ajmaline and Myotonia

The therapeutic effectiveness of several membrane stabilizing drugs was investigated on experimentally induced myotonia by 2,4-Dichlorophenoxyacetate (2,4-D) and in 20 patients with myotonia congenita. Procainamide and quinine showed a better antimyotonic effect in-vitro- as well as in-vivo-experiments on the cold blood muscle and the rat than Sparteine sulfate and Tachmaline (Ajmalin). The two last-mentioned drugs had nearly the same effect. Because of these experimental results only procainamide and sparteine sulfate were clinically used. Quinine was not used because of the well known side-effects. Mention is made of the fact, that the therapeutic effect depends on the dose or the concentration. The results support not only the theoretic considerations on the pathogenesis of myotonia but also recommend to carry out further pharmacological investigations with this method.

Topics: 2,4-Dichlorophenoxyacetic Acid; Adolescent; Adult; Ajmaline; Animals; Child; Electrolytes; Electromyography; Humans; Ion Channels; Membrane Potentials; Middle Aged; Myotonia; Myotonia Congenita; Procainamide; Quinine; Rana esculenta; Rats; Rats, Inbred Strains; Sparteine

Six patients with congenital myotonia and 4 patients with myotonic dystrophy have been examined clinically before and after the administration of N-propyl-ajmalin, an alkaloid frequently used as a cardiac antiarrhythmic drug. All patients but one reported a good to moderate improvement of their myotonic muscle stiffness. This was verified by measuring the time the patients needed to ascend a flight of stairs and by recording the speed of opening the hand. The amplitude of the compound muscle action potential decreased during repetitive nerve stimulation in myotonic patients. This decrease was not influenced by N-propyl-ajmalin. It seems to be due to the increased after-depolarization observed in myotonic fibres which causes partial inactivation of the Na-carrying system. From one patient a muscle biopsy was taken and intracellular potentials were measured with a microelectrode. Almost all muscle cells investigated showed myotonic activity which was completely abolished by addition of 10(-5) g/ml N-propyl-ajmalin to the bathing fluid. The development and duration of "warm-up" is illustrated and a possible electrophysiological basis is discussed.

Topics: Action Potentials; Ajmaline; Female; Humans; Locomotion; Male; Muscle Contraction; Muscles; Myotonia; Myotonia Congenita; Myotonic Dystrophy