Physiological consequences of the P2328S mutation in the ryanodine receptor ( RyR2) gene in genetically modified murine hearts.

Aim: To explore the physiological consequences of the ryanodine receptor (RyR2)- P2328S mutation associated with catecholaminergic polymorphic ventricular tachycardia (CPVT). Methods: We generated heterozygotic ( RyR2 ^p/s) and homozygotic ( RyR2 ^s/s) transgenic mice and studied Ca²⁺ signals from regularly stimulated, Fluo-3-loaded, cardiac myocytes. Results were compared with monophasic action potentials (MAPs) in Langendorff-perfused hearts under both regular and programmed electrical stimulation (PES). Results: Evoked Ca²⁺ transients from wild-type ( WT), heterozygote ( RyR2 ^p/s) and homozygote ( RyR2 ^s/s) myocytes had indistinguishable peak amplitudes with RyR2 ^s/s showing subsidiary events. Adding 100 nm isoproterenol produced both ectopic peaks and subsidiary events in WT but not RyR2 ^p/s and ectopic peaks and reduced amplitudes of evoked peaks in RyR2 ^s/s. Regularly stimulated WT, RyR2 ^p/s and RyR2 ^s/s hearts showed indistinguishable MAP durations and refractory periods. RyR2 ^p/s hearts showed non-sustained ventricular tachycardias (nsVTs) only with PES. Both nsVTs and sustained VTs (sVTs) occurred with regular stimuli and PES with isoproterenol treatment. RyR2 ^s/s hearts showed higher incidences of nsVTs before but mainly sVTs after introduction of isoproterenol with both regular stimuli and PES, particularly at higher pacing frequencies. Additionally, intrinsically beating RyR2 ^s/s showed extrasystolic events often followed by spontaneous sVT. Conclusion: The RyR2-P2328S mutation results in marked alterations in cellular Ca²⁺ homeostasis and arrhythmogenic properties resembling CPVT with greater effects in the homozygote than the heterozygote demonstrating an important gene dosage effect. [ABSTRACT FROM AUTHOR]