High vascular tone of mouse femoral arteries in vivo is determined by sympathetic nerve activity via α1A- and α1D-adrenoceptor subtypes.

Determining the role of vascular receptors in vivo is difficult and not readily accomplished by systemic application of antagonists or genetic manipulations. Here we used intravital microscopy to measure the contributions of sympathetic receptors, particularly α1-adrenoceptor subtypes, to contractile activation of femoral artery in vivo. Diameter and intracellular calcium ([Ca2+]i) in femoral arteries were determined by intravital fluorescence microscopy in mice expressing a Myosin Light Chain Kinase (MLCK) based calcium-calmodulin biosensor. Pharmacological agents were applied locally to the femoral artery to determine the contributions of vascular receptors to tonic contraction and [Ca2+]i,. In the anesthetized animal, femoral arteries were constricted to a diameter equal to 54% of their passive diameter (i.e. tone = 46%). Of this total basal tone, 16% was blocked by RS79948 (0.1 µM) and thus attributable to α2-adrenoceptors. A further 46% was blocked by prazosin (0.1 µM) and thus attributable to α1-adrenoceptors. Blockade of P2X and NPY1 receptors with suramin (0.5 mM) and BIBP3226 (1.0 µM) respectively, reduced tone by a further 22%, leaving 16% of basal tone unaffected at these concentrations of antagonists. Application of RS100329 (α1A-selective antagonist) and BMY7378 (α1D-selective) decreased tone by 29% and 26%, respectively, and reduced [Ca2+]i. Chloroethylclonidine (1 µM preferential for α1B-) had no effect. Abolition of sympathetic nerve activity (hexamethonium, i.p.) reduced basal tone by 90%. Tone of mouse femoral arteries in vivo is almost entirely sympathetic in origin. Activation of α1A- and α1D-adrenoceptors elevates [Ca2+]i and accounts for at least 55% of the tone.

确定血管受体在体内的作用是困难的，通过全身性应用拮抗剂或基因操作不易实现。在此我们利用活体显微镜技术来测量交感神经受体，特别是α1 - 肾上腺素能受体亚型，对体内股动脉收缩激活的作用。 在表达基于肌球蛋白轻链激酶（MLCK）的钙 - 钙调蛋白生物传感器的小鼠中，通过活体荧光显微镜测定股动脉的直径和细胞内钙（[Ca²⁺]i）。将药物局部应用于股动脉以确定血管受体对紧张性收缩和[Ca²⁺]i的作用。 在麻醉动物中，股动脉收缩至其被动直径的54%（即张力 = 46%）。在这种总的基础张力中，16%被RS79948（0.1 µM）阻断，因此归因于α2 - 肾上腺素能受体。另外46%被哌唑嗪（0.1 µM）阻断，因此归因于α1 - 肾上腺素能受体。分别用苏拉明（0.5 mM）和BIBP3226（1.0 µM）阻断P2X和NPY1受体，使张力进一步降低22%，在这些拮抗剂浓度下，16%的基础张力未受影响。应用RS100329（α1A选择性拮抗剂）和BMY7378（α1D选择性拮抗剂）分别使张力降低29%和26%，并降低[Ca²⁺]i。氯乙基可乐定（1 µM，对α1B - 有选择性）没有作用。消除交感神经活动（六甲铵，腹腔注射）使基础张力降低90%。 小鼠体内股动脉的张力几乎完全源于交感神经。α1A - 和α1D - 肾上腺素能受体的激活升高[Ca²⁺]i，并至少占张力的55%。