Dash D, Rao K
Department of Biochemistry, Banaras Hindu University, Varanasi, India.
Biochem J. 1995 Jul 1;309 ( Pt 1)(Pt 1):99-104. doi: 10.1042/bj3090099.
Propranolol inhibits platelet secondary aggregation and secretion by mechanisms unrelated to its beta-adrenergic-blocking activity. We previously reported that a major effect of the drug is perturbation of the physical microenvironment of the human platelet membrane. To explore further the molecular mechanisms underlying propranolol-mediated platelet inhibition, we studied protein kinase C activity, estimated from the phosphorylation of the substrate protein pleckstrin, in propranolol-treated human platelets. The drug inhibited activation of the enzyme in thrombin-stimulated platelets but not in platelets stimulated with phorbol esters, indicating that its site of action might be upstream of protein kinase C. It also inhibited the activity of phospholipase C, determined from the extent of generation of inositol phosphates and phosphatidic acid, in platelets stimulated with thrombin as well as the non-hydrolysable GTP analogue guanosine 5'-[beta, gamma-imido]triphosphate in a dose-dependent manner. These data suggest that propranolol inhibits signal transduction in thrombin-stimulated platelets by interacting at the level of phospholipase C and exclude interaction of the drug with the downstream effector enzyme protein kinase C.
普萘洛尔通过与其β-肾上腺素能阻断活性无关的机制抑制血小板的二次聚集和分泌。我们之前报道过，该药物的主要作用是扰乱人血小板膜的物理微环境。为了进一步探究普萘洛尔介导的血小板抑制作用的分子机制，我们研究了用普萘洛尔处理的人血小板中蛋白激酶C的活性，该活性通过底物蛋白普列克底物蛋白的磷酸化来估算。该药物抑制凝血酶刺激的血小板中该酶的活化，但不抑制佛波酯刺激的血小板中的活化，这表明其作用位点可能在蛋白激酶C的上游。它还以剂量依赖的方式抑制凝血酶刺激的血小板中磷脂酶C的活性（根据肌醇磷酸和磷脂酸的生成程度来测定）以及不可水解的GTP类似物鸟苷5'-[β,γ-亚氨基]三磷酸的活性。这些数据表明，普萘洛尔通过在磷脂酶C水平上相互作用来抑制凝血酶刺激的血小板中的信号转导，并且排除了该药物与下游效应酶蛋白激酶C的相互作用。
