Cardiac mitochondrial preconditioning by Big Ca2+-sensitive K+ channel opening requires superoxide radical generation.
ATP-sensitive K+ channel opening in inner mitochondrial membranes protects hearts from ischemia-reperfusion (I/R) injury. Opening of the Big conductance Ca2+-sensitive K+ channel (BK(Ca)) is now also known to elicit cardiac preconditioning. We investigated the role of the pharmacological opening of the BK(Ca) channel on inducing mitochondrial preconditioning during I/R and the role of O2-derived free radicals in modulating protection by putative mitochondrial (m)BK(Ca) channel opening. Left ventricular (LV) pressure (LVP) was measured with a balloon and transducer in guinea pig hearts isolated and perfused at constant pressure. NADH, reactive oxygen species (ROS), principally superoxide (O2(-*)), and m[Ca2+] were measured spectrophotofluorometrically at the LV free wall using autofluorescence and fluorescent dyes dihydroethidium and indo 1, respectively. BK(Ca) channel opener 1-(2'-hydroxy-5'-trifluoromethylphenyl)-5-trifluoromethyl-2(3H)benzimid-axolone (NS; NS-1619) was given for 15 min, ending 25 min before 30 min of global I/R. Either Mn(III)tetrakis(4-benzoic acid)porphyrin (TB; MnTBAP), a synthetic dismutator of O2(-*), or an antagonist of the BK(Ca) channel paxilline (PX) was given alone or for 5 min before, during, and 5 min after NS. NS pretreatment resulted in a 2.5-fold increase in developed LVP and a 2.5-fold decrease in infarct size. This was accompanied by less O2(-*) generation, decreased m[Ca2+], and more normalized NADH during early ischemia and throughout reperfusion. Both TB and PX antagonized each preconditioning effect. This indicates that 1) NS induces a mitochondrial-preconditioned state, evident during early ischemia, presumably on mBK(Ca) channels; 2) NS effects are blocked by BK(Ca) antagonist PX; and 3) NS-induced preconditioning is dependent on the production of ROS. Thus NS may induce mitochondrial ROS release to initiate preconditioning.
Stowe
David F
DF
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA. dfstowe@mcw.edu
Aldakkak
Mohammed
M
Camara
Amadou K S
AK
Riess
Matthias L
ML
Heinen
Andre
A
Varadarajan
Srinivasan G
SG
Jiang
Ming-Tao
MT
D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004996:Ethidium / Q000031:analogs & derivatives; D006168:Guinea Pigs; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000502:physiology*; D008929:Mitochondria, Heart / Q000502:physiology*; D009243:NAD; D017382:Reactive Oxygen Species / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*
D001562:Benzimidazoles; D051036:Large-Conductance Calcium-Activated Potassium Channels; D017382:Reactive Oxygen Species; D009243:NAD; C067883:dihydroethidium; D013481:Superoxides; C086491:NS 1619; D004996:Ethidium; D002118:Calcium