title: The cardiac sodium current Na(v)1.5 is functionally expressed in rabbit bronchial smooth muscle cells.
abstract: A collagenase-proteinase mixture was used to isolate airway smooth muscle cells (ASMC) from rabbit bronchi, and membrane currents were recorded using the whole cell patch-clamp technique. Stepping from -100 mV to a test potential of -40 mV evoked a fast voltage-dependent Na(+) current, sometimes with an amplitude of several nanoamperes. The current disappeared within 15 min of exposure to papain + DTT (n = 6). Comparison of the current in ASMC with current mediated by NaV1.5 α-subunits expressed in human embryonic kidney cells revealed similar voltage dependences of activation (V1/2 = -42 mV for NaV1.5) and sensitivities to TTX (IC50 = 1.1 and 1.2 μM for ASMC and NaV1.5, respectively). The current in ASMC was also blocked by lidocaine (IC50 = 160 μM). Although veratridine, an agonist of voltage-gated Na(+) channels, reduced the peak current by 33%, it slowed inactivation, resulting in a fourfold increase in sustained current (measured at 25 ms after onset). In current-clamp mode, veratridine prolonged evoked action potentials from 37 ± 9 to 1,053 ± 410 ms (n = 8). Primers for NaV1.2-1.9 were used to amplify mRNA from groups of ∼20 isolated ASMC and from whole bronchial tissue by RT-PCR. Transcripts for NaV1.2, NaV1.3, and NaV1.5-1.9 were detected in whole tissue, but only NaV1.2 and NaV1.5 were detected in single cells. We conclude that freshly dispersed rabbit ASMC express a fast voltage-gated Na(+) current that is mediated mainly by the NaV1.5 subtype.
authors.affiliation: Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
authors.forename: E
authors.initials: E
authors.lastname: Bradley
authors.forename: T I
authors.initials: TI
authors.lastname: Webb
authors.forename: M A
authors.initials: MA
authors.lastname: Hollywood
authors.forename: G P
authors.initials: GP
authors.lastname: Sergeant
authors.forename: N G
authors.initials: NG
authors.lastname: McHale
authors.forename: K D
authors.initials: KD
authors.lastname: Thornbury
mesh_terms: D000818:Animals; D001980:Bronchi / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002469:Cell Separation / Q000379:methods; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D062554:NAV1.5 Voltage-Gated Sodium Channel / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D026941:Sodium Channel Blockers / Q000494:pharmacology; D014162:Transfection
chemical_list: D062554:NAV1.5 Voltage-Gated Sodium Channel; D012333:RNA, Messenger; C568320:SCN5A protein, human; D026941:Sodium Channel Blockers
keywords: Nav1.5; airway smooth muscle; patch clamp; sodium current