title: Block of human heart hH1 sodium channels by amitriptyline.
abstract: Amitriptyline is a tricyclic antidepressant used to treat major depression and various neuropathic pain syndromes. This drug also causes cardiac toxicity in patients with overdose. We characterized the tonic and use-dependent amitriptyline block of human cardiac (hH1) Na(+) channels expressed in human embryonic kidney cells under voltage-clamp conditions. Our results show that, near the therapeutic plasma concentration of 1 microM, amitriptyline is an effective use-dependent blocker of hH1 Na(+) channels during repetitive pulses (approximately 55% block at 5 Hz). The tonic block for resting and for inactivated hH1 channels by amitriptyline (0.1-100 microM) yielded IC(50) values (50% inhibitory concentration) of 24.8 +/- 2.0 (n = 9) and 0.58 +/- 0.03 microM (n = 7), respectively. Substitution of phenylalanine with lysine at the hH1-F1760 position, a putative binding site for local anesthetics, eliminates the use-dependent block by amitriptyline at 1 microM. The time constants of recovery from the inactivated-state amitriptyline block in hH1 wild-type and hH1-F1760K mutant channels are 8.0 +/- 0. 5 (n = 6) and 0.45 +/- 0.07 s (n = 6), respectively. A substitution at either hH1-F1760K or hH1-Y1767K significantly increases the IC(50) values for resting and inactivated states of amitriptyline, but the increase is much more pronounced with the hH1-F1760K mutation. Because these two residues were proposed to form a part of the local anesthetic binding site, we conclude that amitriptyline and local anesthetics interact with a common binding site. Furthermore, at therapeutic concentrations, the ability of amitriptyline to act as a potent use-dependent blocker of Na(+) channels may, in part, explain its analgesic actions.
authors.affiliation: Department of Anesthesia, Harvard Medical School and Brigham & Women's Hospital, Boston, Massachusetts, USA.
authors.forename: C
authors.initials: C
authors.lastname: Nau
authors.forename: M
authors.initials: M
authors.lastname: Seaver
authors.forename: S Y
authors.initials: SY
authors.lastname: Wang
authors.forename: G K
authors.initials: GK
authors.lastname: Wang
mesh_terms: D000639:Amitriptyline / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D000779:Anesthetics, Local / Q000494:pharmacology; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects*; D006801:Humans; D017433:Protein Structure, Secondary; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000378:metabolism
chemical_list: D000779:Anesthetics, Local; D000929:Antidepressive Agents, Tricyclic; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D000639:Amitriptyline