THE ACTION OF DECAMETHONIUM ON THE ISOLATED RABBIT LUMBRICAL MUSCLE

¹ Departments of Pharmacology and Experimental Therapeutics, University of California Medical Center, San Francisco, California
² University of California School of Medicine, Los Angeles, California

1. The actions of decamethonium and of carbachol on the isolated rabbit lumbrical muscle are described. They are divisible into two distinct phases: the first consists of a neuromuscular block of rapid onset and short duration, associated with a diminished response to direct stimulation and followed by spontaneous partial recovery; the second is a block which slowly progresses to a steady state and is not associated with an alteration in response to direct stimulation.

2. Acetylcholine produces a similar effect on a muscle which has been treated with neostigmine.

3. The first phase has many of the characteristics associated with decamethonium (in vivo) in sensitive species. The second phase closely resembles the actions of tubocurarine, including antagonism by anticholinesterases and potassium ions. The chief difference is a very much slower rate of onset of phase II block.

4. Evidence is presented that phase I is dependent upon a rate process while phase II is associated with a stationary or nearly stationary condition. The significance of these conclusions in relation to the mode of action of neuromuscular blocking agents is discussed.

5. Certain anomalous features of the action of decamethonium and related drugs on this preparation could be explained on the basis of a three-dimensional receptor mass. Such a structure would be analogous in some respects to a particle of synthetic cation exchanger.