Reciprocal potentiating action of depolarizing drugs on the isolated frog rectus abdominis muscle.

Subthreshold concentrations of the depolarizing agents, acetylcholine and decamethonium, potentiated isotonic contractures of the isolated frog rectus abdominis muscle elicited by effective doses of either of these drugs or by choline in the absence of the anticholinesterases, sarin, or dyflos. Comparable potentiation of the contracture produced by decamethonium or choline could be obtained by alternate stimulation with acetylcholine in the absence of dyflos or sarin. Furthermore, dyflos alone did not effect potentiation in the absence of alternate stimulation with acetylcholine. Finally, the inhibitory action of tubocurarine, as measured by depression of the contracture elicited by decamethonium and acetylcholine, was not antagonized by sarin. It was concluded that the enhancement of the response to acetylcholine produced by dyflos and by sarin was brought about exclusively by their action as inhibitors of cholinesterase. The ability of dyflos and of sarin to potentiate contractures elicited by decamethonium or by choline may be attributed to a facilitation of the action of the depolarizing compounds by subthreshold concentrations of acetylcholine available in the presence of these anticholinesterases.