Differential effects of vasodilators on the mobilization of calcium pools during contractions of rabbit ear artery induced by noradrenaline and high potassium

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Abstract
The effects of some vasodilators on the mobilization of different Ca2+ pools during contractions produced by noradrenaline and high K+ medium in rabbit ear artery has been investigated. Sodium nitrite was much more effective in antagonizing high K+‐stimulated Ca2+ fluxes through the potential‐dependent Ca2+ channels than noradrenaline‐induced mobilization of intracellular Ca2+ stores or Ca2+ fluxes through receptor‐operated channels. Papaverine was only slightly more active on contractions sustained by influx of extracellular Ca2+ (through potential‐dependent channels and receptor‐operated channels) than on those sustained by intracellular Ca2+. Verapamil and nifedipine were much more effective in antagonizing contractions sustained by Ca2+ entry through potential‐dependent channels than through receptor‐operated channels. Nifedipine was completely ineffective in antagonizing noradrenaline‐induced mobilization of intracellular Ca2+ stores while verapamil had a limited inhibitory action in high concentrations. Phentolamine was equieffective in antagonizing both types of noradrenaline‐induced contractions while having no effect on high K+‐induced tonic contraction.