Endocannabinoids and cannabinoid analogues block cardiac hKv1.5 channels in a cannabinoid receptor-independent manner.
OBJECTIVE
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)).


RESULTS
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.


CONCLUSIONS
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.
Barana
Adriana
A
Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Amorós
Irene
I
Caballero
Ricardo
R
Gómez
Ricardo
R
Osuna
Lourdes
L
Lillo
M Pilar
MP
Blázquez
Cristina
C
Guzmán
Manuel
M
Delpón
Eva
E
Tamargo
Juan
J
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D063385:Cannabinoid Receptor Modulators / Q000494:pharmacology*; D002186:Cannabinoids / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D063388:Endocannabinoids; D005227:Fatty Acids / Q000494:pharmacology; D005454:Fluorescence Polarization; D006321:Heart / Q000187:drug effects*; D006801:Humans; D051666:Kv1.5 Potassium Channel / Q000037:antagonists & inhibitors*; D051379:Mice; D053284:Polyunsaturated Alkamides / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology; D043882:Receptors, Cannabinoid / Q000502:physiology*
D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D002186:Cannabinoids; D063388:Endocannabinoids; D005227:Fatty Acids; C496981:KCNA5 protein, human; D051666:Kv1.5 Potassium Channel; D053284:Polyunsaturated Alkamides; D043882:Receptors, Cannabinoid; D011493:Protein Kinase C; D002118:Calcium; C078814:anandamide