title: Astrocytic gap junction blockade markedly increases extracellular potassium without causing seizures in the mouse neocortex.
abstract: Extracellular potassium concentration, [K+]o, is a major determinant of neuronal excitability. In the healthy brain, [K+]olevels are tightly controlled. During seizures, [K+]oincreases up to 15mM and is thought to cause seizures due to its depolarizing effect. Although astrocytes have been suggested to play a key role in the redistribution (or spatial buffering) of excess K+through Connexin-43 (Cx43)-based Gap Junctions (GJs), the relation between this dynamic regulatory process and seizure generation remains unknown. Here we contrasted the role of astrocytic GJs and hemichannels by studying the effect of GJ and hemichannel blockers on [K+]oregulation in vivo. [K+]owas measured by K+-sensitive microelectrodes. Neuronal excitability was estimated by local field potential (LFP) responses to forepaw stimulation and changes in the power of resting state activity. Starting at the baseline [K+]olevel of 1.61±0.3mM, cortical microinjection of CBX, a broad spectrum connexin channel blocker, increased [K+]oto 11±3mM, Cx43 GJ/hemichannel blocker Gap27 increased it from 1.9±0.7 to 9±1mM. At these [K+]olevels, no seizures were observed. Cx43 hemichannel blockade with TAT-Gap19 increased [K+]oby only ~1mM. Microinjection of 4-aminopyridine, a known convulsant, increased [K+]oto ~10mM and induced spontaneously recurring seizures, whereas direct application of K+did not trigger seizure activity. These findings are the first in vivo demonstration that astrocytic GJs are major determinants for the spatial buffering of [K+]oand that an increase in [K+]oalone does not trigger seizures in the neocortex.
authors.affiliation: Fundamental Neurobiology, Krembil Research Institute, University Health Network, M5T 2S8 Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, M4N 3M5 Toronto, Ontario, Canada. Electronic address: paolo.bazzigaluppi@gmail.com.
authors.forename: Paolo
authors.initials: P
authors.lastname: Bazzigaluppi
authors.affiliation: Fundamental Neurobiology, Krembil Research Institute, University Health Network, M5T 2S8 Toronto, Ontario, Canada.
authors.forename: Iliya
authors.initials: I
authors.lastname: Weisspapir
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, M4N 3M5 Toronto, Ontario, Canada; Department of Medical Biophysics, University of Toronto, Ontario, Canada.
authors.forename: Bojana
authors.initials: B
authors.lastname: Stefanovic
authors.affiliation: Department of Basic Medical Sciences, University of Ghent, 9000 Ghent, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Leybaert
authors.affiliation: Fundamental Neurobiology, Krembil Research Institute, University Health Network, M5T 2S8 Toronto, Ontario, Canada.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Carlen
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002414:Cations, Monovalent / Q000378:metabolism; D018031:Connexin 43 / Q000037:antagonists & inhibitors / Q000378:metabolism; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects / Q000502:physiology; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D019579:Neocortex / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D012640:Seizures / Q000378:metabolism
chemical_list: D002414:Cations, Monovalent; D018031:Connexin 43; D015221:Potassium Channels; D011188:Potassium
keywords: 4-AP; Extracellular potassium; GAP27; Seizures; TAT-GAP19; in vivo