Wang Hong-Sheng, Cohen Ira S
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA.
J Physiol. 2003 Mar 15;547(Pt 3):825-33. doi: 10.1113/jphysiol.2002.035410. Epub 2003 Jan 31.
Regional variations in the electrophysiological properties of myocytes across the left ventricular wall play an important role in both the normal physiology of the heart and the genesis of arrhythmias. To investigate the possible contributions of calcium channels to transmural electrical heterogeneity, whole-cell patch-clamp recordings were made from isolated canine epicardial and endocardial left ventricular myocytes. Two major differences in Ca2+ channel properties were found between epi- and endocardial cells. First, the L-type Ca2+ current was larger in endocardial than in epicardial myocytes. The average peak current density at +10 mV in endocardial myocytes was 3.4 +/- 0.2 pA pF-1, and was 45 % higher than that in epicardium (2.3 +/- 0.1 pA pF-1). The kinetic properties of the L-type current in epi- and endocardial cells were not significantly different. Second, a low-threshold, rapidly activating and inactivating Ca2+ current that resembled the T-type current was present in all endocardial myocytes but was small or absent in epicardial myocytes. This T-like current had an average peak density of 0.5 pA pF-1 at -40 mV in endocardial cells. In most endocardial cells the T-like Ca2+ current comprised two components: a Ni2+-sensitive T-type current and a tetrodotoxin-sensitive Ca2+ current. We conclude that there are considerable regional variations in the density and properties of Ca2+ channels across the canine left ventricular wall. These variations may contribute to the overall transmural electrical heterogeneity.
左心室壁心肌细胞电生理特性的区域差异在心脏正常生理学和心律失常的发生中均起重要作用。为了研究钙通道对跨壁电不均一性的可能贡献，对分离的犬左心室心外膜和心内膜心肌细胞进行了全细胞膜片钳记录。在心外膜和心内膜细胞之间发现了钙通道特性的两个主要差异。首先，心内膜心肌细胞中的L型钙电流大于心外膜心肌细胞。心内膜心肌细胞在+10 mV时的平均峰值电流密度为3.4±0.2 pA pF-1，比心外膜（2.3±0.1 pA pF-1）高45%。心外膜和心内膜细胞中L型电流的动力学特性无显著差异。其次，所有心内膜心肌细胞中均存在一种低阈值、快速激活和失活的钙电流，类似于T型电流，但在心外膜心肌细胞中较小或不存在。这种类T电流在心内膜细胞中在-40 mV时的平均峰值密度为0.5 pA pF-1。在大多数心内膜细胞中，类T钙电流由两个成分组成：镍敏感的T型电流和河豚毒素敏感的钙电流。我们得出结论，犬左心室壁钙通道的密度和特性存在相当大的区域差异。这些差异可能导致整体跨壁电不均一性。
