MECHANISMS OF B1 AND B2 ADRENERGIC ACTIONS IN CANINE HEART CELLS

β-肾上腺素能受体（β AR）介导的心肌细胞凋亡的调节 性能是心血管储备功能的主要组成部分。 虽然有几种不同类型的β AR，但在 心肌主要是β 1 AR。然而，现在强有力的证据表明， β 1AR和β 2AR亚型在各种心脏中共存， 哺乳动物物种，这两种aAR亚型的刺激发挥了重要作用。 在调节心脏功能中的重要作用。因为 老年人和老年人对β AR刺激的收缩反应降低， 心脏衰竭伴随着β 1 AR的大量丧失， β 2 AR的缺失，β 2 AR激活对改善 心脏性能受到了相当大的关注。最近我们 表明β 1 AR和β 2 AR在功能上共存， β 2AR刺激增加L型Ca 2 + 电流（伊卡）、胞质Ca 2+（Cai）瞬变和收缩。然而，在这方面， β 2 AR刺激对心脏Ca 2+代谢的作用， 收缩性在很大程度上与cAMP的产生无关， 大鼠心肌细胞中受磷蛋白磷酸化。百日咳毒素 (PTX)预处理特异性增强β 2 AR刺激的 增加Cai瞬变，收缩和伊卡。在本研究中， 发现虽然锌特罗刺激β 2 AR确实诱导了一种阳性反应， 正性肌力作用和增加伊卡和Cai瞬变，它没有影响 对细胞cAMP产生或受磷蛋白磷酸化的影响， 犬肌细胞这些结果有力地表明，cAMP信号传导 通路可能不参与犬心脏β 2 AR刺激。 此外，虽然β 1 AR激动剂诱导的伊卡增加， NE完全被一种特异性的肽抑制剂所阻断， cAMP依赖性蛋白激酶（PKI，50 μ M，在移液管填充溶液中）， β 2 AR刺激的锌特罗增加伊卡持续存在， 的PKI。此外，G蛋白抑制剂GDP β S（5 mM），包括在 移液管填充溶液完全消除了β 2 AR的作用， 以及β 1 AR刺激对伊卡的影响。综上所述，我们得出结论， 而β 1 AR刺激对伊卡的影响完全是由于 cAMP依赖性蛋白磷酸化，β 2 AR刺激的作用 对伊卡的影响可能是由非cAMP依赖性G蛋白偶联的 犬心室肌细胞中的信号通路。

The beta-adrenergic receptor (betaAR) mediated modulation of myocardial performance is a major component of cardiovascular reserve function. While there are several different types of betaAR, those in the myocardium are primarily beta1AR.However, now strong evidence suggests that both beta1AR and beta2AR subtypes coexist in the hearts of various mammalian species, and that stimulation of both aAR subtypes play a significant role in the regulation of cardiac performance. Because the reduced contractile response to betaAR stimulation in both aged and failing hearts is accompanied by a substantial loss of beta1AR, with no loss of beta2AR, the potential role of beta2AR activation for improving cardiac performance has received considerable attention. Recently, we demonstrated that both beta1AR and beta2AR functionally coexist in cardiac myocytes and that beta2AR stimulation augments L-type Ca2+ current (ICa), cytosolic Ca2+ (Cai) transient, and contraction. However, the actions of beta2AR stimulation on cardiac Ca2+ metabolism and contractility are largely dissociated from cAMP production and phospholamban phosphorylation in rat heart myocytes. Pertussis toxin (PTX) pretreatment specifically potentiates the beta2AR stimulated increases in Cai transient, contraction and ICa.In the present study,we found that while beta2AR stimulation by zinterol does induce an positive inotropic effect and increases in ICa and Cai transient, it has no effect on cellular cAMP production or on phospholamban phosphorylation in canine myocytes. These results strongly suggest that cAMP signalling pathway may not be involved in canine cardiac beta2AR stimulation. Furthermore, while the augmentation of ICa induced by beta1AR agonist, NE, is completely blocked by a specific peptide inhibitor of cAMP-dependent protein kinase (PKI, 50 muM in pipette filling solution), beta2AR stimulated increase in ICa by zinterol persists in the presence of PKI. In addition, a G protein inhibitor, GDPbetaS (5 mM), included in pipette filling solution completely abolished the actions of beta2AR as well as beta1AR stimulation on ICa. Taken together, we conclude that while the effect of beta1AR stimulation on ICa is due exclusively to cAMP-dependent protein phosphorylation, the effect of beta2AR stimulation on ICa may be mediated by non-cAMP-dependent G protein(s)-coupled signalling pathway(s) in canine ventricular myocytes.