Infarct limitation by a protein kinase G activator at reperfusion in rabbit hearts is dependent on sensitizing the heart to A2b agonists by protein kinase C.
PKG activator 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (CPT) at reperfusion protects ischemic hearts, but the mechanism is unknown. We recently proposed that in preconditioned hearts PKC lowers the threshold for adenosine to initiate signaling from low-affinity A2b receptors during early reperfusion thus allowing endogenous adenosine to activate survival kinases phosphatidylinositol 3-kinase (PI3K) and ERK. We tested whether CPT might also sensitize A2b receptors to adenosine. CPT (10 microM) during the first minutes of reperfusion markedly reduced infarction in isolated rabbit hearts undergoing 30-min regional ischemia/2-h reperfusion, and salvage was blocked by MRS 1754, an A2b-selective antagonist. Coadministration of wortmannin (PI3K inhibitor) or PD-98059 (MEK1/2 and therefore ERK1/2 inhibitor) also blocked protection. In nonischemic hearts, 10-min infusion of CPT did not change phosphorylation of Akt or ERK1/2. Neither did a subthreshold dose (2.5 nM) of the nonselective but A2b-potent receptor agonist 5'-(N-ethylcarboxamido)adenosine (NECA). However, when 2.5 nM NECA was combined with 10 microM CPT, both phospho-Akt and phospho-ERK1/2 significantly increased, indicating CPT had lowered the threshold for A2b-dependent signaling. The PKC antagonist chelerythrine blocked this phosphorylation induced by CPT + NECA. Chelerythrine also blocked the anti-infarct effect of CPT as did nonselective (glibenclamide) and mitochondrial-selective (5-hydroxydecanoate) K(ATP) channel blockers. A free radical scavenger, N-(2-mercaptopropionyl)glycine, also blocked CPT protection. We propose CPT targets PKG, which activates PKC through mitochondrial K(ATP) channel (mitoKATP)-dependent redox signaling, a sequence mimicking that already documented in preconditioning. Activated PKC then augments sensitivity of normally low-affinity cardiac adenosine A2b receptors so endogenous adenosine can protect by activating Akt and ERK.
Kuno
Atsushi
A
Department of Physiology, University of South Alabama, College of Medicine, Mobile, AL 36688, USA.
Solenkova
Nataliya V
NV
Solodushko
Victoriya
V
Dost
Turhan
T
Liu
Yanping
Y
Yang
Xi-Ming
XM
Cohen
Michael V
MV
Downey
James M
JM
D058908:Adenosine A2 Receptor Agonists; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D003326:Coronary Circulation / Q000187:drug effects; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000627:therapeutic use; D017869:Cyclic GMP-Dependent Protein Kinases / Q000502:physiology*; D020536:Enzyme Activators / Q000627:therapeutic use*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D009203:Myocardial Infarction / Q000188:drug therapy* / Q000209:etiology / Q000473:pathology; D015428:Myocardial Reperfusion Injury / Q000150:complications / Q000188:drug therapy* / Q000473:pathology; D009206:Myocardium / Q000201:enzymology / Q000473:pathology*; D011493:Protein Kinase C / Q000502:physiology*; D011817:Rabbits; D013873:Thionucleotides / Q000627:therapeutic use*
D058908:Adenosine A2 Receptor Agonists; D020536:Enzyme Activators; D013873:Thionucleotides; C055656:8-((4-chlorophenyl)thio)cyclic-3',5'-GMP; D017869:Cyclic GMP-Dependent Protein Kinases; D011493:Protein Kinase C; D006152:Cyclic GMP