González-Rodríguez P, Falcón D, Castro M J, Ureña J, López-Barneo J, Castellano A
Instituto de Biomedicina de Sevilla (IBiS), Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, Sevilla, Spain.
Departamento de Fisiología Médica y Biofísica, Facultad de Medicina, Universidad de Sevilla, Sevilla, Spain.
J Physiol. 2015 Nov 1;593(21):4729-45. doi: 10.1113/JP271053. Epub 2015 Oct 1.
T-type Ca(2+) channels are expressed in the ventricular myocytes of the fetal and perinatal heart, but are normally downregulated as development progresses. Interestingly, however, these channels are re-expressed in adult cardiomyocytes under pathological conditions. We investigated low voltage-activated T-type Ca(2+) channel regulation in hypoxia in rat cardiomyocytes. Molecular studies revealed that hypoxia induces the upregulation of Cav 3.2 mRNA, whereas Cav 3.1 mRNA is not significantly altered. The effect of hypoxia on Cav 3.2 mRNA was time- and dose-dependent, and required hypoxia inducible factor-1α (HIF-1α) stabilization. Patch-clamp recordings confirmed that T-type Ca(2+) channel currents were upregulated in hypoxic conditions, and the addition of 50 μm NiCl2 (a T-type channel blocker) demonstrated that the Cav 3.2 channel is responsible for this upregulation. This increase in current density was not accompanied by significant changes in the Cav 3.2 channel electrophysiological properties. The small monomeric G-protein RhoA and its effector Rho-associated kinase I (ROCKI), which are known to play important roles in cardiovascular physiology, were also upregulated in neonatal rat ventricular myocytes subjected to hypoxia. Pharmacological experiments indicated that both proteins were involved in the observed upregulation of the Cav 3.2 channel and the stabilization of HIF-1α that occurred in response to hypoxia. These results suggest a possible role for Cav 3.2 channels in the increased probability of developing arrhythmias observed in ischaemic situations, and in the pathogenesis of diseases associated with hypoxic Ca(2+) overload.
T型Ca(2+)通道在胎儿和围产期心脏的心室肌细胞中表达，但通常会随着发育进程而下调。然而，有趣的是，这些通道在病理条件下会在成年心肌细胞中重新表达。我们研究了大鼠心肌细胞缺氧时低电压激活的T型Ca(2+)通道调节。分子研究表明，缺氧诱导Cav 3.2 mRNA上调，而Cav 3.1 mRNA无明显变化。缺氧对Cav 3.2 mRNA的影响具有时间和剂量依赖性，且需要缺氧诱导因子-1α（HIF-1α）稳定化。膜片钳记录证实，缺氧条件下T型Ca(2+)通道电流上调，添加50μm NiCl2（一种T型通道阻滞剂）表明Cav 3.2通道负责这种上调。电流密度的增加并未伴随Cav 3.2通道电生理特性的显著变化。已知在心血管生理学中起重要作用的小单体G蛋白RhoA及其效应器Rho相关激酶I（ROCKI）在缺氧的新生大鼠心室肌细胞中也上调。药理学实验表明，这两种蛋白都参与了缺氧时观察到的Cav 3.2通道上调和HIF-1α稳定化。这些结果表明，Cav 3.2通道可能在缺血情况下观察到的心律失常发生概率增加以及与缺氧性Ca(2+)过载相关疾病的发病机制中发挥作用。
