自然衰老大鼠脑线粒体和血小板膜外周型苯二氮 受体结合活性的变化

Change of Peripheral-type Benzodiazepine Receptors in Brain Mitochodria and Platelet Membrane in Aging Rat

目的以3月龄青年大鼠为对照,观察24月龄自然衰老大鼠大脑皮层线粒体和血小板膜外周型苯二氮受体(PBRs)结合数量及亲和力的改变。方法雄性SD大鼠断头取脑,以差速离心法提取大脑皮层线粒体,低渗溶血法制备外周血小板膜。采用放射配基[3H]PK11195单点结合实验测定PBRs特异结合活性,通过受体饱和实验和Scatchard作图得到最大结合容量Bmax值和平衡解离常数Kd值。结果与3月龄组大鼠相比,24月龄组的大脑皮层线粒体及外周血小板膜PBRs特异结合活性均显著上升(P<0.001)。饱和实验结果表明,24月龄组大鼠大脑皮层线粒体PBRs的受体容量(Bmax)升高而受体亲和力明显下降,Kd值显著增高(P<0.001)。结论老龄鼠PBRs容量上升而亲和力下降,可能参与脑老化进程。外周血小板膜[3H]PK11195结合活性与脑内该指标的变化一致。

Objective To evaluate the quantitative and qualitative changes of peripheral-type benzodiazepine recepors （PBRs） in brain mitochodria and in platelet membrane in aging rats. Methods Male Sprague-Dawley rats were divided into 3-and 24-month groups. All animals were sacrificed by decapitation and the brains were immediately removed. Mitochondrial components from dissected cerebral cortex were isolated. The membrane of platelets from venous blood was prepared by the method of hypotonic hemolysis. The specific binding assay of the radioactive PBRs antagonist [^3H]PK11195 to membrane was performed. Scatchard analysis was performed to estimate the equilibrium dissociation constant （Kd） and the maximal binding site density （Bmax）. Results A significant increase in [^3H]PK11195 binding activity in the mitochodria from cerebral cortex in 24-month rats was observed compared to that in 3-month rats（P〈0.001）. Meanwhile,the Scatchard analysis revealed that there was an increase in Bmax,with a significant increase in Kd in 24-month rats. The same change of [^3H]PK11195 binding activity was noted for platelet membrane in 24-month rats（P〈0.001）.Conclusion The density of PBRs increases in cortex mitochondria in aging rats,but the binding affinity of PBRs decreases which may be attributable to the progressive pathogenesis of aging in rats. [^3H] PK11195 binding activity of platelet membrane might reflect the change of PBRs in the brain tissue.