Reduction of infarct size with D-myo-inositol trisphosphate:: role of PI3-kinase and mitochondrial KATP channels

Prophylactic treatment with (D)-myo-inositol 1,4,5- trisphosphate hexasodium [(D)-myo-Ins(1,4,5) P-3], the sodium salt of the endogenous second messenger Ins( 1,4,5) P3, triggers a reduction of infarct size comparable in magnitude to that seen with ischemic preconditioning (PC). However, the mechanisms underlying (D)-myo-Ins(1,4,5) P-3-induced protection are unknown. Accordingly, our aim was to investigate the role of four archetypal mediators implicated in PC and other cardioprotective strategies (i.e., PKC, PI3- kinase/Akt, and mitochondrial and/or sarcolemmal K-ATP channels) in the infarct-sparing effect of D-myo-Ins(1,4,5)P-3. Fifteen groups of isolated buffer-perfused rabbit hearts [5 treated with D-myo-Ins(1,4,5) P3, 5 treated with PC, and 5 control cohorts] underwent 30 min of coronary artery occlusion and 2 h of reflow. One set of control, D-myo-Ins(1,4,5) P-3, and PC groups received no additional treatment, whereas the remaining sets were infused with chelerythrine, LY294002, 5- hydroxydecanoate (5- HD), or HMR- 1098 [ inhibitors of PKC, PI3- kinase, and mitochondrial and sarcolemmal ATP- sensitive K+ (K-ATP) channels, respectively]. Infarct size (delineated by tetrazolium staining) was, as expected, significantly reduced in both D-myo-Ins(1,4,5)P-3- and PC-treated hearts versus controls. (D)-myo-Ins(1,4,5) P-3-induced cardioprotection was blocked by 5-HD but not HMR- 1098, thereby implicating the involvement of mitochondrial, but not sarcolemmal, KATP channels. Moreover, the benefits of D-myo-Ins(1,4,5)P-3 were abrogated by LY-294002, whereas, in contrast, chelerythrine had no effect. These latter pharmacological data were corroborated by immunoblotting: D-myo-Ins(1,4,5)P-3 evoked a significant increase in expression of phospho-Akt but had no effect on the activation/translocation of the cardioprotective epsilon-isoform of PKC. Thus PI3-kinase/Akt signaling and mitochondrial KATP channels participate in the reduction of infarct size afforded by prophylactic administration of D- myo- Ins( 1,4,5) P-3.