Antagonism of Ca2+-induced constriction of isolated rabbit ear artery by nitrendipine in high K+- and/or norepinephrine-containing medium.
Nitrendipine is a Ca2+ channel antagonist with vasodilator and antihypertensive properties. In the present experiments, the isolated rabbit ear artery was perfused with Ca2+-free Krebs-bicarbonate solution. Constriction of the artery was induced by addition of Ca2+ to perfusion fluid in the presence of KCl (75 mM, high K+), norepinephrine (NE) at various concentrations, or high K+ and NE. Nitrendipine produced concentration-dependent inhibition of the constrictor response to Ca2+ in high K+ medium. NE, added to high K+ medium, reversed the inhibitory effect of nitrendipine. In NE-containing medium, nitrendipine also inhibited the constrictor effect of Ca2+. Nitrendipine-induced inhibition was inversely proportional to the concentration of NE in the medium. The inhibitory effect of nitrendipine in the medium containing high K+ and NE was significantly less pronounced than in normal K+- and NE-containing medium. The experiments demonstrate relative resistance of "receptor-operated" channels to nitrendipine and suggest that under depolarizing conditions these channels may operate more effectively.
D000818:Animals; D001158:Arteries / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004423:Ear / Q000098:blood supply*; D005260:Female; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009568:Nitrendipine; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D014661:Vasoconstriction / Q000187:drug effects*
D002121:Calcium Channel Blockers; D009568:Nitrendipine; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine