Abstract 2729: Experimental and Computational Evidences for Dual Alteration of Sarcoplasmic Reticulum Function in Arrhythmogenic Purkinje Cells After Myocardial Infarction
Purkinje ectopy generates premature ventricular beats and can be the onset of serious VTs in post-MI patients. Purkinje cells (Pcells) isolated from the endocardial border zone of the infarct (IZPCs) are the source of the ectopy. Intracellular Ca-elevations cause DADs and nondriven APs in Pcells. The increased frequency of large spontaneous Ca-waves (CWWs) is considered the “cellular mediator” of post-MI VTs. We sought to clarify the molecular origin of the high frequency of IZPCs CWWs. In the current study, spontaneous Ca-events were used as “functional indicators” of SR-protein complexes and were analyzed by line scan confocal microscopy in normal noninfarcted Pcells (NZPCs) (n = 19 cells) and IZPCs (n = 20) from adult mongrel dogs. Compared to NZPCs, IZPCs showed Ca-wavelets with 20% slower velocity, 50% larger amplitude, and 20% faster decay (P < 0.05). CWWs were 10% more frequent in IZPCs, exhibited a 25% faster Ca-decay and 30% increased velocity. Spark rate was increased (165%) in IZPCs. Our previous model of Ca2+ dynamics could reproduce the large amplitude and slower propagation of IZPCs wavelets when Ca2+ release pulse amplitude was increased by 50% and the threshold of Ca-release decreased 10-fold. These observations were interpreted as the result of an elevation of RyR3 conductance possibly mediated by a change in molecular structure. This structural re-arrangement of RyR3 could also impact the “Ca-sensor” of the channel and explain the elevation of RyR3 Ca-sensitivity suggested by the slower velocity of the wavelets. Acceleration of decay of IZPC wavelets was reproduced only when Ca-uptake rate was increased by 60%. This potential increase of SERCA activity in IZPCs was further supported when the same alteration of Ca-uptake was used and reproduced accurately the experimental finding of faster Ca-decline in IZPC CWWs. Enhanced spark rate and velocity of IZPC CWWs were consistent with higher Ca-sensitivity of RyR2 release. Our results support the conclusion that increased frequency of CWWs in IZPCs is due to the combination of increased RyR2 Ca-sensitivity, augmentation of RyR3 conductance and elevation of SR-Ca-uptake. Our results differ greatly from Ca protein/transient findings in ventricular cells from hearts remodeled by other diseases.