Inhibition of Actomyosin ATPase by High Concentrations of 5-Hydroxytryptamine. Possible Basis of Lesion in 5HT-Induced Experimental Myopathy

The effect of 5-hydroxytryptamine (5HT) on the ATPase activity and sulphydryl group reactivity of mammalian skeletal muscle actomyosin has been studied. 5HT inhibited the Mg2+-activated but not the Ca2+-activated ATPase activity of actomyosin. It slightly activated myosin ATPase. The sulphydryl groups of actomyosin reacting with 5,5'-dithiobis-(2-nitrobenzoic acid) were blocked by concentrations of 5HT which inhibited the Mg2+-activated ATPase. The significance of the results are discussed in relation to the muscle lesions in the experimental myopathy induced by 5HT and imipramine.