A comparison of the actions of 4-aminopyridine, caffeine and quinine on the toad isolated rectus abdominis muscle.
1. 4-Aminopyridine (4-AP)-induced contractures have been compared with those evoked by caffeine and quinine on the toad rectus abdominis muscle. 2. All three compounds produced slowly-developing sustained contractures. The time to half maximal contracture and relaxation was significantly longer for 4-AP than for caffeine or quinine. 3. Verapamil and manganese inhibited 4-AP, caffeine and quinine-induced contractures. 4. Ca2+-free-EGTA Ringer and procaine severely inhibited caffeine and quinine responses, but 4-AP contractures were relatively unaffected. 5. In depolarizing (100 mM K+) Ringer solution, caffeine and quinine responses were reduced to 6-9% of their controls. 4-AP responses were reduced by about 25%. 6. It is concluded that in the toad rectus muscle, 4-AP-induced contractures differ from those produced by caffeine and quinine, and appear to rely mainly on the release of intracellular located Ca2+, while caffeine and quinine are considered to act predominantly on plasma membrane sites.
Savage
A O
AO
Department of Pharmacology and Therapeutics, College of Medicine, University of Ibadan, Nigeria.
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D002025:Bufonidae; D002110:Caffeine / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D008345:Manganese / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011343:Procaine / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology
D000631:Aminopyridines; D009467:Neuromuscular Depolarizing Agents; D002110:Caffeine; D008345:Manganese; D011343:Procaine; D004533:Egtazic Acid; D011803:Quinine; D015761:4-Aminopyridine; D014700:Verapamil; D011188:Potassium