title: Brief daily episode of normoxia inhibits cardioprotection conferred by chronic continuous hypoxia. Role of oxidative stress and BKCa channels.
abstract: The purpose of the present study was to assess the impact of brief daily reoxygenation during adaptation to chronic continuous hypoxia (CCH) on protective cardiac phenotype. Adult male Wistar rats were kept at CCH (10% oxygen) for 5, 15 or 30 days; a subgroup of animals was exposed to room air daily for a single 60-min period. While 5 days of CCH did not affect myocardial infarction induced by 20-min coronary artery occlusion and 3-h reperfusion, 15 days reduced infarct size from 62% of the area at risk in normoxic controls to 52%, and this protective effect was more pronounced after 30 days (41%). Susceptibility to ischemic ventricular arrhythmias exhibited reciprocal development. CCH increased myocardial abundance of mitochondrial superoxide dismutase (MnSOD) without affecting malondialdehyde concentration. Daily reoxygenation abolished both the infarct size-limiting effect of CCH and MnSOD upregulation, and increased malondialdehyde (by 53%). Ventricular cardiomyocytes isolated from CCH rats exhibited better survival and lower lactate dehydrogenase release caused by simulated ischemia/reperfusion than cells from normoxic and daily reoxygenated groups. The cytoprotective effects of CCH were attenuated by the large-conductance Ca2+-activated K+ (BKCa) channel blocker paxilline, while the opener NS1619 reduced cell injury in the normoxic group but not in the CCH group. Daily reoxygenation restored the NS1619- induced protection, whereas paxilline had no effect, resembling the pattern observed in the normoxic group. The results suggest that CCH is cardioprotective and brief daily reoxygenation blunts its salutary effects, possibly by a mechanism involving oxidative stress and attenuation of the activation of mitochondrial BKCa channels.
authors.affiliation: Institute of Physiology, Academy of Sciences of the Czech Republic, Videnska 1083, 142 20 Prague, Czech Republic. kolar@biomed.cas.cz.
authors.forename: Jan
authors.initials: J
authors.lastname: Neckár
authors.forename: Gudrun H
authors.initials: GH
authors.lastname: Borchert
authors.forename: Patricie
authors.initials: P
authors.lastname: Hlousková
authors.forename: Petra
authors.initials: P
authors.lastname: Mícová
authors.forename: Olga
authors.initials: O
authors.lastname: Nováková
authors.forename: Frantisek
authors.initials: F
authors.lastname: Novák
authors.forename: Milos
authors.initials: M
authors.lastname: Hroch
authors.forename: Frantisek
authors.initials: F
authors.lastname: Papousek
authors.forename: Bohuslav
authors.initials: B
authors.lastname: Ost'ádal
authors.forename: Frantisek
authors.initials: F
authors.lastname: Kolár
mesh_terms: D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D006031:Glycosylation; D000860:Hypoxia / Q000378:metabolism*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D002316:Cardiotonic Agents; C494842:Kcnma1 protein, rat; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D015221:Potassium Channels; D008315:Malondialdehyde; D013482:Superoxide Dismutase; D010100:Oxygen