Entry of decamethonium in rat muscle studied by autoradiography.

1. When a steady plasma level of decamethonium was maintained by infusion in rats, the labelled compound became concentrated in the region of the end-plate of skeletal muscle, as shown by scintillation counting.2. The distribution of tritium-labelled decamethonium in single muscle fibres was studied by autoradiography of frozen sections, with resolution less than 1 mu.3. After intravenous injection of a dose of decamethonium which produced partial paralysis it was shown that the labelled compound had entered muscle fibres in the region of the end-plate, and for several hundred microns on either side of the end-plate.4. Entry of decamethonium could be demonstrated as early as 30 sec after intra-arterial injection. There was no evidence of any redistribution of labelled drug for a period of 2 hr after the initial entry.5. Previous administration of tubocurarine markedly reduced the entry of labelled decamethonium.