Muscle enzymatic changes induced by blockage of axoplasmic transport

The activity of malic dehydrogenase, pyruvic kinase, and phosphorylase b was measured in the geniohyoid muscle of the cat after injection of 10 10 mM colchicine into the hypoglossal nerve. Experiments performed 1-60 days after the injection showed that the activity of the three enzymes gradually decreased (day 4-5), reached a maximum fall (day 10-25), and subsequently returned to control values (day 30-60). Concomitantly to these enzymatic alterations, the muscles showed fibrillation and ACh hypersensitivity; however, in contrast to denervation, the drug had no effect on nerve conduction, effective neuromuscular transmission, and ultrastructure of motor end plates. Experiments with [3H]colchicine indicated that the observed changes were brought about by the drug acting directly on the motor axons rather than on the muscle cells. The transsynaptic effects induced by colchicine treatment to the nerve can be ascribed to a temporary interruption of axoplasmic transport. It is suggested that neurotrophic regulation of some muscle-soluble enzymes partly depend on the normal operation of the axoplasmic transport system.