title: Intermediate-conductance calcium-activated potassium channels participate in neurovascular coupling.
abstract: OBJECTIVE
  Controlling vascular tone involves K(+) efflux through endothelial cell small- and intermediate-conductance calcium-activated potassium channels (K(Ca)2.3 and K(Ca)3.1, respectively). We investigated the expression of these channels in astrocytes and the possibility that, by a similar mechanism, they might contribute to neurovascular coupling.
  
  
  METHODS
  Transgenic mice expressing enhanced green fluorescent protein (eGFP) in astrocytes were used to assess K(Ca)2.3 and K(Ca)3.1 expression by immunohistochemistry and RT-PCR. K(Ca) currents in eGFP-positive astrocytes were determined in situ using whole-cell patch clamp electrophysiology. The contribution of K(Ca)3.1 to neurovascular coupling was investigated in pharmacological experiments using electrical field stimulation (EFS) to evoke parenchymal arteriole dilatation in FVB/NJ mouse brain slices and whisker stimulation to evoke changes in cerebral blood flow in vivo, measured by laser Doppler flowmetry.
  
  
  RESULTS
  K(Ca)3.1 immunoreactivity was restricted to astrocyte processes and endfeet and RT-PCR confirmed astrocytic K(Ca)2.3 and K(Ca)3.1 mRNA expression. With 200 nM [Ca(2+)](i) , the K(Ca)2.1-2.3/K(Ca)3.1 opener NS309 increased whole-cell currents. CyPPA, a K(Ca)2.2/K(Ca)2.3 opener, was without effect. With 1 µM [Ca(2+)](i) , the K(Ca)3.1 inhibitor TRAM-34 reduced currents whereas apamin (K(Ca)2.1-2.3 blocker) had no effect. CyPPA also inhibited currents evoked by NS309 in HEK293 cells expressing K(Ca)3.1. EFS-evoked Fluo-4 fluorescence confirmed astrocyte endfoot recruitment into neurovascular coupling. TRAM-34 inhibited EFS-evoked arteriolar dilatation by 50% whereas charybdotoxin, a blocker of K(Ca)3.1 and the large-conductance K(Ca) channel, K(Ca)1.1, inhibited dilatation by 82%. TRAM-34 reduced the cortical hyperaemic response to whisker stimulation by 40%.
  
  
  CONCLUSIONS
  Astrocytes express functional K(Ca)3.1 channels, and these contribute to neurovascular coupling.
authors.affiliation: Faculty of Life Sciences, University of Manchester, UK. thomas.longden@uvm.edu
authors.forename: T A
authors.initials: TA
authors.lastname: Longden
authors.forename: K M
authors.initials: KM
authors.lastname: Dunn
authors.forename: H J
authors.initials: HJ
authors.lastname: Draheim
authors.forename: M T
authors.initials: MT
authors.lastname: Nelson
authors.forename: A H
authors.initials: AH
authors.lastname: Weston
authors.forename: G
authors.initials: G
authors.lastname: Edwards
mesh_terms: D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000378:metabolism; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014664:Vasodilation / Q000187:drug effects
chemical_list: D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D051640:Small-Conductance Calcium-Activated Potassium Channels; D002118:Calcium