On the oscillatory decay of the myotonic action of 9-anthroic acid. Influence of cholinesterase inhibition.
The effects of the myotonic agent, 9-anthroic acid (ANCA), and the acetylcholinesterase (AChE) inhibitor, soman, on the isolated phrenic nerve--diaphragm preparation of the rat have been studied. ANCA induced after-contractions which followed the twitches evoked by either direct or indirect stimulation. In the intermittently stimulated muscle the height of the after-contractions decreased rather rapidly and in an oscillatory fashion. The maximum height of each after-contraction was attained after the twitch had reached its peak. AChE inhibition changed the shape of these after-contractions in the indirectly, but not in the directly stimulated diaphragm. After AChE inhibition, the after-contractions decreased more slowly and in a non-oscillatory manner. Similar phenomena were observed in vivo in the gastrocnemius--soleus muscles. The effects of ANCA in the AChE-inhibited and in the non-inhibited diaphragm could be mimicked by incubation in low chloride media. Addition of ouabain to the non-inhibited diaphragm treated with ANCA, caused an immediate and striking enhancement followed by a rapid loss of the after-contractions, whereas the twitches remained fairly constant. In the AChE-inhibited diaphragm treated with ANCA, ouabain caused no increase but only a rapid and complete decay of the after-contractions with a decrease of the twitches. It is suggested that after inhibition of the AChE in the ANCA-treated muscle fibre, the site of initiation of the repetitive action potentials which cause the after-contractions shifts from the transverse tubular system to the motor end-plate. Moreover, it is suggested that the sodium pump is involved in the gradual decay of the myotonic action of ANCA.
D000818:Animals; D000873:Anthracenes / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002264:Carboxylic Acids / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D002800:Cholinesterase Inhibitors; D003964:Diaphragm / Q000187:drug effects / Q000378:metabolism; D004347:Drug Interactions; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism; D008297:Male; D009045:Motor Endplate / Q000187:drug effects / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects*; D009469:Neuromuscular Junction / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism; D012999:Soman / Q000494:pharmacology
D000873:Anthracenes; D002264:Carboxylic Acids; D002712:Chlorides; D002800:Cholinesterase Inhibitors; D010042:Ouabain; D012999:Soman; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium