β_3受体激动剂对培养的大鼠心肌细胞搏动频率和细胞内环一磷酸腺苷水平的影响

EFFECTS OF β_3-ADRENERGIC RECEPTORS AGONIST ON BEATING RATE AND cAMP LEVELS IN CULTURED CARDIOMYOCYTES OF RATS

目的 :观察 β3 受体激动剂 (BRL 37344 )对培养的大鼠心肌细胞搏动频率和细胞内环 -磷酸腺苷 (cAMP)水平的影响 ,以探讨 β3 受体在心肌细胞中的作用。方法 :分离培养乳鼠心肌细胞 ,随机分为八组 :对照组、ISO组、Nadolol+ISO组、BRL组、PTX +BRL组、L NAME +BRL、Nadolol+BRL组和Bupranolol+BRL组 ,观察心肌细胞搏动频率 ,并应用酶联免疫方法测定cAMP含量 ,逆转录多聚酶链反应 (RT PCR)方法测 β3 受体mRNA表达。结果 :ISO(非选择性 β受体激动剂 )可显著增加心肌细胞搏动频率和升高cAMP水平 ,这种作用可被Nadolol(为 β1,β2 受体抑制剂 )阻断。BRL 37344可显著降低心肌细胞搏动频率和cAMP含量 ,这种作用可被PTX(Gi 蛋白抑制剂 )和Bupranolol(非选择性 β受体阻滞剂 )完全阻断 ,同时可被L NAME(一氧化氮合酶抑制剂 )部分阻断 ,不受Nadolol影响。RT PCR方法测出心肌细胞中有 β3 受体mRNA表达。结论 :心肌细胞中存在 β3 受体 ,它在心肌表现为负性变力作用 ,β3 受体的效应不受 β1,β2 受体抑制剂影响。心脏 β3 受体信号途径中可能有Gi 蛋白的参与 ,并且经过一氧化氮合酶途径发挥其作用。

Aim: To evaluate the effects of β 3-adrenergic receptors (ARs) agonist(BRL-37344) on beating rate and cAMP levels and investigate the influence on the chronotropic action of β 3-ARs in cultured cardiomyocytes of rats. Methods: Cultured neonatal rat cardiomyocytes were divided randomly into eight groups, control group, ISO group, Nadolol+ISO group, BRL group, PTX+BRL group, L-NAME+ BRL group, Nadolol+ BRL group and Bupranolol+ BRL group. Beating rate of culture neonatal rat cardiomyocytes was observed and cAMP was measured by enzyme immunoassay kit. Expression levels of β 3- ARs mRNA in cardiomyocytes was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Results: ISO, nonspecific β-ARs agonist increased beating rate and intracellular cAMP production , antagonized by Nadolol, β 1 ,β 2-ARs antagonist. BRL37344 decreased beating rate and intracellular cAMP levels. PTX, Gi protein inhibitor and Bupranolol, nonspecific β-ARs antagonist totally blocked the effect and L-NAME, nitric oxide synthase (NOS) inhibitor partly blocked the effect, but Nadolol did not. There was the expression of β 3-AR mRNA in cardiomyocytes by RT-PCR. Conclusions: β 3-ARs showed in cardiomyocytes and produced negative chronotropic effects. β 1 ,β 2-ARs antagonist did not affect it. It suggested β 3-ARs signal transduction was related with G i protein. The negative inotropic effect of β 3-ARs stimulation was mediated by activation of the NOS pathway.