Autoradiography of 14C-choline uptake in endplates and skeletal muscle of mice.

The uptake of 14C-choline into the axonal part of the motor endplate and muscle of mouse diaphragms was investigated by autoradiography. With i.v. doses of 0.1 microgram/g choline chloride, the uptake into the nerve endings is fast (less than 2 min) and into muscle slower (greater than 2 min). With higher doses (1.0 microgram/g) the uptake into muscle tissue is accelerated. The radioactivity in the endplates decreases with a halflife time of 20 min and remains constant in the muscle fibres over 60 min. Denervation by cutting the phrenic nerve reduces the uptake into endplates by 40% within 14 h, but probably induces uptake into regenerating Schwann cells during 30 days. Som compounds with choline-like structure (hemicholinium-3, decamethylen-dicholine, triethyl-choline) reduce the high-affinity uptake of choline into the nerve endings with sublethal doses, whereas tetraethylammonium and N-hydroxyethyl-4-(1-naphthylvinyl)-pyridinium, an inhibitor of cholinacetyltransferase, are less active. Half lethal doses of cocaine, imipramine and reserpine have no significant action on uptake of choline into the endplates. Chlorpromazine slightly diminishes the uptake into endplates. Chlorpromazine and imipramine reduce uptake into the muscle fibres.