Zhong H, Guerrero S W, Esbenshade T A, Minneman K P
Department of Pharmàcology, Emory University Medical School, Atlanta, Georgia 30322, USA.
Mol Pharmacol. 1996 Jul;50(1):175-84.
We examined the role of beta 1- and beta 2-adrenergic receptor (AR) density and ratio in catecholamine-stimulated cAMP responses in rat C6 glioma cells. These cells, which normally express both subtypes, were stably transfected with an isopropylthio-beta-D-galactoside-inducible vector containing either beta 1AR or beta 2AR coding sequences, and receptor expression was controlled by the time and concentration of isopropylthio-beta-D-galactoside exposure. Induction of the dominant beta 1AR subtype increased the potencies of isoproterenol (ISO) and other agonists in stimulating cAMP accumulation by 20-40-fold without changing maximal response. Induction of beta 2AR expression caused 7-13-fold increases in the potency of ISO, epinephrine, and zinterol, but not of norepinephrine, and a 20-40% loss in maximal response to all agonists. Selective antagonists showed that both subtypes contributed in a nonadditive manner in the response to ISO under different conditions. After beta 2AR induction, the effects of ISO were not blocked by the beta 1-selective antagonist CGP 20712A but were shifted 100-fold to the right by the beta 2-selective antagonist ICI 118,551. However, in the presence of ICI 118,551, CGP 20712A caused an additional 100-fold decrease in ISO potency, and Schild analysis revealed complex interactions between the two subtypes. Each antagonist alone caused smaller shifts to the right in the dose-response curve to NE and, when present simultaneously, completely abolished the NE response. We conclude that beta 1ARs and beta 2ARs have different efficiencies in activating cAMP accumulation in C6 glioma cells. Activation of coexisting subtypes results in complex and sometimes synergistic interactions between the two subtypes, which vary with agonist concentration, selectivity, subtype density, and ratio.
我们研究了β1 - 和β2 - 肾上腺素能受体（AR）密度及比例在大鼠C6胶质瘤细胞中儿茶酚胺刺激的环磷酸腺苷（cAMP）反应中的作用。这些通常同时表达两种亚型的细胞，用含有β1AR或β2AR编码序列的异丙基硫代 - β - D - 半乳糖苷诱导型载体进行稳定转染，受体表达通过异丙基硫代 - β - D - 半乳糖苷暴露的时间和浓度来控制。优势β1AR亚型的诱导使异丙肾上腺素（ISO）和其他激动剂刺激cAMP积累的效力增加了20 - 40倍，而最大反应不变。β2AR表达的诱导使ISO、肾上腺素和齐特罗尔的效力增加了7 - 13倍，但去甲肾上腺素的效力未增加，并且对所有激动剂的最大反应损失了20 - 40%。选择性拮抗剂表明，在不同条件下，两种亚型在对ISO的反应中以非相加的方式起作用。β2AR诱导后，ISO的作用不被β1选择性拮抗剂CGP 20712A阻断，但被β2选择性拮抗剂ICI 118,551使剂量反应曲线右移100倍。然而，在存在ICI 118,551的情况下，CGP 20712A使ISO效力额外降低100倍，并且Schild分析揭示了两种亚型之间的复杂相互作用。每种拮抗剂单独作用时使去甲肾上腺素剂量反应曲线向右的移动较小，并且当同时存在时，完全消除了去甲肾上腺素反应。我们得出结论，β1ARs和β2ARs在激活C6胶质瘤细胞中的cAMP积累方面具有不同的效率。共存亚型的激活导致两种亚型之间复杂且有时是协同的相互作用，这种相互作用随激动剂浓度、选择性、亚型密度和比例而变化。
