Han H M, Robinson R B, Bilezikian J P, Steinberg S F
Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York.
Circ Res. 1989 Dec;65(6):1763-73. doi: 10.1161/01.res.65.6.1763.
During development, the cardiac alpha 1-adrenergic chronotropic response changes from positive in the neonate to negative in the adult. The negative chronotropic effect of alpha 1-adrenergic stimulation in the adult depends on maturation of sympathetic innervation and the presence of a pertussis toxin (PT)-sensitive guanine nucleotide-binding (G) protein. To examine the possibility of a developmental change in coupling of a PT-sensitive G protein to the alpha 1-adrenergic receptor, radioligand binding experiments with the iodinated alpha 1-selective radioligand [125I]-I-2-[beta-(4-hydroxyphenyl)ethylaminomethyl]tetralone ([ 125I]-IBE 2254) were performed on membranes prepared from control and PT-treated neonatal and adult rat hearts. Scatchard analysis showed fewer alpha 1-adrenergic receptors in the adult than in the neonate (168 +/- 10 fmol/mg protein in the neonate vs. 124 +/- 13 fmol/mg protein in the adult), but similar affinities (equilibrium dissociation constant 124 +/- 29 pM in the neonate vs. 140 +/- 34 pM in the adult). PT treatment did not alter the results. In both the neonate and adult, 5'-guanylylimidodiphosphate [Gpp(NH)p, 500 microM] shifted the l-epinephrine competition curve to the right and increased the slope factor toward unity. PT had no effect on the l-epinephrine competition curve in the neonate. However, in the adult PT itself caused a partial shift in the agonist competition curve, reducing but not eliminating the effect of Gpp(NH)p. Consistent with the results from the binding experiments, PT did not have any effect on the alpha 1-adrenergic-mediated positive chronotropic response in the neonate, whereas in the adult the alpha 1-adrenergic-mediated negative chronotropic response was completely converted to a positive one after PT treatment. These results indicate the presence of a PT-insensitive G protein in the neonatal and adult rat heart and the acquisition of a PT-sensitive G protein linked to the negative chronotropic response during development.
在发育过程中，心脏α1-肾上腺素能变时反应从新生儿期的阳性转变为成年期的阴性。α1-肾上腺素能刺激在成年期的负性变时作用取决于交感神经支配的成熟以及百日咳毒素（PT）敏感的鸟嘌呤核苷酸结合（G）蛋白的存在。为了研究PT敏感的G蛋白与α1-肾上腺素能受体偶联的发育变化可能性，使用碘化α1选择性放射性配体[125I]-I-2-[β-(4-羟基苯基)乙氨基甲基]四氢萘酮（[125I]-IBE 2254）对来自对照和PT处理的新生和成年大鼠心脏制备的膜进行放射性配体结合实验。Scatchard分析显示，成年大鼠心脏中的α1-肾上腺素能受体比新生大鼠心脏中的少（新生大鼠为168±10 fmol/mg蛋白，成年大鼠为124±13 fmol/mg蛋白），但亲和力相似（新生大鼠的平衡解离常数为124±29 pM，成年大鼠为140±34 pM）。PT处理未改变结果。在新生大鼠和成年大鼠中，5'-鸟苷酰亚胺二磷酸[Gpp(NH)p，500 μM]使l-肾上腺素竞争曲线右移，并使斜率因子增加至1。PT对新生大鼠的l-肾上腺素竞争曲线无影响。然而，在成年大鼠中，PT本身导致激动剂竞争曲线部分右移，降低但未消除Gpp(NH)p的作用。与结合实验结果一致，PT对新生大鼠心脏中α1-肾上腺素能介导的正性变时反应没有任何影响，而在成年大鼠中，PT处理后α1-肾上腺素能介导的负性变时反应完全转变为正性变时反应。这些结果表明，新生和成年大鼠心脏中存在PT不敏感的G蛋白，并且在发育过程中获得了与负性变时反应相关的PT敏感的G蛋白。
