title: K(Ca)3.1 channel downregulation and impaired endothelium-derived hyperpolarization-type relaxation in pulmonary arteries from chronically hypoxic rats.
abstract: Calcium-activated potassium channels of small (K(Ca)2, SK) and intermediate (K(Ca)3.1, IK) conductance are involved in endothelium-dependent relaxation of pulmonary arteries. We hypothesized that the function and expression of K(Ca)2 and K(Ca)3.1 increase as a compensatory mechanism to counteract hypoxia-induced pulmonary hypertension in rats. For functional studies, pulmonary arteries were mounted in microvascular myographs for isometric tension recordings. The K(Ca) channel expression was evaluated by immunoblotting and quantitative PCR. Although ACh induced similar relaxations, the ACh-induced relaxations were abolished by the combined inhibition of nitric oxide synthase (by L-nitro-arginine, L-NOARG), cyclo-oxygenase (by indomethacin) and soluble guanylate cyclase (by ODQ) in pulmonary arteries from hypoxic rats, whereas 20 ± 6% (n = 8) maximal relaxation in response to ACh persisted in arteries from normoxic rats. Inhibiting Na(+),K(+)-ATPase with ouabain or blocking K(Ca)2 and K(Ca)3.1 channels reduced the persisting ACh-induced relaxation. In the presence of L-NOARG and indomethacin, a novel K(Ca)2 and K(Ca)3.1 channel activator, NS4591, induced concentration- and endothelium-dependent relaxations, which were markedly reduced in arteries from chronically hypoxic rats compared with arteries from normoxic rats. The mRNA levels of K(Ca)2.3 and K(Ca)3.1 were unaltered, whereas K(Ca)2.3 protein expression was upregulated and K(Ca)3.1 protein expression downregulated in pulmonary arteries from rats exposed to hypoxia. In conclusion, endothelium-dependent relaxation was conserved in pulmonary arteries from chronically hypoxic rats, while endothelium-derived hyperpolarization (EDH)-type relaxation was impaired in chronically hypoxic pulmonary small arteries despite upregulation of K(Ca)2.3 channels. Since impaired EDH-type relaxation was accompanied by K(Ca)3.1 channel protein downregulation, these findings suggest that K(Ca)3.1 channels are important for the maintenance of EDH-type relaxation.
authors.affiliation: Department of Biomedicine, Pulmonary and Cardiovascular Pharmacology, Health, Aarhus University, 8000 Aarhus C, Denmark. christel.kroigaard@farm.au.dk
authors.forename: Christel
authors.initials: C
authors.lastname: Kroigaard
authors.forename: Olga
authors.initials: O
authors.lastname: Kudryavtseva
authors.forename: Thomas
authors.initials: T
authors.lastname: Dalsgaard
authors.forename: Christine
authors.initials: C
authors.lastname: Wandall-Frostholm
authors.forename: Søren-Peter
authors.initials: SP
authors.lastname: Olesen
authors.forename: Ulf
authors.initials: U
authors.lastname: Simonsen
mesh_terms: D000818:Animals; D002908:Chronic Disease; D004195:Disease Models, Animal; D015536:Down-Regulation; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000503:physiopathology; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011651:Pulmonary Artery / Q000378:metabolism*; D051381:Rats
chemical_list: D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C491575:Kcnn4 protein, rat; D026902:Potassium Channel Blockers; D010042:Ouabain; D019001:Nitric Oxide Synthase