Cardiovascular Research Advance Access first published online on August 18, 2009
This version [Corrected Proof] published online on September 11, 2009
Cardiovascular Research, doi:10.1093/cvr/cvp284
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Endocannabinoids and cannabinoid analogues block cardiac hKv1.5 channels in a cannabinoid receptor-independent manner
1 Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, 28040 Madrid, Spain
2 Instituto de Química Física Rocasolano (CSIC), Madrid, Spain
3 Department of Biochemistry and Molecular Biology I, School of Biology, Universidad Complutense de Madrid, Madrid, Spain
* Corresponding author. Tel: +34 91 394 1474, Fax: +34 91 394 1470, Email: rcaballero{at}med.ucm.es
Aims: 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 (IKur).
Methods and results: hKv1.5 currents (IhKv1.5) were recorded in mouse fibroblasts (Ltk– cells) by using the whole-cell patch-clamp technique. Most of these compounds inhibited IhKv1.5 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 (IC50
0.9–2.5 µM), 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.
Conclusion: 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.
KEYWORDS Anandamide; 2-arachidonoylglycerol; Kv1.5; Endocannabinoids; Fatty acids; Arachidonic acid; Cardiac potassium channels
Time for primary review: 30 days
Both authors contributed equally.