Action of mefloquine on toad isolated rectus abdominis muscle

The effects of mefloquine and quinine on acetylcholine-induced contractures of the toad rectus abdominis muscle have been investigated. Both drugs depressed acetylcholine-induced contractures in a dose-related and non-competitive manner. A partial reversal of the block was observed in the presence of 4-aminopyridine (10, 50 microM) and increased Ca2+ content (1.25x) of the Ringer solution. In both cases, the mefloquine-induced blockade was more readily reversed than that induced by quinine. Mefloquine and quinine at concentrations greater than 100 and 500 microM, respectively, also elicited a direct contractile response on the muscle. Quantitative differences in their contractile activity have been attributed to the greater lipid solubility and tissue binding affinity of mefloquine.