Effects of adenosine and calcium entry blockers on 3,4-diaminopyridine-induced rhythmic contractions in dog coronary artery.
3,4-Diaminopyridine, a potassium (K+) channel blocker, was used to induce phasic contractions in an isolated K+-contracted dog left anterior descending coronary artery ring preparation. The effects of adenosine, N6-L-phenyl-isopropyl-adenosine (L-PIA) and 5'-N-ethylcarboxamide-adenosine (NECA) were compared with those of calcium (Ca2+) entry blockers (nifedipine, verapamil, diltiazem) on the maximum developed force, minimum developed force and contraction frequency in this model. Adenosine, L-PIA and NECA significantly relaxed the minimum force and decreased the contraction frequency without any effect on the maximum force. The order of potency was: NECA greater than L-PIA greater than adenosine. Nifedipine, verapamil and diltiazem significantly relaxed the maximum force and increased the contraction frequency without a significant relaxing effect on minimum force. It is, therefore, likely that adenosine (and its analogs) and Ca2+ entry blockers have different mechanisms for the relaxation of coronary smooth muscle and that adenosine probably relaxes the vessels through A2 receptor.
Nakazawa
M
M
Department of Pharmacology, School of Medicine, East Carolina University, Greenville, NC 27834.
Mustafa
S J
SJ
D015761:4-Aminopyridine / Q000031:analogs & derivatives*; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology*; D019830:Adenosine-5'-(N-ethylcarboxamide); D000077770:Amifampridine; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004110:Diltiazem / Q000494:pharmacology; D004285:Dogs; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010660:Phenylisopropyladenosine / Q000494:pharmacology
D000631:Aminopyridines; D002121:Calcium Channel Blockers; D010660:Phenylisopropyladenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); D015761:4-Aminopyridine; D004110:Diltiazem; D000241:Adenosine; D000077770:Amifampridine