Effects of m-cholinoceptor antagonists on the neuromuscular junction.
The effects of four m-cholinoceptor antagonists and d-tubocurarine on carbachol- or nicotine-induced contractions of frog rectus abdominus muscle were investigated. The n-cholinoceptor-mediated contractile responses of frog rectus abdominis muscles were inhibited competitively by d-tubocurarine whereas m-cholinoceptor antagonists inhibited them noncompetitively. Antagonistic potencies for m-cholinoceptor antagonists, assessed by pD'2 values, indicated a rank order of potency which was 4-DAMP > AF-DX 116 > atropine > pirenzepine. The antagonistic potencies of m-cholinoceptor antagonists on electrically induced twitch responses of rat phrenic nerve-diaphragm preparation were also examined. These responses were blocked by 4-DAMP, but pirenzepine had no effect. However, they were enhanced by AF-DX 116 or atropine. Inhibitory action of 4-DAMP in this preparation was suggested to be due to noncompetitive blockade of postjunctional n-cholinoceptors.
Olmez
E
E
Department of Pharmacology, Faculty of Medicine, Hacettepe University, Ankara, Turkey.
Egilmez
Y
Y
Guc
M O
MO
Ilhan
M
M
D000009:Abdominal Muscles / Q000502:physiology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D018680:Cholinergic Antagonists; D003964:Diaphragm / Q000294:innervation; D004558:Electric Stimulation; D005260:Female; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology; D009466:Neuromuscular Blocking Agents / Q000494:pharmacology*; D009469:Neuromuscular Junction / Q000187:drug effects*; D009538:Nicotine / Q000494:pharmacology; D010791:Phrenic Nerve / Q000502:physiology; D011817:Rabbits; D011898:Ranidae; D051381:Rats
D018680:Cholinergic Antagonists; D009466:Neuromuscular Blocking Agents; D009538:Nicotine; D002217:Carbachol; D002118:Calcium