title: Gap junctions support the sustained phase of hypoxic pulmonary vasoconstriction by facilitating calcium sensitization.
abstract: OBJECTIVE
  To determine the role of gap junctions (GJs) in hypoxic pulmonary vasoconstriction (HPV).
  
  
  RESULTS
  Studies were performed in rat isolated intrapulmonary arteries (IPAs) mounted on a myograph and in anaesthetized rats. Hypoxia induced a biphasic HPV response in IPAs preconstricted with prostaglandin F2α (PGF2α, 3 µM) or 20 mM K⁺. The GJ inhibitors 18β-glycyrrhetinic acid (18β-GA, 30 µM), heptanol (3.5 mM), or 2-aminoethoxydiphenyl borate (2-APB) (75 µM) had little effect on the transient Phase 1 of HPV, but abolished the sustained Phase 2 which is associated with Ca²⁺ sensitization. The voltage-dependent Ca²⁺ channel blocker diltiazem (10 µM) had no effect on HPV, and did not alter the inhibitory action of 18β-GA. Sustained HPV is enhanced by high glucose (15 mM) via potentiation of Ca²⁺ sensitization, in the presence of high glucose 18β-GA still abolished sustained HPV. Simultaneous measurement of tension and intracellular Ca²⁺ using Fura PE-3 demonstrated that whilst 18β-GA abolished tension development during sustained HPV, it did not affect the elevation of intracellular Ca²⁺. Consistent with this, 18β-GA abolished hypoxia-induced phosphorylation of the Rho kinase target MYPT-1. In anaesthetized rats hypoxia caused a biphasic increase in systolic right ventricular pressure. Treatment with oral 18β-GA (25 mg/kg) abolished the sustained component of the hypoxic pressor response.
  
  
  CONCLUSIONS
  These results imply that GJs are critically involved in the signalling pathways leading to Rho kinase-dependent Ca²⁺ sensitization during sustained HPV, but not elevation of intracellular Ca²⁺, and may explain the dependence of the former on an intact endothelium.
authors.affiliation: Department of Experimental Therapeutics, Institute of Pharmacology and Toxicology of National Academy of Medical Sciences of Ukraine, Kiev, Ukraine.
authors.forename: Igor V
authors.initials: IV
authors.lastname: Kizub
authors.forename: Ievgen V
authors.initials: IV
authors.lastname: Strielkov
authors.forename: Yasin
authors.initials: Y
authors.lastname: Shaifta
authors.forename: Silke
authors.initials: S
authors.lastname: Becker
authors.forename: Jesus
authors.initials: J
authors.lastname: Prieto-Lloret
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Snetkov
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Soloviev
authors.forename: Philip I
authors.initials: PI
authors.lastname: Aaronson
authors.forename: Jeremy P T
authors.initials: JP
authors.lastname: Ward
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D006034:Glycyrrhetinic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D010766:Phosphorylation; D054645:Protein Phosphatase 1 / Q000378:metabolism; D011651:Pulmonary Artery / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*; D054460:rho-Associated Kinases / Q000378:metabolism
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; C119129:18alpha-glycyrrhetinic acid; D054460:rho-Associated Kinases; C499850:Ppp1r12a protein, rat; D054645:Protein Phosphatase 1; D004110:Diltiazem; D006034:Glycyrrhetinic Acid; D002118:Calcium
keywords: 18β-glycyrrhetinic acid; Ca2+ sensitization; Gap junctions; Hypoxic pulmonary vasoconstriction; Pulmonary artery