title: Halothane inhibition of recombinant cardiac L-type Ca2+ channels expressed in HEK-293 cells.
abstract: BACKGROUND
  Volatile anesthetics depress cardiac contractility, which involves inhibition of cardiac L-type calcium channels. To explore the role of voltage-dependent inactivation, the authors analyzed halothane effects on recombinant cardiac L-type calcium channels (alpha1Cbeta2a and alpha1Cbeta2aalpha2/delta1), which differ by the alpha2/delta1 subunit and consequently voltage-dependent inactivation.
  
  
  METHODS
  HEK-293 cells were transiently cotransfected with complementary DNAs encoding alpha1C tagged with green fluorescent protein and beta2a, with and without alpha2/delta1. Halothane effects on macroscopic barium currents were recorded using patch clamp methodology from cells expressing alpha1Cbeta2a and alpha1Cbeta2aalpha2/delta1 as identified by fluorescence microscopy.
  
  
  RESULTS
  Halothane inhibited peak current (I(peak)) and enhanced apparent inactivation (reported by end pulse current amplitude of 300-ms depolarizations [I300]) in a concentration-dependent manner in both channel types. alpha2/delta1 coexpression shifted relations leftward as reported by the 50% inhibitory concentration of I(peak) and I300/I(peak)for alpha1Cbeta2a (1.8 and 14.5 mm, respectively) and alpha1Cbeta2aalpha2/delta1 (0.74 and 1.36 mm, respectively). Halothane reduced transmembrane charge transfer primarily through I(peak) depression and not by enhancement of macroscopic inactivation for both channels.
  
  
  CONCLUSIONS
  The results indicate that phenotypic features arising from alpha2/delta1 coexpression play a key role in halothane inhibition of cardiac L-type calcium channels. These features included marked effects on I(peak) inhibition, which is the principal determinant of charge transfer reductions. I(peak) depression arises primarily from transitions to nonactivatable states at resting membrane potentials. The findings point to the importance of halothane interactions with states present at resting membrane potential and discount the role of inactivation apparent in current time courses in determining transmembrane charge transfer.
authors.affiliation: Department of Anesthesiology, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA. kevin.gingrich@med.nyu.edu
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Gingrich
authors.forename: Son
authors.initials: S
authors.lastname: Tran
authors.forename: Igor M
authors.initials: IM
authors.lastname: Nikonorov
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Blanck
mesh_terms: D000465:Algorithms; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D001711:Biotransformation / Q000187:drug effects; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D002460:Cell Line; D004594:Electrophysiology; D006221:Halothane / Q000494:pharmacology*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009419:Nerve Tissue Proteins / Q000187:drug effects; D018408:Patch-Clamp Techniques
chemical_list: D018685:Anesthetics, Inhalation; C079146:CACNA1C protein, human; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D009419:Nerve Tissue Proteins; D006221:Halothane