Studies on characteristics and function of alpha2-adrenoceptors intact lymphocytes isolated from rat spleen / 中国免疫学杂志

ABSTRACT

~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 potencyepinephrine)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.