Structure-linked latency of muscarinic receptors in axonal transport

Muscarinic receptors that accumulated above a ligature in rat sciatic nerves were labelled in vitro under isotonic conditions with N-[3H]methylscopolamine. The addition of 0.005% of digitonin doubled the binding in proximal segments above and close to the ligature but not in the intermediary segments between two ligatures. Osmotic shock and freeze-thawing treatments also enhanced the binding. Digitonin did not affect the affinity of muscarinic receptors but revealed a greater number of sites by increasing the membrane permeability to the hydrophilic ligand. We conclude that presynaptic muscarinic receptors that undergo fast axonal transport in rat sciatic nerves exist under a latent form because they are associated with vesicles. This is the first demonstration of a structure-linked latency for receptors.