Evidence that free polyunsaturated fatty acids modify Na+ channels by directly binding to the channel proteins.
The effects of free polyunsaturated fatty acids (PUFA) on the binding of ligands to receptors on voltage-sensitive Na+ channels of neonatal rat cardiac myocytes were assessed. The radioligand was [benzoyl-2,5-(3)H] batrachotoxinin A 20alpha-benzoate ([(3)H]BTXB), a toxin that binds to the Na+ channel. The PUFA that have been shown to be antiarrhythmic, including eicosapentaenoic acid (EPA; C20:5n-3), docosahexaenoic acid (DHA; C22:6n-3), eicosatetraynoic acid (ETYA), linolenic acid (C18:3n-3), and linoleic acid (C18:2n-6), inhibited [(3)H]BTXB binding in a dose-dependent fashion with IC50 values of 28-35 microM, whereas those fatty acids that have no antiarrhythmic effects including saturated fatty acid (stearic acid, C18:0), monounsaturated fatty acid (oleic acid; C18:1n-9), and EPA methyl ester did not have a significant effect on [(3)H]BTXB binding. Enrichment of the myocyte membrane with cholesterol neither affected [(3)H]BTXB binding when compared with control cells nor altered the inhibitory effects of PUFA on [(3)H]BTXB binding. Scatchard analysis of [(3)H]BTXB binding showed that EPA reduced the maximal binding without altering the Kd for [(3)H]BTXB binding, indicating allosteric inhibition. The inhibition by EPA of [(3)H]BTXB binding was reversible (within 30 min) when delipidated bovine serum albumin was added. The binding of the PUFA to this site on the Na+ channel is reversible and structure-specific and occurs at concentrations close to those required for apparent antiarrhythmic effects and a blocking effect on the Na+ current, suggesting that binding of the PUFA at this site relates to their antiarrhythmic action.
Kang
J X
JX
Department of Medicine, Harvard Medical School, Boston, MA 02114, USA.
Leaf
A
A
D000818:Animals; D001496:Batrachotoxins; D001665:Binding Sites; D002417:Cattle; D002478:Cells, Cultured; D005230:Fatty Acids, Nonesterified / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism; D009498:Neurotoxins; D011869:Radioligand Assay; D051381:Rats; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism*
D001496:Batrachotoxins; D005230:Fatty Acids, Nonesterified; D009498:Neurotoxins; D015222:Sodium Channels; C031775:batrachotoxinin A 20-alpha-benzoate