Takimoto K, Li D, Nerbonne J M, Levitan E S
Department of Pharmacology, University of Pittsburgh, PA, 15261, USA.
J Mol Cell Cardiol. 1997 Nov;29(11):3035-42. doi: 10.1006/jmcc.1997.0532.
Dihydropyridine-sensitive voltage-gated (l-type) Ca2+ channels play an essential role in cardiac and smooth muscle excitation-contraction coupling. Transcripts for the two pore-forming subunits of l-type Ca2+ channels, alpha 1C and alpha 1D have been detected in heart and lung; however, distribution, structure and regulated expression of these channel subunit mRNAs have not been examined in detail. Here we use RNase protection and RT-PCR assays to identify cardiac-specific features of expression of the two channel mRNAs. First, expression of alpha 1D mRNA is found in lung, aorta and atrium, but is not detected in ventricle. Limited expression of alpha 1D mRNA is also seen in enriched preparations of cardiac myocytes: it is significant in atrial myocytes, but not in ventricular myocytes. Second, RT-PCR analyses indicate that atrial alpha 1D channels exclusively contains the 15-amino acid insertion between third and fourth segments in repeat IV. Finally, expression of alpha 1C mRNA, but not alpha 1D mRNA, is up-regulated by glucocorticoids in atrium and ventricle: adrenalectomy and subsequent injection of the glucocorticoid agonist dexamethasone decreased and increased the channel message, respectively. Dexamethasone also significantly increased the number of dihydropyridine-binding sites in ventricle. In contrast, alpha 1C mRNA levels were glucocorticoid-insensitive in lung and aorta. Thus, basal and glucocorticoid-induced expression, and splicing of the two l-type Ca2+ channel alpha 1 subunit transcripts are tissue specifically controlled in atria and ventricles of rat heart.
二氢吡啶敏感性电压门控（L型）Ca2+通道在心肌和平滑肌的兴奋-收缩偶联中起重要作用。在心脏和肺中已检测到L型Ca2+通道两个孔形成亚基α1C和α1D的转录本；然而，这些通道亚基mRNA的分布、结构和调控表达尚未得到详细研究。在此，我们使用核糖核酸酶保护和逆转录-聚合酶链反应（RT-PCR）分析来鉴定这两种通道mRNA表达的心脏特异性特征。首先，α1D mRNA在肺、主动脉和心房中表达，但在心室中未检测到。在富集的心肌细胞制剂中也可见α1D mRNA的有限表达：在心房肌细胞中显著，但在心室肌细胞中不显著。其次，RT-PCR分析表明，心房α1D通道在重复序列IV的第三和第四片段之间仅包含15个氨基酸的插入。最后，α1C mRNA而非α1D mRNA的表达在心房和心室中受糖皮质激素上调：肾上腺切除术后随后注射糖皮质激素激动剂地塞米松分别降低和增加了通道信息。地塞米松还显著增加了心室中二氢吡啶结合位点的数量。相比之下，α1C mRNA水平在肺和主动脉中对糖皮质激素不敏感。因此，大鼠心脏心房和心室中两种L型Ca2+通道α1亚基转录本的基础表达和糖皮质激素诱导表达以及剪接受组织特异性控制。
