Department of Pharmacology and Therapeutics, Faculty of Medicine, Universidad Autónoma de Madrid, Madrid, Spain.
J Neurochem. 2011 Jan;116(1):105-21. doi: 10.1111/j.1471-4159.2010.07089.x. Epub 2010 Dec 2.
This study examines the Cav1 isoforms expressed in mouse chromaffin cells and compares their biophysical properties and roles played in cell excitability and exocytosis. Using immunocytochemical and electrophysiological techniques in mice lacking the Cav1.3α1 subunit (Cav1.3(-/-) ) or the high sensitivity of Cav1.2α1 subunits to dihydropyridines, Cav1.2 and Cav1.3 channels were identified as the only Cav1 channel subtypes expressed in mouse chromaffin cells. Cav1.3 channels were activated at more negative membrane potentials and inactivated more slowly than Cav1.2 channels. Cav1 channels, mainly Cav1.2, control cell excitability by functional coupling to BK channels, revealed by nifedipine blockade of BK channels in wild type (WT) and Cav1.3(-/-) cells (53% and 35%, respectively), and by the identical change in the shape of the spontaneous action potentials elicited by the dihydropyridine in both strains of mice. Cav1.2 channels also play a major role in spontaneous action potential firing, supported by the following evidence: (i) a similar percentage of WT and Cav1.3(-/-) cells fired spontaneous action potentials; (ii) firing frequency did not vary between WT and Cav1.3(-/-) cells; (iii) mostly Cav1.2 channels contributed to the inward current preceding the action potential threshold; and (iv) in the presence of tetrodotoxin, WT or Cav1.3(-/-) cells exhibited spontaneous oscillatory activity, which was fully abolished by nifedipine perfusion. Finally, Cav1.2 and Cav1.3 channels were essential for controlling the exocytotic process at potentials above and below -10 mV, respectively. Our data reveal the key yet differential roles of Cav1.2 and Cav1.3 channels in mediating action potential firing and exocytotic events in the neuroendocrine chromaffin cell.
本研究探讨了在小鼠嗜铬细胞中表达的 Cav1 同工型，并比较了它们在细胞兴奋性和胞吐作用中发挥的生物物理特性和作用。使用免疫细胞化学和电生理技术在缺乏 Cav1.3α1 亚基（Cav1.3(-/-)）或 Cav1.2α1 亚基对二氢吡啶高敏感性的小鼠中，鉴定 Cav1.2 和 Cav1.3 通道为仅在小鼠嗜铬细胞中表达的 Cav1 通道亚型。Cav1.3 通道在更负的膜电位下被激活，并且失活比 Cav1.2 通道更慢。Cav1 通道，主要是 Cav1.2，通过与 BK 通道的功能偶联来控制细胞兴奋性，这通过硝苯地平阻断 WT 和 Cav1.3(-/-) 细胞中的 BK 通道（分别为 53%和 35%），以及在两种小鼠品系中由二氢吡啶引起的自发动作电位形状的相同变化得到证实。Cav1.2 通道在自发性动作电位发射中也起主要作用，这得到以下证据的支持：（i）WT 和 Cav1.3(-/-)细胞中自发性动作电位发射的百分比相似；（ii）WT 和 Cav1.3(-/-)细胞之间的发射频率没有变化；（iii）主要是 Cav1.2 通道有助于在动作电位阈值之前的内向电流；（iv）在存在河豚毒素的情况下，WT 或 Cav1.3(-/-)细胞表现出自发的振荡活性，该活性被硝苯地平灌注完全消除。最后，Cav1.2 和 Cav1.3 通道分别是控制电位在-10 mV 以上和以下的胞吐过程的必要条件。我们的数据揭示了 Cav1.2 和 Cav1.3 通道在介导神经内分泌嗜铬细胞中的动作电位发射和胞吐事件中的关键但不同的作用。
