Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Cardiovasc Res. 2010 Jan 1;85(1):56-67. doi: 10.1093/cvr/cvp284.
Endocannabinoids are synthesized from lipid precursors at the plasma membranes of virtually all cell types, including cardiac myocytes. Endocannabinoids can modulate neuronal and vascular ion channels through receptor-independent actions; however, their effects on cardiac K(+) channels are unknown. This study was undertaken to determine the receptor-independent effects of endocannabinoids such as anandamide (N-arachidonoylethanolamine, AEA), 2-arachidonoylglycerol (2-AG), and endocannabinoid-related compounds such as N-palmitoylethanolamine (PEA), N-oleoylethanolamine (OEA), the endogenous lipid lysophosphatidylinositol (LPI), and the fatty acids from which some of these compounds are endogenously synthesized, on human cardiac Kv1.5 channels, which generate the ultrarapid delayed rectifier current (I(Kur)).
hKv1.5 currents (I(hKv1.5)) were recorded in mouse fibroblasts (Ltk(-) cells) by using the whole-cell patch-clamp technique. Most of these compounds inhibited I(hKv1.5) in a concentration-dependent manner, the potency being determined by the number of C atoms in the fatty acyl chain. Indeed, AEA and 2-AG, which are arachidonic acid (20:4) derivatives, exhibited the highest potency (IC(50) approximately 0.9-2.5 microM), whereas PEA, a palmitic acid (PA-16:0) derivative, exhibited the lowest potency. The inhibition was independent of cannabinoid receptor engagement and of changes in the order and microviscosity of the membrane. Furthermore, blockade induced by AEA and 2-AG was abolished upon mutation of the R487 residue, which determines the external tetraethylammonium sensitivity and is located in the external entryway of the pore. AEA significantly prolonged the duration of action potentials (APs) recorded in mouse left atria.
These results indicate that endocannabinoids block human cardiac Kv1.5 channels by interacting with an extracellular binding site, a mechanism by which these compounds regulate atrial AP shape.
内源性大麻素由几乎所有细胞类型（包括心肌细胞）的质膜中的脂质前体合成。内源性大麻素可以通过受体非依赖性作用调节神经元和血管离子通道；然而，它们对心脏 K(+)通道的影响尚不清楚。本研究旨在确定内源性大麻素类似物（如 N-花生四烯酰乙醇胺（AEA）、2-花生四烯酰甘油（2-AG））以及内源性大麻素相关化合物（如 N-棕榈酰乙醇胺（PEA）、N-油酰乙醇胺（OEA）、内源性脂质溶血磷脂酰肌醇（LPI）和其中一些化合物从内源性合成的脂肪酸）对人心脏 Kv1.5 通道的受体非依赖性作用，Kv1.5 通道产生超快延迟整流电流（I(Kur)）。
通过全细胞膜片钳技术在小鼠成纤维细胞（Ltk(-) 细胞）中记录 hKv1.5 电流（I(hKv1.5)）。这些化合物中的大多数以浓度依赖性方式抑制 I(hKv1.5)，其效力由脂肪酸链中的碳原子数决定。事实上，AEA 和 2-AG，它们是花生四烯酸（20:4）的衍生物，表现出最高的效力（IC(50)约为 0.9-2.5 μM），而 PEA，棕榈酸（PA-16:0）的衍生物，表现出最低的效力。这种抑制与大麻素受体的结合以及膜的顺序和微粘度的变化无关。此外，当突变 R487 残基（决定外部四乙铵敏感性并位于孔的外部入口处）时，AEA 和 2-AG 诱导的阻断被消除。AEA 显著延长了在小鼠左心房记录的动作电位（APs）的持续时间。
这些结果表明，内源性大麻素通过与细胞外结合位点相互作用阻断人心脏 Kv1.5 通道，这是这些化合物调节心房 AP 形状的机制。
