title: Electrical conduction along endothelial cell tubes from mouse feed arteries: confounding actions of glycyrrhetinic acid derivatives.
abstract: OBJECTIVE
  Electrical conduction along endothelium of resistance vessels has not been determined independently of the influence of smooth muscle, surrounding tissue or blood. Two interrelated hypotheses were tested: (i) Intercellular conduction of electrical signals is manifest in endothelial cell (EC) tubes; and (ii) Inhibitors of gap junction channels (GJCs) have confounding actions on EC electrical and Ca(2+) signalling.
  
  
  METHODS
  Intact EC tubes were isolated from abdominal muscle feed (superior epigastric) arteries of C57BL/6 mice. Hyperpolarization was initiated with indirect (ACh) and direct (NS309) stimulation of intermediate- and small-conductance Ca(2+) -activated K(+) channels (IK(Ca) /SK(Ca) ). Remote membrane potential (V(m) ) responses to intracellular current injection defined the length constant (λ) for electrical conduction. Dye coupling was evaluated following intracellular microinjection of propidium iodide. Intracellular Ca(2+) dynamics were determined using Fura-2 photometry. Carbenoxolone (CBX) or β-glycyrrhetinic acid (βGA) was used to investigate the role of GJCs.
  
  
  RESULTS
  Steady-state V(m) of ECs was -25 mV. ACh and NS309 hyperpolarized ECs by -40 and -60 mV respectively. Electrical conduction decayed monoexponentially with distance (λ∼1.4 mm). Propidium iodide injected into one EC spread into surrounding ECs. CBX or βGA inhibited dye transfer, electrical conduction and EC hyperpolarization reversibly. Both agents elevated resting Ca(2+) while βGA inhibited responses to ACh.
  
  
  CONCLUSIONS
  Individual cells were effectively coupled to each other within EC tubes. Inhibiting GJCs with glycyrrhetinic acid derivatives blocked hyperpolarization mediated by IK(Ca) /SK(Ca) channels, regardless of Ca(2+) signalling, obviating use of these agents in distinguishing key determinants of electrical conduction along the endothelium.
authors.affiliation: Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65212, USA.
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Behringer
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Socha
authors.forename: Luis
authors.initials: L
authors.lastname: Polo-Parada
authors.forename: Steven S
authors.initials: SS
authors.lastname: Segal
mesh_terms: D000005:Abdomen; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology*; D002229:Carbenoxolone / Q000494:pharmacology; D004553:Electric Conductivity; D042783:Endothelial Cells / Q000187:drug effects / Q000502:physiology*; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D006034:Glycyrrhetinic Acid / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000502:physiology; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000502:physiology; D010091:Oximes / Q000494:pharmacology; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000502:physiology
chemical_list: C493327:6,7-dichloro-1H-indole-2,3-dione 3-oxime; D007211:Indoles; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496900:Kcnn3 protein, mouse; C496925:Kcnn4 protein, mouse; D010091:Oximes; D051640:Small-Conductance Calcium-Activated Potassium Channels; D002229:Carbenoxolone; D000109:Acetylcholine; D006034:Glycyrrhetinic Acid