Dual calcium-voltage optical mapping of regional voltage and calcium signals in intact murine RyR2-R2474S hearts

Abnormal regional variations in electrical and calcium homeostasis properties have been implicated in catecholaminergic polymorphic ventricular tachycardias (CPVT) attributable to abnormal RyR2-mediated store Ca²⁺ release, but their underlying mechanism have not been well explored in intact hearts.

Methods

We performed in vivo and ex vivo studies including high throughput mapping of Ca²⁺ transients (CaT) and transmembrane voltage (V_m) in murine wild-type (WT) and heterozygous RyR2-R2474S/+ hearts, before and during isoprenaline (ISO) challenge.

Results

ISO-challenged RyR2-R2474S/+ showed increased incidence of arrhythmia accompanied by abnormal Ca²⁺ transients compared to WT. CaT duration (CaTD) in the LV apex amongst regions studied both before and during ISO challenge in both WT and RyR2-R2474S/+ ventricles. RyR2-R2474S/+ ventricles showed prolonged CaTD, both before and during isoprenaline (ISO) challenge. Conversely, action potential durations (APD) were the same in WT and RyR2-R2474S/+ ventricles and identically reduced by ISO challenge. RyR2-R2474S/+ showed V_m-CaT latencies at time to half decay, but not rise time to peak, which were significantly prolonged compared to WT in all ventricular regions examined with ISO challenge. Following burst pacing, ventricular localized concordant alternans in CaT and APD were readily observed in RyR2-R2474S/+ but not in WT mice. Such CaT and APD alternans occurred mostly semiannually in specific regions of the ventricular pre-occurrence of VT.

Conclusion

The pro-arrhythmic RyR2-R2474S/+ phenotype in intact hearts thus directly parallels delayed regional CaT recovery properties and alteration of V_m-CaT latencies. Studies suggest that discordant localized calcium alternans are mechanistically responsible for action potential duration alternans and occurrence of VT in RyR2-R2474S/+ mice.