AFFINITY OF CURARE-LIKE COMPOUNDS AND THEIR POTENCY IN BLOCKING NEUROMUSCULAR TRANSMISSION

¹ Department of Pharmacology, University of California at Los Angeles, Los Angeles, California

External electrodes were employed to measure the depolarization produced in various muscles of the guinea pig and the affinities of tubocurarine and other antagonists for cholinergic receptors in neuromuscular junctions were estimated. Diaphragm, serratus anterior and latissimus dorsi muscles were used; the depolarizing drugs were carbachol, decamethonium and acetylcholine and the antagonists were tubocurarine, dimethyl tubocurarine, gallamine, c-toxiferine and l-curarine. The affinities of these antagonists were compared with their neuromuscular blocking action. For any one antagonist the affinity for cholinergic receptor was similar for different muscles and when measured by means of different agonists. On diaphragm muscle the pharmacologic potency increases with affinity. Diaphragm needed more antagonist than latissimus dorsi for 50% paralysis, the ratio being 2 for d-tubocurarine to 4 for l-curarine. The concentration of antagonist required for 50% neuromuscular block was greater than the dissociation constant (estimated concentration for 50% occupancy of receptors in the absence of agonist), and the ratio in diaphragm was 3 for d-tubocurarine and for c-toxiferine, with different values for gallamine and dimethyl tubocurarine.

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