脾淋巴细胞α_2-肾上腺素能受体的特征和功能的实验研究

Studies on characteristics and function of alpha2-adrenoceptors intact lymphocytes isolated from rat spleen

用放射配基结合法研究大鼠脾淋巴细胞α_2-肾上腺素能受体的特征。~3H-可乐定(~3H-CLO)与脾淋巴细胞的结合呈现快速(t1/2:2min)、可逆(t1/2:3—4min)、高亲和力(K_D:6.57±SD1.63nM)、可饱和性(B_(?a):72.4±SD13.4fmo1/10~?细胞)(n=6)和立体结构特异性等特征,表明脾淋巴细胞存在α_2-肾上腺素能受体。肾上腺素能受体激动剂抑制~3H-CLO结合的效能顺序是:肾上腺素>去甲肾上腺素>异丙肾上腺素,表明为α_2亚型。竞争实验资料的计算机分析提示,脾淋巴细胞α_2-肾上腺素能受体存在高、中、低三种亲和力状态,彼此相差2～3个数量级。在体外诱生抗体中,10umo1.L^(-1)可乐定显著抑制诱生的IgM量,可被10umol:L^(-1)酚妥拉明阻断,表明脾淋巴细胞α_2肾上腺素能受体激活抑制抗体应答。

~3H-Clonidine, a potent and selective alpha2-adrenergic agonist was used to label alpha2-a-drenoceptors in intact lymphocytes isolated from rat spleen. Binding of ~3H-Clo-nidine was rapid(t1/2: 2min)and readily reversed by 10umol·L^(-1) clonidine(t1/2: 3-4min). ~3H-Clonidine saturationexperiments indicated a single c1ass of site with a K_D of 6.57±1.63nM and Bmax of 72.4±13.4 fmol/10~7 lymphocytes. Adrenergic agonists competed for ~3H-clonidine binding site with anorder of potency:epinephrine)norepinephrine)isoproterenol. These results show the presence ofalpha2-adrenoceptors in splenic lymphocytes. Computer analysis of competition experiments withadrenergic agonists revealed three classes of sites: high affinity site, medium affinity site and lowaffinity site. The affinity of high affinity site is 2-3 orders of magnitude higher than the one ofmedium affinity site, whereas the latter is the same orders higher than low affinity site Using im-proved Mishell-Dutton method, 10umol·L^(-1) clonidine suppressed the Ig M synthesis and thesuppression was blocked by 10 umol·L^(-1) phentolamine. These results indicate the suppression ofIg M antibody response to SRBC in vitro by clonidine is mediated by the alpha-adrenoceptors.