First molecular evidence that inositol trisphosphate signaling contributes to infarct size reduction with preconditioning

Abstract

Considerable attention has focused on the role of protein kinase C (PKC) in triggering the profound infarct-sparing effect of ischemic preconditioning (PC). In contrast, the involvement of inositol 1,4,5-trisphosphate [Ins( 1 , 4 , 5 )P3], the second messenger generated in parallel with the diacylglycerol-PKC pathway, remains poorly understood. We hypothesized that, if Ins( 1 , 4 , 5 )P3signaling [i.e., release of Ins( 1 , 4 , 5 )P3and subsequent binding to Ins( 1 , 4 , 5 )P3receptors] contributes to PC-induced cardioprotection, then the reduction of infarct size achieved with PC would be attenuated in mice that are deficient in Ins( 1 , 4 , 5 )P3receptor protein. To test this concept, hearts were harvested from 1) B6C3Fe- a/a-Itpr-1opt+/−/J mutants displaying reduced expression of Ins( 1 , 4 , 5 )P3receptor-1 protein, 2) Itpr-1opt+/+wild types from the colony, and 3) C57BL/6J mice. All hearts were buffer-perfused and randomized to receive two 5-min episodes of PC ischemia, pretreatment with d- myo-Ins( 1 , 4 , 5 )P3[sodium salt of native Ins( 1 , 4 , 5 )P3], the mitochondrial ATP-sensitive K+channel opener diazoxide, or no intervention (controls). After the treatment phase, all hearts underwent 30-min global ischemia followed by 2 h of reperfusion, and infarct size was delineated by tetrazolium staining. In both wild-type and C57BL/6J cohorts, area of necrosis in hearts that received PC, d- myo-Ins( 1 , 4 , 5 )P3, and diazoxide averaged 28–35% of the total left ventricle (LV), significantly smaller than the values of 52–53% seen in controls ( P < 0.05). In contrast, in Itpr-1opt+/−mutants, protection was only seen with diazoxide: neither PC nor d- myo-Ins( 1 , 4 , 5 )P3limited infarct size (52–58% vs. 56% of the LV in mutant controls). These data provide novel evidence that Ins( 1 , 4 , 5 )P3signaling contributes to infarct size reduction with PC.