title: Impairment of diazoxide-induced formation of reactive oxygen species and loss of cardioprotection in connexin 43 deficient mice.
abstract: Protection by ischemic preconditioning is lost in cardiomyocytes and hearts of heterozygous connexin 43 deficient (Cx43+/-) mice. Because connexin 43 (Cx43) is localized in cardiomyocyte mitochondria and mitochondrial Cx43 content is increased with ischemic preconditioning, we now tried to identify a functional defect at the level of the mitochondria in Cx43+/- mice by use of diazoxide and menadione. Diazoxide stimulates the mitochondrial formation of reactive oxygen species (ROS) and menadione generates superoxide at multiple intracellular sites; both substances elicit cardioprotection through increased ROS formation. ROS formation in response to the potassium ionophore valinomycin was also measured for comparison. Menadione (2 micromol/L) and valinomycin (10 nmol/L) induced similar ROS formation in wild-type (WT) and Cx43+/- cardiomyocytes. In contrast, diazoxide (200 micromol/L) increased ROS formation by 43+/-10% versus vehicle in WT, but only by 18+/-4% in Cx43+/- cardiomyoctes (P<0.05). Two hour-simulated ischemia and oxygenated, hypo-osmolar reperfusion reduced viability as compared with normoxia (WT: 7+/-1% versus 39+/-2%, (Cx43+/-): 8+/-1% versus 40+/-3%, P<0.01). Although menadione protected WT and Cx43+/- cardiomyocytes, diazoxide increased viability (17+/-2%, P<0.01) in WT, but not in Cx43+/- (9+/-1%). Menadione (37 microg/kg i.v.) before 30 minutes coronary occlusion and 2 hour reperfusion reduced infarct size in WT and Cx43+/- mice (24+/-4% versus 24+/-5%). In contrast, diazoxide (5 mg/kg i.v.) reduced infarct size in WT (35+/-4% versus 55+/-3% of area at risk, P<0.01), but not in Cx43+/- mice (56+/-2% versus 54+/-3%). Cardiomyocytes of Cx43+/- mice have a specific functional deficit in ROS formation in response to diazoxide and accordingly less protection.
authors.affiliation: Institut für Pathophysiologie, Universitätsklinikum Essen, Germany.
authors.forename: Frank R
authors.initials: FR
authors.lastname: Heinzel
authors.forename: Yukun
authors.initials: Y
authors.lastname: Luo
authors.forename: Xiaokui
authors.initials: X
authors.lastname: Li
authors.forename: Kerstin
authors.initials: K
authors.lastname: Boengler
authors.forename: Astrid
authors.initials: A
authors.lastname: Buechert
authors.forename: David
authors.initials: D
authors.lastname: García-Dorado
authors.forename: Fabio
authors.initials: F
authors.lastname: Di Lisa
authors.forename: Rainer
authors.initials: R
authors.lastname: Schulz
authors.forename: Gerd
authors.initials: G
authors.lastname: Heusch
mesh_terms: D000818:Animals; D018031:Connexin 43 / Q000502:physiology*; D003981:Diazoxide / Q000494:pharmacology*; D019157:Ischemic Preconditioning, Myocardial; D051379:Mice; D008929:Mitochondria, Heart / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism*; D020011:Protective Agents / Q000494:pharmacology; D017382:Reactive Oxygen Species; D014634:Valinomycin / Q000494:pharmacology; D024483:Vitamin K 3 / Q000494:pharmacology
chemical_list: D018031:Connexin 43; D020011:Protective Agents; D017382:Reactive Oxygen Species; D014634:Valinomycin; D024483:Vitamin K 3; D003981:Diazoxide