title: Activation, permeability, and inhibition of astrocytic and neuronal large pore (hemi)channels.
abstract: Astrocytes and neurons express several large pore (hemi)channels that may open in response to various stimuli, allowing fluorescent dyes, ions, and cytoplasmic molecules such as ATP and glutamate to permeate. Several of these large pore (hemi)channels have similar characteristics with regard to activation, permeability, and inhibitor sensitivity. Consequently, their behaviors and roles in astrocytic and neuronal (patho)physiology remain undefined. We took advantage of the Xenopus laevis expression system to determine the individual characteristics of several large pore channels in isolation. Expression of connexins Cx26, Cx30, Cx36, or Cx43, the pannexins Px1 or Px2, or the purinergic receptor P2X7 yielded functional (hemi)channels with isoform-specific characteristics. Connexin hemichannels had distinct sensitivity to alterations of extracellular Ca(2+) and their permeability to dyes and small atomic ions (conductance) were not proportional. Px1 and Px2 exhibited conductance at positive membrane potentials, but only Px1 displayed detectable fluorescent dye uptake. P2X7, in the absence of Px1, was permeable to fluorescent dyes in an agonist-dependent manner. The large pore channels displayed overlapping sensitivity to the inhibitors Brilliant Blue, gadolinium, and carbenoxolone. These results demonstrated isoform-specific characteristics among the large pore membrane channels; an open (hemi)channel is not a nonselective channel. With these isoform-specific properties in mind, we characterized the divalent cation-sensitive permeation pathway in primary cultured astrocytes. We observed no activation of membrane conductance or Cx43-mediated dye uptake in astrocytes nor in Cx43-expressing C6 cells. Our data underscore that although Cx43-mediated transport is observed in overexpressing cell systems, such transport may not be detectable in native cells under comparable experimental conditions.
authors.affiliation: Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark.
authors.forename: Daniel Bloch
authors.initials: DB
authors.lastname: Hansen
authors.affiliation: Department of Neurology, University of Washington, Seattle, Washington 98195.
authors.forename: Zu-Cheng
authors.initials: ZC
authors.lastname: Ye
authors.affiliation: Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg, Denmark, and.
authors.forename: Kirstine
authors.initials: K
authors.lastname: Calloe
authors.affiliation: Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark.
authors.forename: Thomas Hartig
authors.initials: TH
authors.lastname: Braunstein
authors.affiliation: Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark.
authors.forename: Johannes Pauli
authors.initials: JP
authors.lastname: Hofgaard
authors.affiliation: Department of Neurology, University of Washington, Seattle, Washington 98195.
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Ransom
authors.affiliation: Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark.
authors.forename: Morten Schak
authors.initials: MS
authors.lastname: Nielsen
authors.affiliation: Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark,. Electronic address: macaulay@sund.ku.dk.
authors.forename: Nanna
authors.initials: N
authors.lastname: MacAulay
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001557:Benzenesulfonates / Q000494:pharmacology; D002229:Carbenoxolone / Q000494:pharmacology; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability; D018031:Connexin 43 / Q000378:metabolism*; D004996:Ethidium / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D005682:Gadolinium / Q000494:pharmacology; D017629:Gap Junctions / Q000378:metabolism; D008564:Membrane Potentials; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D058486:Receptors, Purinergic P2X7 / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D001557:Benzenesulfonates; D018031:Connexin 43; D005456:Fluorescent Dyes; D058486:Receptors, Purinergic P2X7; D005682:Gadolinium; D004996:Ethidium; C006796:brilliant blue; D002229:Carbenoxolone
keywords: Astrocyte; Conductance; Connexin; Electrophysiology; Fluorescent Dyes; Hemichannel; Oocyte; Pannexin; p2rx7; p2x7
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