Dual action of chloroquine on frog's skeletal muscle contraction

Studies on the effect of chloroquine on frog's rectus abdominis muscle have been performed. Relatively low concentrations of chloroquine, 5 times 10-5 and 2 times 10-4 g/ml inhibited cholinesterase activity and potentiated acetylcholine (ACh)-induced contractions but antagonized carbachol and caffeine contractions, as well as ACh-induced contractions of eserinized muscle. High concentrations (5 times 10-4 and 2 times 10-3 g/ml) non-competitively antagonized contractions to ACh, carbachol, caffeine and potassium. It was suggested that the blocking action of chloroquine was due to its local anaesthetic property and interference with intracellular calcium movements.