Wahl C A, Trendelenburg A U, Starke K
Pharmakologisches Institut, Freiburg i.Br., Germany.
Naunyn Schmiedebergs Arch Pharmacol. 1996 Aug-Sep;354(3):253-61. doi: 10.1007/BF00171055.
Presynaptic alpha 2-autoreceptors in mouse atria were characterized in terms of the alpha 2A, alpha 2B, alpha 2C and alpha 2D subtypes. Segments of the atria were preincubated with 3H-noradrenaline and then superfused and stimulated electrically. The affinity of up to 16 antagonists for the autoreceptors was assessed as (1) pEC30% values. i.e. concentrations that increased previously autoinhibited release of 3H-noradrenaline (120 pulses, 3 Hz) by 30%, and (2) pKd values against the release-inhibiting effect of 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) under conditions of no or little autoinhibition (2 trains of 20 pulses, 50 Hz, train interval 120 s). The pKd values correlated well with the pEC30% values (r = 0.98; P < 0.001; slope of regression line 0.93), indicating that UK 14,304 and released noradrenaline modulated the release of noradrenaline through pharmacologically identical receptors. Comparison with antagonist affinities for (1) prototypic native alpha 2 radioligand binding sites, (2) radioligand binding sites in COS cells transfected with alpha 2 subtype genes, and (3) previously classified presynaptic alpha 2-autoreceptors-all taken from the literature-indicated that the mouse atrial autoreceptors corresponded to the alpha 2D subtype. For example, the pKd values at mouse atrial auto-receptors correlated closely with pKd values at native alpha 2D binding sites in the bovine pineal gland (r = 0.96; P < 0.001); with pKd values at alpha 2D binding sites in COS cells transfected with the rat alpha 2D gene (r = 0.85; P < 0.01); and with pKd values at guinea-pig cerebral and atrial and mouse cerebral alpha 2D-autoreceptors (r = 0.96-0.98; P < 0.001). The antagonist pKd values at mouse atrial autoreceptors correlated less with pKd values at alpha 2A, alpha 2B and alpha 2C sites. It is concluded that the presynaptic alpha 2-autoreceptors in mouse atria are alpha 2D. This identification supports the hypothesis that at least the majority of alpha 2-autoreceptors belong to the alpha 2A/D pair of orthologous alpha 2-adrenoceptors.
通过α2A、α2B、α2C和α2D亚型对小鼠心房中的突触前α2 - 自身受体进行了表征。将心房片段与3H - 去甲肾上腺素预孵育，然后进行灌流并电刺激。评估了多达16种拮抗剂对自身受体的亲和力，方法为：(1)pEC30%值，即能使先前自身抑制的3H - 去甲肾上腺素释放（120个脉冲，3Hz）增加30%的浓度；(2)在无自身抑制或自身抑制很小的条件下（2组，每组20个脉冲，50Hz，组间间隔120秒），针对5 - 溴 - 6 - (2 - 咪唑啉 - 2 - 基氨基) - 喹喔啉（UK 14,304）的释放抑制作用的pKd值。pKd值与pEC30%值相关性良好（r = 0.98；P < 0.001；回归线斜率为0.93），表明UK 14,304和释放的去甲肾上腺素通过药理学上相同的受体调节去甲肾上腺素的释放。与拮抗剂对(1)原型天然α2放射性配体结合位点、(2)转染了α2亚型基因的COS细胞中的放射性配体结合位点以及(3)先前分类的突触前α2 - 自身受体的亲和力进行比较（所有数据均来自文献），结果表明小鼠心房自身受体对应于α2D亚型。例如，小鼠心房自身受体的pKd值与牛松果体中天然α2D结合位点的pKd值密切相关（r = 0.96；P < 0.001）；与转染了大鼠α2D基因的COS细胞中α2D结合位点的pKd值相关（r = 0.85；P < 0.01）；与豚鼠脑和心房以及小鼠脑α2D - 自身受体的pKd值相关（r = 0.96 - 0.98；P < 0.001）。小鼠心房自身受体的拮抗剂pKd值与α2A、α2B和α2C位点的pKd值相关性较小。得出的结论是，小鼠心房中的突触前α2 - 自身受体为α2D。这一鉴定结果支持了以下假设，即至少大多数α2 - 自身受体属于α2 - 肾上腺素能受体的α2A/D直系同源对。
