Hillman Kristin L, Doze Van A, Porter James E
Department of Pharmacology, Physiology, and Therapeutics, University of North Dakota School of Medicine and Health Sciences, 501 North Columbia Road, Stop 9037, Grand Forks, North Dakota 58202-9037, USA.
J Pharmacol Exp Ther. 2007 Jun;321(3):1062-8. doi: 10.1124/jpet.106.119297. Epub 2007 Mar 2.
The importance of adrenergic receptors (ARs) in the hippocampus has generally focused on betaARs; however, interest is growing in hippocampal alphaARs given their purported neuroprotective role. We have previously reported alpha(1)AR transcripts in a subpopulation of cornu ammonis 1 (CA1) interneurons. The goal of this study was to identify the specific alpha(1)AR subtype (alpha(1A), alpha(1B), alpha(1D)) functionally expressed by these cells. Using cell-attached recordings to measure action potential frequency changes, concentration-response curves for the selective alpha(1)AR agonist phenylephrine (PE) were generated in the presence of competitive subtype-selective alpha(1)AR antagonists. Schild regression analysis was then used to estimate equilibrium dissociation constants (K(b)) for each receptor antagonist in our system. The selective alpha(1A)AR antagonists, 5-methylurapidil and WB-4101 [2-[(2,6-dimethoxyphenoxyethyl)aminomethyl]-1,4-benzodioxane hydrochloride], produced consecutive rightward shifts in the concentration-response curve for PE when used at discriminating, nanomolar concentrations. Calculated K(b) values for 5-methylurapidil (10 nM) and WB-4101 (5 nM) correlate to previously published affinity values for these antagonists at the alpha(1A)AR. The selective alpha(1B)AR antagonist L-765,314 [(2S)-4-(4-amino-6,7-dimethoxy-2-quinazolinyl)-2-[[(1,1-dimethylethyl)amino]carbonyl]-1-piperazinecarboxylic acid], as well as the selective alpha(1D)AR antagonist BMY7378 [8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride], produced significant rightward shifts in the concentration-response curve for PE only when used at nondistinguishing, micromolar concentrations. Calculated K(b) values for L-765,314 (794 nM) and BMY7378 (316 nM) do not agree with affinity values for these antagonists at the alpha(1B) or alpha(1D)AR, respectively. Rather, these K(b) values more closely match equilibrium dissociation constants estimated for these compounds when used to identify alpha(1A)AR subtypes. Together, our results provide strong evidence to support functional expression of alpha(1A)ARs in a subpopulation of CA1 interneurons.
海马体中肾上腺素能受体（ARs）的重要性一般集中在β肾上腺素能受体；然而，鉴于海马体α肾上腺素能受体据称具有神经保护作用，人们对其的兴趣与日俱增。我们之前报道过在海马角1（CA1）中间神经元的一个亚群中存在α(1)AR转录本。本研究的目的是确定这些细胞功能性表达的特定α(1)AR亚型（α(1A)、α(1B)、α(1D)）。利用细胞贴附记录来测量动作电位频率变化，在竞争性亚型选择性α(1)AR拮抗剂存在的情况下，生成了选择性α(1)AR激动剂去氧肾上腺素（PE）的浓度-反应曲线。然后使用希尔回归分析来估计我们系统中每种受体拮抗剂的平衡解离常数（K(b)）。当以区分性的纳摩尔浓度使用时，选择性α(1A)AR拮抗剂5-甲基乌拉地尔和WB-4101 [2-[(2,6-二甲氧基苯氧基乙基)氨基甲基]-1,4-苯并二恶烷盐酸盐]使PE的浓度-反应曲线连续向右移动。5-甲基乌拉地尔（10 nM）和WB-4101（5 nM）的计算K(b)值与这些拮抗剂在α(1A)AR上先前公布的亲和力值相关。选择性α(1B)AR拮抗剂L-765,314 [(2S)-4-(4-氨基-6,7-二甲氧基-2-喹唑啉基)-2-[[(1,1-二甲基乙基)氨基]羰基]-1-哌嗪羧酸]以及选择性α(1D)AR拮抗剂BMY7378 [8-[2-[4-(2-甲氧基苯基)-1-哌嗪基]乙基]-8-氮杂螺[4.5]癸烷-7,9-二酮二盐酸盐]，仅在以非区分性的微摩尔浓度使用时，才使PE的浓度-反应曲线显著向右移动。L-765,314（794 nM）和BMY7378（316 nM）的计算K(b)值分别与这些拮抗剂在α(1B)或α(1D)AR上的亲和力值不一致。相反，这些K(b)值与这些化合物用于鉴定α(1A)AR亚型时估计的平衡解离常数更接近。总之，我们的结果提供了有力证据，支持α(1A)ARs在CA1中间神经元亚群中的功能性表达。
