Murray T F, Siebenaller J F
J Comp Physiol B. 1987;157(3):267-77. doi: 10.1007/BF00693353.
The binding properties of A1 adenosine receptors in brain membranes were compared in two congeneric marine teleost fishes which differ in their depths of distribution. Adenosine receptors were labeled using the A1 selective radioligand [3H]cyclohexyladenosine ([3H]CHA). The A1 receptor agonist [3H]CHA bound saturably, reversibly and with high affinity to brain membranes prepared from Sebastolobus altivelis and S. alascanus; however, the mean Kd values differed significantly (Figs. 1-3, Table 1). Saturation data fit to a one site model indicated that the A1 receptor in S. alascanus exhibited a higher affinity (Kd = 1.49 nM) for [3H]CHA whereas A1 receptors in S. altivelis exhibited a significantly lower affinity (Kd = 3.1 nM). Moreover, S. altivelis, but not S. alascanus, parameter estimates for [3H]CHA binding to two sites of receptor were obtained (Fig. 3, Table 1). The mean dissociation constant values for the high and low affinity sites for [3H]CHA in S. altivelis were 0.43 nM and 16.3 nM, respectively. In equilibrium competition experiments the adenosine analogs R-phenylisopropyladenosine (R-PIA), N-ethylcarboxamidoadenosine (NECA) and S-phenylisopropyladenosine (S-PIA) all displayed higher affinities for A1 receptors in S. alascanus as compared to S. altivelis brain membranes (Table 2, Fig. 6). The specific binding of [3H]CHA was significantly increased by 0.1 and 1.0 mM MgCl2 in both fishes; however, the sensitivity (95-131% increase) of S. altivelis to this effect was significantly greater than that of S. alascanus (48-91% increase) (Fig. 5). The results of kinetic, equilibrium saturation and equilibrium competition experiments all suggest that A1 adenosine receptors of S. altivelis and S. alascanus brain membranes differ with respect to their affinities for selected adenosine agonists.
在两种分布深度不同的同属海洋硬骨鱼类中，比较了它们脑膜中A1腺苷受体的结合特性。使用A1选择性放射性配体[3H]环己基腺苷（[3H]CHA）标记腺苷受体。A1受体激动剂[3H]CHA可饱和、可逆且高亲和力地结合于由高背岩鳕和阿拉斯加岩鳕制备的脑膜；然而，平均解离常数（Kd）值存在显著差异（图1 - 3，表1）。拟合到单一位点模型的饱和数据表明，阿拉斯加岩鳕中的A1受体对[3H]CHA表现出更高的亲和力（Kd = 1.49 nM），而高背岩鳕中的A1受体亲和力则显著较低（Kd = 3.1 nM）。此外，获得了高背岩鳕（而非阿拉斯加岩鳕）中[3H]CHA与受体两个位点结合的参数估计值（图3，表1）。高背岩鳕中[3H]CHA高亲和力和低亲和力位点的平均解离常数分别为0.43 nM和16.3 nM。在平衡竞争实验中，与高背岩鳕脑膜相比，腺苷类似物R - 苯异丙基腺苷（R - PIA）、N - 乙基羧基酰胺腺苷（NECA）和S - 苯异丙基腺苷（S - PIA）对阿拉斯加岩鳕中的A1受体均表现出更高的亲和力（表2，图6）。两种鱼中，0.1 mM和1.0 mM的MgCl2均显著增加了[3H]CHA的特异性结合；然而，高背岩鳕对这种效应的敏感性（增加95 - 131%）显著高于阿拉斯加岩鳕（增加48 - 91%）（图5）。动力学、平衡饱和和平衡竞争实验结果均表明，高背岩鳕和阿拉斯加岩鳕脑膜中的A1腺苷受体对所选腺苷激动剂的亲和力不同。
