Effects of denervation and colchicine treatment on the chloride conductance of rat skeletal muscle fibers.

Membrane potentials, cable parameters, and component resting conductances were measured in extensor digitorum longus (EDL) muscle fibers from adult rats in vitro at 24 degrees C, after 15 to 18 days of denervation by nerve section, and at seven to ten days following epineural injection of 100 to 450 mug of colchicine in the peroneal nerve. The denervated muscles were paralyzed throughout the experimental period, whereas the colchicine-treated preparations showed no clinical paralysis except for the first day or two. The EDL from the untreated side served as a control. Both the denervated and colchicine-treated fibers were depolarized, showed signs of fibrillation, had tetrodotoxin-resistant potentials, and membrane resistance was increased two- to sevenfold. In the denervated fibers, mean chloride conductance GC1 dropped from a control value of 3196 to 596 mumhos/cm2 while mean potassium conductance GK showed a tendency to rise from 260 to 332 muhos/cm2. Colchicine-treated fibers while showing a similar fall in mean GC1 from 2993 to 1066 mumhos/cm2, also showed a significant fall in mean GK from 213 to 116 mumhos/cm2. It was concluded that factors transported by the microtubular system are important for the maintenance of the high resting GC1 of mammalian skeletal muscle fibers.