Simultaneous determination of beta-1 and beta-2-adrenergic receptors in tissues containing both receptor subtypes.
Simultaneous determination of beta-1 and beta-2-adrenergic receptors in tissues containing both receptor subtypes.
复制标题
同时测定含有两种受体亚型的组织中的 β-1 和 β-2-肾上腺素能受体。
作者：
K. Minneman;L. Hegstrand;P. Molinoff
一种测定含有β-1和β-2受体亚型的组织中β-1和β-2肾上腺素能受体的相对浓度和性质的方法已经建立起来。由于(125I)-碘羟基苄基pindolol对β-1和β-2肾上腺素能受体具有相似的亲和力，因此可以通过(125I)-碘羟基苄基pindolol特异性结合的Scatchard分析来确定组织中β-肾上腺素能受体的总浓度。在GTP存在的情况下，非β-1或β-2肾上腺素能受体特异性的激动剂和拮抗剂对大鼠心脏、肺和大鼠脑五个区域特异性(125I)-碘羟基苄基pindolol结合的抑制产生线性Hofstee图，Hill系数约为1.0。另一方面，体外对心脏（β-1）和肺（β-2）受体具有不同亲和力的药物对特异性(125I)-碘羟基苄基pindolol结合的抑制导致这些组织中的非线性Hofstee图。其中两种药物（普罗托尔和美托洛尔）对β-1的作用比β-2受体更强，其中两种药物（zinterol和salmefamol）对β-2的作用比β-1受体更强。非线性Hofstee图与在每个组织中存在两种类型的结合位点对药物具有不同的亲和力相一致。每种结合位点的相对数量和每种药物对这两种位点的亲和性已经使用基于计算机的迭代程序计算出来。用该方法测定两种受体亚型在大鼠心脏、肺、大脑皮层、尾状核、小脑、海马和间脑中的相对百分比。在每个组织中，使用四种体外选择性不同的药物（两种β-1选择性和两种β-2选择性），计算出的β-1/β-2比值大致相同。这表明非线性Hofstee图仅由两个分量组成的假设是正确的。此外，每种药物对β-1和β-2受体的计算亲和力在检测的7种组织中都是定量相似的。β- 1:β-2肾上腺素能受体计算比值为：心脏83:17；肺15:85;皮层81:19;尾状76:24;小脑15:85;海马体81:19;间脑71:29。在被检测的大脑区域中，β-1-肾上腺素能受体的绝对浓度几乎变化了20倍。然而，β-2-肾上腺素能受体的绝对浓度变化小于3倍。这表明β-2-肾上腺素能受体在大鼠脑中与比β-1-肾上腺素能受体更均匀分布的细胞元件相关。
A method for determining the relative concentrations and properties of β-1 and β-2-adrenergic receptors in tissues containing both receptor subtypes has been developed. Since (125I)-iodohydroxybenzylpindolol has similar affinities for β-1 and β-2-adrenergic receptors, it is possible to determine the total concentration of β-adrenergic receptors in a tissue by Scatchard analysis of specific (125I)-iodohydroxybenzylpindolol binding. In the presence of GTP, inhibition of specific (125I)-iodohydroxybenzylpindolol binding in rat heart, lung and five regions of rat brain by agonists and antagonists that are not specific for β-1 or β-2-adrenergic receptors yields linear Hofstee plots with Hill coefficients of approximately 1.0. On the other hand, the inhibition of specific (125I)-iodohydroxybenzylpindolol binding by drugs which have been shown to have different affinities for heart (β-1) and lung (β-2) receptors in vitro results in nonlinear Hofstee plots in each of these tissues. Two of these drugs (practolol and metoprolol) are more potent on β-1 than β-2 receptors and two of these drugs (zinterol and salmefamol) are more potent on β-2 than on β-1 receptors. The nonlinear Hofstee plots are consistent with there being two types of binding sites in each of the tissues with different affinities for the drugs. The relative number of each type of binding site and the affinity of each drug for each of the two types of site has been calculated using a computer based iterative procedure. Using this method, the relative percentages of the two receptor subtypes in rat heart, lung, cerebral cortex, caudate, cerebellum, hippocampus and diencephalon were determined. In each tissue, the use of four different drugs with different in vitro selectivity (two β-1 selective and two β-2 selective) resulted in approximately the same calculated β-1/β-2 ratio. This suggests that the assumption that the nonlinear Hofstee plots are composed of only two components is correct. In addition, the calculated affinity of each drug for β-1 and β-2 receptors was quantitatively similar in each of the seven tissues examined. The calculated ratios of β-l:β-2-adrenergic receptors are: heart 83:17; lung 15:85; cortex 81:19; caudate 76:24; cerebellum 15:85; hippocampus 81:19; and diencephalon 71:29. The absolute concentrations of β-1-adrenergic receptors in the brain regions examined varied by almost 20-fold. However, the absolute concentration of β-2-adrenergic receptors varied less than 3-fold. This suggests that β-2-adrenergic receptors in rat brain are associated with a more homogeneously distributed cellular element than are β-1-adrenergic receptors.