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


CONCLUSIONS
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.
Goddard
C A
CA
Physiological Laboratory, University of Cambridge, Cambridge, UK.
Ghais
N S
NS
Zhang
Y
Y
Williams
A J
AJ
Colledge
W H
WH
Grace
A A
AA
Huang
C L-H
CL
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002304:Cardiac Pacing, Artificial / Q000379:methods; D002478:Cells, Cultured; D006579:Heterozygote; D006706:Homeostasis; D006720:Homozygote; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism*; D009924:Organ Culture Techniques; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics* / Q000502:physiology; D017180:Tachycardia, Ventricular / Q000235:genetics* / Q000378:metabolism
D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium