Cardiac ischemia/Reperfusion (I/R) Injury: Relative roles of sarcoplasmic reticulum (SR) Ca2+ leak and SR Ca2+ reuptake.

CIOCCI PARDO, ALEJANDRO; VALVERDE, CARLOS A; MOSCA, SUSANA; CELY-ORTIZ, ALEJANDRA; MATTIAZZI A

Mar del Plata

Congreso; Reunión Conjunta de SAIC-SAFIS-SAI 2018; 2018

SAIC - SAFIS - SAI

Although the factors contributing to I/Rinjury are complex, experimental evidence reveals that loss of Ca2+homeostasis is one of the major contributing mechanisms. Previous experimentsindicate that there are two main factors related to Ca2+ handlinginvolved in I/R cardiac injury: SR Ca2+ leak due to phosphorylationof the ryanodine receptors (RyR2) by the Ca-calmodulin dependent protein kinase(CaMKII) at the onset of reperfusion; and the increased Ca2+sequestration/load that involves CaMKII-dependent phosphorylation of phospholamban(PLN), which, when phosphorylated, increases SR Ca-ATPase activity and Ca2+sequestration. For dissecting the relative roles of these factors on mitochondrialdysfunction during I/R, experiments were performed in wild type (WT) mice,double mutant mice (SDKO), with increased SR Ca2+ leak, due toconstitutive pseudophosphorylation of RyR2 (aspartic acid replaces serine atRyR2?2814, the CaMKII site) and increased SR Ca2+ reuptake by PLN ablation,and double mutant mice (SAKO) with non-phosphorylatable CaMKII site at theRyR2, by replacement of Ser2814 site by Ala and PLN ablation. Mitochondria wereisolated from hearts non-submitted and submitted to I/R (15/10 min). Afterisolation, mitochondrial membrane potential (ΔΨm) expressed in mV and measuredby rhodamine-123 fluorescence quenching) and mitochondrial swelling (lightscattering decrease (LSD, in au)), were evaluated. In mitochondria notsubmitted to I/R there was no differences in ΔΨm among the groups. The shortprotocol of I/R significantly increased mitochondrial depolarization in SDKO(-114.6±3.1) vs. WT (-137.4±1.4). ΔΨm returned to WT values in SAKO(-143.2±2.28). LSD produced by addition of Ca2+ was alsosignificantly lower in SDKO (0.21±0.04) vs. WT (1.04±0.12) and SAKO (0.95±0.03)after I/R. The results indicated that the enhanced Ca2+ leak due toCaMKII-dependent phosphorylation of RyR2 is more important in determiningmitochondrial dysfunction in I/R than the increase in SR Ca2+reuptake by PLN ablation.