Smani T, Hernández A, Ureña J, Castellano A G, Franco-Obregón A, Ordoñez A, López-Barneo J
Laboratorio de Investigaciones Biomédicas, Edificio de Laboratorios, 2 planta, Hospital Universitario Virgen del Rocío, Universidad de Sevilla, Avenida Manuel Siurot s/n, E-41013 Seville, Spain.
Cardiovasc Res. 2002 Jan;53(1):97-104. doi: 10.1016/s0008-6363(01)00422-9.
Oxygen (O(2)) tension is a major regulator of blood flow in the coronary circulation. Hypoxia can produce vasodilation through activation of ATP regulated K(+) (K(ATP)) channels in the myocyte membrane, which leads to hyperpolarization and closure of voltage-gated Ca(2+) channels. However, there are other O(2)-sensitive mechanisms intrinsic to the vascular smooth muscle since hypoxia can relax vessels precontracted with high extracellular K(+), a condition that prevents hyperpolarization following opening of K(+) channels. The objective of the present study was to determine whether inhibition of Ca(2+) influx through voltage-dependent channels participates in the response of coronary myocytes to hypoxia.
Experiments were performed on porcine anterior descendent coronary arterial rings and on enzymatically dispersed human and porcine myocytes of the same artery. Cytosolic [Ca(2+)] was measured by microfluorimetry and whole-cell currents were recorded with the patch clamp technique.
Hypoxia (O(2) tension approximately 20 mmHg) dilated endothelium-denuded porcine coronary arterial rings precontracted with high K(+) in the presence of glibenclamide (5 microM), a blocker of K(ATP) channels. In dispersed human and porcine myocytes, low O(2) tension decreased basal cytosolic [Ca(2+)] and transmembrane Ca(2+) influx independently of K(+) channel activation. In patch clamped cells, hypoxia reversibly inhibited L-type Ca(2+) channels. RT-PCR indicated that rHT is the predominant mRNA variant of the alpha(1C) Ca(2+) channel subunit in human coronary myocytes.
Our study demonstrates, for the first time in a human preparation, that voltage-gated Ca(2+)channels in coronary myocytes are under control of O(2) tension.
氧分压是冠状动脉循环中血流的主要调节因素。缺氧可通过激活心肌细胞膜上的ATP敏感性钾通道（KATP通道）产生血管舒张，这会导致超极化以及电压门控钙通道关闭。然而，血管平滑肌还存在其他对氧敏感的机制，因为缺氧可使预先用高细胞外钾预收缩的血管舒张，这种情况下钾通道开放后可阻止超极化。本研究的目的是确定抑制通过电压依赖性通道的钙内流是否参与冠状动脉心肌细胞对缺氧的反应。
对猪冠状动脉前降支动脉环以及对来自同一动脉的经酶分散的人及猪心肌细胞进行实验。通过微量荧光测定法测量胞浆内钙离子浓度，并采用膜片钳技术记录全细胞电流。
在存在格列本脲（5微摩尔）（一种KATP通道阻滞剂）的情况下，缺氧（氧分压约20毫米汞柱）可使预先用高钾预收缩的去内皮猪冠状动脉环舒张。在分散的人及猪心肌细胞中，低氧分压可独立于钾通道激活降低基础胞浆内钙离子浓度及跨膜钙内流。在膜片钳记录的细胞中，缺氧可可逆性抑制L型钙通道。逆转录聚合酶链反应表明，rHT是人冠状动脉心肌细胞中α1C钙通道亚基的主要信使核糖核酸变体。
我们的研究首次在人体标本中证明，冠状动脉心肌细胞中的电压门控钙通道受氧分压的调控。
