Abstract 9709: CaMKII-mediated Aberrant Ca2+ Release May Play a Key Role in hte Arrhythmogenesis In Cardiac Troponin T-related Familial Hypertrophic Cardiomyopathy
Backgrounds: Cardiac troponin T (cTnT) mutations causes Familial Hypertrophic Cardiomyopathy (FHC), which leads to sudden cardiac death. In many of the non-dilated forms of FHC-linked cTnT mutations, Ca2+ sensitivity in myofilament is increased. However, the underlying mechanism by which the cTnT mutations leads to lethal arrhythmia remains elusive. Here, we hypothesized that aberrant Ca2+ release via the cardiac ryanodine receptor (RyR2) would occur in FHC. To verify this hypothesis, we investigated local Ca2+ release property in transgenic (TG) mouse model with FHC-related cTnT mutation (delta160E).
Methods and results: In the TG mouse model, there was no appreciable difference in the structural or functional features of the hearts between wild-type (WT) and TG mice in 6th month of age. In response to isoproterenol (ISO; 10 nmol/L), the Ca2+ spark frequency (SpF: s-1•100µm-1; by fluo4) was much higher in TG cardiomyocytes than in WT cardiomyocytes TG (n=10): 7.8±0.9; WT (n=5): 3.6±0.4; p<0.01. It was largely reversed by CaMKII inhibitor (KN-93 ;1 µM), TG with KN-93(n=5: 5.0±0.3; p<0.05), but not by PKA inhibitor (H-89; 1 µM), TG with H-89(n=5: 7.6±0.3; n.s). In ISO-treated TG cardiomyocytes, time from peak to 70% decline of Ca2+ transient was attenuated by KN-93 (1 µM, n=5: 6.44±0.35 x10-2sec; p<0.05 vs ISO-treated TG (n=5: 7.61±0.18 x10-2sec;), but not by H-89 (1 µM, n=5: 6.88±1.15 x10-2sec; n.s.). ISO-treated TG cardiomyocytes (but not ISO-treated WT: 0/14; n=14) showed spontaneous Ca2+ transient (sCaT) after 5 Hz pacing (12/18; n=13). The spontaneous Ca2+ transient was again attenuated by KN-93 (0/5; n=5), but not by H-89 (3/5; n=5). Moreover, all of these abnormal events in ISO-treated TG cardiomyocytes (i.e. increase in SpF and appearance of sCaT) were reproduced by adding EGTA-AM into ISO-treated WT cardiomyocytes, suggesting that increased Ca2+ buffering capacity, causing an increase in diastolic [Ca2+], predisposes to aberrant Ca2+ release events.
Conclusions: In FHC-linked cTnT mutated hearts aberrant local Ca2+ release is induced by beta-adrenergic stimulation, presumably due to mutation-linked, increased Ca2+ buffering capacity, and subsequent CaMKII activation.
- © 2012 by American Heart Association, Inc.