Chen Michael J, Zhu H E, Piletz John E
California State University, Los Angeles, California 90032, USA.
Ann N Y Acad Sci. 2003 Dec;1009:427-38. doi: 10.1196/annals.1304.057.
Imidazoline-1 receptors (I(1)R) and alpha(2)-noradrenergic receptors (alpha(2)AR) are known to coexist in many cell types and bind many of the same imidazoline ligands. Herein, the possibility of an interaction between these receptors was explored using a cloned cDNA that encodes a protein with I(1)R-like binding properties, designated imidazoline receptor antisera-selected (IRAS). Chinese hamster ovary (CHO) sublines permanently expressing the human subtype alpha(2A)AR cDNA were transiently cotransfected with the human IRAS cDNA (pIRAS). Saturation radioligand binding experiments on membranes isolated from the various sublines allowed distinction between I(1)R and alpha(2A)AR. Transfection of pIRAS into either subline led to a rise in membrane I(1)R-binding sites. Immunoblotting revealed that IRAS was enriched in membranes more than in cytosolic fractions. Transfection of pIRAS in CHO cells harboring the alpha(2A)AR cDNA resulted in a twofold increase in alpha(2A)AR binding sites with no change in alpha(2A)AR binding affinity, compared with controls. Immunoblotting also revealed increased expression of membranous alpha(2A)AR by IRAS. Thus, pIRAS transfection led to I(1) binding sites and to an increase in alpha(2A)AR binding sites in CHO cells expressing the human alpha(2A)AR. Although the mechanism is unclear, this increase in binding sites may explain previous imidazoline drug effects suggestive of interactions between these two receptors.
已知咪唑啉 -1 受体（I(1)R）和α(2)-去甲肾上腺素能受体（α(2)AR）在许多细胞类型中共存，并结合许多相同的咪唑啉配体。在此，使用一种克隆的 cDNA 探索了这些受体之间相互作用的可能性，该 cDNA 编码一种具有 I(1)R 样结合特性的蛋白质，命名为咪唑啉受体抗血清选择蛋白（IRAS）。将永久表达人α(2A)AR cDNA 的中国仓鼠卵巢（CHO）亚系与人类 IRAS cDNA（pIRAS）进行瞬时共转染。对从各种亚系中分离出的膜进行饱和放射性配体结合实验，可区分 I(1)R 和α(2A)AR。将 pIRAS 转染到任一亚系中都会导致膜 I(1)R 结合位点增加。免疫印迹显示，IRAS 在膜中的富集程度高于胞质部分。与对照相比，将 pIRAS 转染到携带α(2A)AR cDNA 的 CHO 细胞中，导致α(2A)AR 结合位点增加了两倍，而α(2A)AR 结合亲和力没有变化。免疫印迹还显示 IRAS 使膜性α(2A)AR 的表达增加。因此，pIRAS 转染导致表达人α(2A)AR 的 CHO 细胞中出现 I(1)结合位点，并使α(2A)AR 结合位点增加。尽管其机制尚不清楚，但结合位点的这种增加可能解释了先前咪唑啉药物效应所暗示的这两种受体之间的相互作用。
