title: Block of human heart hH1 sodium channels by the enantiomers of bupivacaine.
abstract: BACKGROUND
  S(-)-bupivacaine reportedly exhibits lower cardiotoxicity but similar local anesthetic potency compared with R(+)-bupivacaine. The bupivacaine binding site in human heart (hH1) Na+ channels has not been studied to date. The authors investigated the interaction of bupivacaine enantiomers with hH1 Na+ channels, assessed the contribution of putatively relevant residues to binding, and compared the intrinsic affinities to another isoform, the rat skeletal muscle (mu1) Na+ channel.
  
  
  METHODS
  Human heart and mu1 Na+ channel alpha subunits were transiently expressed in HEK293t cells and investigated during whole cell voltage-clamp conditions. Using site-directed mutagenesis, the authors created point mutations at positions hH1-F1760, hH1-N1765, hH1-Y1767, and hH1-N406 by introducing the positively charged lysine (K) or the negatively charged aspartic acid (D) and studied their influence on state-dependent block by bupivacaine enantiomers.
  
  
  RESULTS
  Inactivated hH1 Na+ channels displayed a weak stereoselectivity with a stereopotency ratio (+/-) of 1.5. In mutations hH1-F1760K and hH1-N1765K, bupivacaine affinity of inactivated channels was reduced by approximately 20- to 40-fold, in mutation hH1-N406K by approximately sevenfold, and in mutations hH1-Y1767K and hH1-Y1767D by approximately twofold to threefold. Changes in recovery of inactivated mutant channels from block paralleled those of inactivated channel affinity. Inactivated hH1 Na+ channels exhibited a slightly higher intrinsic affinity than mu1 Na+ channels.
  
  
  CONCLUSIONS
  Differences in bupivacaine stereoselectivity and intrinsic affinity between hH1 and mu1 Na+ channels are small and most likely of minor clinical relevance. Amino acid residues in positions hH1-F1760, hH1-N1765, and hH1-N406 may contribute to binding of bupivacaine enantiomers in hH1 Na+ channels, whereas the role of hH1-Y1767 remains unclear.
authors.affiliation: Department of Anesthesia Research Laboratories, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: C
authors.initials: C
authors.lastname: Nau
authors.forename: S Y
authors.initials: SY
authors.lastname: Wang
authors.forename: G R
authors.initials: GR
authors.lastname: Strichartz
authors.forename: G K
authors.initials: GK
authors.lastname: Wang
mesh_terms: D000779:Anesthetics, Local / Q000493:pharmacokinetics / Q000494:pharmacology*; D000818:Animals; D002045:Bupivacaine / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000378:metabolism / Q000502:physiology; D013237:Stereoisomerism; D014162:Transfection
chemical_list: D000779:Anesthetics, Local; D018076:DNA, Complementary; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D002045:Bupivacaine