Overexpression of beta 1 and beta 2 adrenergic receptors in rat atrial myocytes. Differential coupling to G protein-gated inward rectifier K(+) channels via G(s) and G(i)/o.
Overexpression of beta 1 and beta 2 adrenergic receptors in rat atrial myocytes. Differential coupling to G protein-gated inward rectifier K(+) channels via G(s) and G(i)/o.
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DOI：
10.1074/jbc.m106234200
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发表时间：
2001-10
期刊：
影响因子：
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通讯作者：
M. Wellner-Kienitz;K. Bender;L. Pott
中科院分区：
文献类型：
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作者：
M. Wellner-Kienitz;K. Bender;L. Pott
G蛋白激活的内向纠偏K(+) （GIRK）通道在心房肌细胞、各种神经元和内分泌细胞中表达，代表了活化的异三聚体G蛋白释放的β - γ亚基的典型靶标。这些通道有助于心脏频率的生理减慢和突触抑制。它们被与百日咳毒素敏感的G蛋白（G(i/o)）偶联的受体刺激后释放的β - γ二聚体激活，而从G(s)释放的β - γ不会聚集在通道亚基上。这与各种β和γ亚基的二聚体组合可以以很少的特异性激活GIRK通道的发现相冲突。在本研究中，我们通过瞬时转染在心房肌细胞中过度表达了心脏β -肾上腺素能受体的主要亚型(β （1)-AR和β (2)-AR）。而在天然细胞中，异丙肾上腺素的β -肾上腺素能刺激不能诱导可测量的GIRK电流，从过度表达β (1)-AR或β (2)-AR的肌细胞中记录到强劲的电流。β (2)- ar诱导的电流对百日咳毒素的敏感性与内源性G（i/o）偶联毒蕈碱M(2)受体引起的电流相同，而异丙肾上腺素激活的电流在β (1)- ar过表达的肌细胞中对百日咳毒素不敏感。与最近发表的一篇文章(Leaney， J. L., Milligan， G., and Tinker, a .（2000）相比，J. Biol.；化学，275,921-929)，当瞬时转染两种不同的标准细胞系（中国仓鼠卵巢和HEK293）重建信号通路时，异丙肾上腺素也可以激活相当大的GIRK电流。这些结果表明受体- g蛋白信号的特异性可以被受体的过表达破坏。此外，异三聚体G蛋白的α亚基对G β γ介导的信号传导没有特异性。
G protein-activated inwardly rectifying K(+) (GIRK) channels, expressed in atrial myocytes, various neurons, and endocrine cells, represent the paradigmatic target of beta gamma subunits released from activated heterotrimeric G proteins. These channels contribute to physiological slowing of cardiac frequency and synaptic inhibition. They are activated by beta gamma dimers released upon stimulation of receptors coupled to pertussis toxin-sensitive G proteins (G(i/o)), whereas beta gamma released from G(s) do not converge on the channel subunits. This is in conflict with the finding that dimeric combinations of various beta and gamma subunits can activate GIRK channels with little specificity. In the present study, we have overexpressed the major subtypes of cardiac beta-adrenergic receptors (beta(1)-AR and beta(2)-AR) in atrial myocytes by transient transfection. Whereas in native cells beta-adrenergic stimulation with isoproterenol failed to induce measurable GIRK current, robust currents were recorded from myocytes overexpressing either beta(1)-AR or beta(2)-AR. Whereas the beta(2)-AR-induced current showed the same sensitivity to pertussis toxin as the current evoked by the endogenous G(i/o)-coupled muscarinic M(2) receptor, isoproterenol-activated currents were insensitive to pertussis toxin treatment in beta(1)-AR-overexpressing myocytes. In contrast to a recent publication (Leaney, J. L., Milligan, G., and Tinker, A. (2000) J. Biol. Chem. 275, 921-929), sizable GIRK currents could also be activated by isoproterenol when the signaling pathway was reconstituted by transient transfection in two different standard cell lines (Chinese hamster ovary and HEK293). These results demonstrate that specificity of receptor-G protein signaling can be disrupted by overexpression of receptors. Moreover, the alpha subunit of heterotrimeric G proteins does not confer specificity to G beta gamma-mediated signaling.