Résumé
After MI, increased spontaneous SR-Ca 2+ -releases depolarize the membrane and trigger action potentials (APs) in cardiac Purkinje cells (Pcells). This abnormal Ca 2+ -activity is involved in ventricular fibrillation. Spontaneous Ca 2+ -transients analysis suggested that intensification of SR-Ca 2+ -uptake accounts for the abnormal SR-Ca 2+ -release in post-MI Pcells. Increased SR-Ca 2+ -pump (SERCA) density, PLB-dependent Ca 2+ -pump activation, and modification of the pump Ca 2+ -transport properties can mediate an increase in SR-Ca 2+ -uptake. We examined whether Pcells of ischemic hearts show signs of these alterations, hence supporting the hypothesis of post-MI increase in SR-Ca 2+ -uptake. Methods. Pcells were prepared from hearts with and without MI in dogs, sheep, pigs, and humans. The distribution of SR-Ca 2+ -pumps and phosphorylated forms of PLB, pPLBSer16 and pPLBThr17, was captured by specific immunofluorescence and confocal microscopy. Protein and transcript levels of SERCA2 sub-isoforms were measured in Purkinje fibers and myocardium by WB and RT-qPCR, respectively. Results. In normal hearts, Ca 2+ -pumps and PLB antibodies co-localized throughout Pcells. After MI, Ca 2+ -pump staining exhibited larger intensity in peripheral compared to central regions of Pcells. Phosphorylated PLB staining was unchanged, indicating no alteration of the pump-β-adrenergic regulation after MI. Expression of the regular cardiac pump, SERCA2a, was preserved. However, the emergence of another pump, SERCA2b, was found after MI. The addition of SERCA2b to the existing SERCA2a expression increased the total pump density, which was consistent with an augmentation of SR-Ca 2+ -uptake in Pcells after MI. Conclusion. After MI, the peripheral region of Pcells seems to express the SERCA2b pump sub-isoform, which is consistent with larger pump density and intensification of SR-Ca 2+ -uptake.