Myotonia Induced by Monocarboxylic Aromatic Acids

The monocarboxylic aromatic acids 2,4-dichlorophenoxyacetic acid (2,4-D) and 3-chloro-2, 5, 6-trimethylbenzoic acid, which are myotonia-inducing agents, were found to increase the K -independent p -nitro-phenylphosphatase (basic p -NPPase) activity of microsomes isolated from normal rat skeletal muscle. The activities of K + -stimulated p -NPPase and Na + ,K + -stimulated adenosine triphosphatase were unchanged. Similar findings were observed in muscle microsomes from rats made myotonic with 2, 4-D. It is proposed that increased basic p -NPPase activity is related to increased passive flux of K + and that the latter might play a primary role in producing the myotonia.