[Myotonic effects of 2,4-Dichlorphenoxyacetate (2,4-D) on the isolated frog skeletal muscle (author's transl)].

2,4-Dichlorphenoxyacetate (2,4-D) produces myotonic reactions not only in mammalian skeletal muscles but also in muscles of cold blooded animals. There was induced a myotonic reaction by 2,4-D on isolated frog skeletal muscle and the changes of mechanogramm and electromyogram were studied. The relaxation of contraction was prolonged about 40% when the muscle was 5 min in a solution with 3 mMol 2,4-D and the muscle was stimulated with an impulse of 1 Hz (Fig. 1 and 2). There was only a slight increase in the amplitude of the mechanogram. A higher stimulation frequency clearly showed the warm-up phenomenon. The amplitude of electromyogram increased during tetanic stimulation (Fig. 3). Finally we found also myotonic discharges when the muscle came into contact with 2,4-D (Fig. 4). All the actions induced by 2.4-D were reversible. These changes of mechanogram and electromyogram induced by 2,4-D were interpreted as a variation of the Ca++-kinetic in sarcoplasmatic reticulum and as an alteration of the sarcolemma. We interpreted the difference to the findings on mammalian skeletal muscle as a variation in metabolism between warm- and cold-blooded animals.