The RyR2-P2328S mutation downregulates Nav1.5 producing a ventricular arrhythmic substrate in murine ventricles.
Pflügers Archiv - European Journal of Physiology
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Ning, F., Luo, L., Ahmad, S., Valli, H., Jeevaratnam, K., Wang, T., Guzadhur, L., et al. (2015). The RyR2-P2328S mutation downregulates Nav1.5 producing a ventricular arrhythmic substrate in murine ventricles.. Pflügers Archiv - European Journal of Physiology, 468 655-665. https://doi.org/10.1007/s00424-015-1750-0
Catecholaminergic polymorphic ventricular tachycardia (CPVT) predisposes to ventricular arrhythmia due to altered Ca2+ homeostasis and can arise from ryanodine receptor (RyR2) mutations including RyR2-P2328S. Previous reports established that homozygotic murine RyR2-P2328S (RyR2S/S) hearts show an atrial arrhythmic phenotype associated with reduced action potential (AP) conduction velocity and sodium channel (Nav1.5) expression. We now relate ventricular arrhythmogenicity and slowed AP conduction in RyR2S/S hearts to connexin-43 (Cx43) and Nav1.5 expression, and Na+ current (INa). Stimulation protocols applying extrasystolic S2 stimulation following 8 Hz S1 pacing at progressively decremented S1S2 intervals confirmed an arrhythmic tendency despite unchanged ventricular effective refractory periods (VERPs) in Langendorff-perfused RyR2S/S hearts. Dynamic pacing imposing S1 stimuli then demonstrated that progressive reductions of basic cycle lengths (BCLs) produced greater reductions in conduction velocity at equivalent BCLs and diastolic intervals in RyR2S/S than WT, but comparable changes in AP durations (APD90) and their alternans. Western blot analyses demonstrated that Cx43 protein expression in whole ventricles were similar, but Nav1.5 expression in both whole tissue and membrane fractions were significantly reduced in RyR2S/S, compared to wild-type (WT). Loose patch-clamp studies similarly demonstrated reduced INa in RyR2S/S ventricles. We thus attribute arrhythmogenesis in RyR2S/S ventricles resulting from arrhythmic substrate produced by reduced conduction velocity to downregulated Nav1.5 reducing INa, despite normal determinants of repolarisation and passive conduction. The measured changes were quantitatively compatible with earlier predictions of linear relationships between conduction velocity and the peak INa of the AP but nonlinear relationships between peak INa and maximum Na+ permeability.
This work was supported by Royal Society / National Science Foundation of China International Joint Project Grant (JP100994/ No.81211130599) (JAF and AM), Issac Newton Trust/ Wellcome Trust ISSF/ University of Cambridge Joint Research Grants Scheme (JAF) and by the Wellcome Trust and Medical Research Council (CLH).
Royal Society (1562)
WELLCOME TRUST (105727/Z/14/Z)
British Heart Foundation (PG/14/79/31102)
External DOI: https://doi.org/10.1007/s00424-015-1750-0
This record's URL: https://www.repository.cam.ac.uk/handle/1810/252356
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Licence URL: http://creativecommons.org/licenses/by/4.0/