title: Activation of endothelial IKCa channels underlies NO-dependent myoendothelial feedback.
abstract: Agonist-induced vasoconstriction triggers a negative feedback response whereby movement of charged ions through gap junctions and/or release of endothelium-derived (NO) limit further reductions in diameter, a mechanism termed myoendothelial feedback. Recent studies indicate that electrical myoendothelial feedback can be accounted for by flux of inositol trisphosphate (IP3) through myoendothelial gap junctions resulting in localized increases in endothelial Ca(2+) to activate intermediate conductance calcium-activated potassium (IKCa) channels, the resultant hyperpolarization then conducting back to the smooth muscle to attenuate agonist-induced depolarization and tone. In the present study we tested the hypothesis that activation of IKCa channels underlies NO-mediated myoendothelial feedback. Functional experiments showed that block of IP3 receptors, IKCa channels, gap junctions and transient receptor potential canonical type-3 (TRPC3) channels caused endothelium-dependent potentiation of agonist-induced increase in tone which was not additive with that caused by inhibition of NO synthase supporting a role for these proteins in NO-mediated myoendothelial feedback. Localized densities of IKCa and TRPC3 channels occurred at the internal elastic lamina/endothelial-smooth muscle interface in rat basilar arteries, potential communication sites between the two cell layers. Smooth muscle depolarization to contractile agonists was accompanied by IKCa channel-mediated endothelial hyperpolarization providing the first demonstration of IKCa channel-mediated hyperpolarization of the endothelium in response to contractile agonists. Inhibition of IKCa channels, gap junctions, TRPC3 channels or NO synthase potentiated smooth muscle depolarization to agonists in a non-additive manner. Together these data indicate that rather being distinct pathways for the modulation of smooth muscle tone, NO and endothelial IKCa channels are involved in an integrated mechanism for the regulation of agonist-induced vasoconstriction.
authors.affiliation: Faculty of Health and Community Studies, MacEwan University, Robbins Health Learning Centre, Edmonton, Alberta T5J 4S2, Canada. Electronic address: kerrp7@macewan.ca.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Kerr
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AlbertaT6G 2H7, Canada. Electronic address: rwei1@ualberta.ca.
authors.forename: Ran
authors.initials: R
authors.lastname: Wei
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AlbertaT6G 2H7, Canada. Electronic address: rtam@ualberta.ca.
authors.forename: Raymond
authors.initials: R
authors.lastname: Tam
authors.affiliation: Inflammation and Healing Cluster, Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Maroochydore, Queensland 4558, Australia. Electronic address: ssandow@usc.edu.au.
authors.forename: Shaun L
authors.initials: SL
authors.lastname: Sandow
authors.affiliation: Department of Physiology, School of Medical Sciences, University of New South Wales, Sydney, NSW2052, Australia. Electronic address: tim.murphy@unsw.edu.au.
authors.forename: Timothy V
authors.initials: TV
authors.lastname: Murphy
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AlbertaT6G 2H7, Canada. Electronic address: ondrusov@ualberta.ca.
authors.forename: Katarina
authors.initials: K
authors.lastname: Ondrusova
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AlbertaT6G 2H7, Canada. Electronic address: slunn@ualberta.ca.
authors.forename: Stephanie E
authors.initials: SE
authors.lastname: Lunn
authors.affiliation: Hotchkiss Brain and Libin Cardiovascular Research Institutes, Department of Physiology & Pharmacology, University of Calgary, AlbertaT2N-4N1, Canada. Electronic address: chttran@ucalgary.ca.
authors.forename: Cam Ha T
authors.initials: CHT
authors.lastname: Tran
authors.affiliation: Hotchkiss Brain and Libin Cardiovascular Research Institutes, Department of Physiology & Pharmacology, University of Calgary, AlbertaT2N-4N1, Canada. Electronic address: dwelsh@ucalgary.ca.
authors.forename: Donald G
authors.initials: DG
authors.lastname: Welsh
authors.affiliation: Cardiovascular Research Centre, University of Alberta, Edmonton, AlbertaT6G 2H7, Canada; Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AlbertaT6G 2H7, Canada. Electronic address: fplane@ualberta.ca.
authors.forename: Frances
authors.initials: F
authors.lastname: Plane
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D042783:Endothelial Cells / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000378:metabolism*; D017629:Gap Junctions / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D050052:TRPC Cation Channels / Q000378:metabolism; D014661:Vasoconstriction / Q000502:physiology
chemical_list: D024681:Potassium Channels, Calcium-Activated; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; D009569:Nitric Oxide; D002118:Calcium
keywords: IK(Ca) channel; IP(3) receptor; Myoendothelial feedback; NO; TRPC3