Use of acute phenolic denervation to show the neuronal dependence of Ca2+-induced relaxation of isolated arteries

We recently showed that perivascular sensory nerves of mesenteric resistance arteries (MRA) express a receptor for extracellular Ca2+ (CaR) and proposed that activation of the CaR by Ca2+ causes nerve-dependent vascular relaxation. We now describe a novel procedure for acutely denervating isolated arteries and have used this method to test the hypothesis that Ca2+-induced relaxation of MRA is nerve dependent. MRA were studied using a wire myograph equipped with electrodes for electrical field stimulation (EFS) which caused sympathetic nerve-mediated contraction, and when applied in the presence of guanethidine, induced nerve-mediated relaxation. Ca2+-induced relaxation was produced by the cumulative addition of Ca2+ to MRA precontracted with norepinephrine. Exposure of MRA to 6.5% phenol in ethanol for 20 sec significantly attenuated EFS-induced contraction and relaxation, and Ca2+-induced relaxation. The magnitude of the relaxation response to EFS correlated significantly with the decrease in Ca2+-induced relaxation. In contrast, endothelium-dependent relaxation induced by acetylcholine was slightly, but nonsignificantly decreased by phenol treatment and did not correlate with Ca2+-induced relaxation. These data indicate that brief exposure of isolated MRA to phenol significantly impairs perivascular nerve function and support the hypothesis that Ca2+-induced relaxation is neurally mediated.