Function of Ca 2+ Release Channels in Purkinje Cells That Survive in the Infarcted Canine Heart

Abstract

Background— Triggered Purkinje ectopy can lead to the initiation of serious ventricular arrhythmias in post–myocardial infarction patients. In the canine model, Purkinje cells from the subendocardial border of the healing infarcted heart can initiate ventricular arrhythmias. Intracellular Ca 2+ abnormalities underlie these arrhythmias, yet the subcellular reasons for these abnormalities remain unknown. Methods and Results— Using 2D confocal microscopy, we directly quantify and compare typical spontaneous Ca 2+ events in specific subcellular regions of normal Purkinje cells with those Purkinje cells from the subendocardium of the 48-hour infarcted canine heart (IZPCs). The Ca 2+ event rate was higher in the subsarcolemmal region of IZPCs when compared with normal Purkinje cells; IZPC amplitudes were higher, yet the spatial extents of these events were similar. The amplitude of caffeine-releasable Ca 2+ in either the subsarcolemmal or core regions of IZPCs did not differ from normal Purkinje cells, suggesting that Ca 2+ overload was not related to the frequency change. In permeabilized Purkinje cells from both groups, the event rate was related to free [Ca 2+ ] in both subsarcolemmal and core, but in IZPCs, this event rate was significantly increased at each free Ca 2+ , suggesting an enhanced sensitivity to Ca 2+ release. Furthermore, decays of wide long lasting Ca 2+ release events in IZPC’s core were significantly accelerated compared with those in normal Purkinje cells. JTV519 (K201) suppressed IZPC cell wide Ca 2+ waves as well as normalized the enhanced event rate and its response to free Ca 2+ . Conclusions— Increased spontaneous Ca 2+ release events in IZPCs are due to uniform regionally increased Ca 2+ release channel sensitivity to Ca 2+ without a change in sarcoplasmic reticulum content. In addition, Ca 2+ reuptake in IZPCs is accelerated. These properties would lower the threshold of Ca 2+ release channels, setting the stage for the highly frequent arrhythmogenic cell wide Ca 2+ waves observed in IZPCs.