3 days, progressed to a maximum in 5 to 7 days, and returned almost to normal 16 days after 60 mm colchicine treatment. The block of axoplasmic transport caused by 60 mm colchicine was examined and behaved in a manner consistent with the concept that it is responsible for the decrease in resting membrane potential and the increase in ACh sensitivity. The block was most severe in 1 day, had recovered considerably in 7 days, and was essentially gone 17 to 21 days after colchicine application.