Altered cardiac excitation–contraction coupling in mutant mice with familial hypertrophic cardiomyopathy

Abstract

Familial hypertrophic cardiomyopathy (FHC) is an inherited autosomal dominant disease characterized by ventricular hypertrophy and myofibrillar disarray. Sudden cardiac death, especially among young athletes, represents the most severe outcome of FHC in affected individuals (1-3). The genetic alterations have been localized to genes that encode various myofibrillar proteins (4,5). Among these, the β-myosin heavy chain (β-MHC) gene was the first to be implicated and remains the most common identified cause of FHC. Recently, a transgenic model of FHC in mice with truncated troponin T (TnT) has also been developed (6). These transgenic mice hearts are smaller than wild-type, with fewer myocytes, but they exhibit significant delay in relaxation in response to increased work load with mild systolic dysfunction. Despite these advances, it is not yet clear how the genetic lesions produce the characteristic phenotype.Few studies have attempted to investigate the functional abnormalities of hypertrophic cardiac muscles of FHC. Lin et al. (7) showed increased motility of thin filaments containing mutant TnT (TnT I91N), a lesion associated with FHC. Similarly, myotubes with truncated TnT (also implicated in FHC) produced less force (8). Mutated myosin molecules also demonstrated decreased actin translocating activity (9). Nevertheless, direct evidence of altered function in intact myocardium is sparse, and little is known about the pathophysiology of excitation-contraction coupling in FHC.The recent introduction of an FHC mutation (Arg403Gln) into the mouse α-MHC gene has produced an animal model resembling, in many aspects, human FHC (10). Here, we have studied the physiological properties of muscles from the hearts of these mice. The results indicate that there are alterations in excitation-contraction coupling in mutant mice, with lesions in myofilament contraction and associated changes of intracellular Ca 2+ ([Ca 2+ ] i ) handling. MethodsMouse muscle preparation. Adult male mice (Black Swiss strain, ∼20 weeks old, ∼35 g; for a detailed description of the mouse model of FHC, see ref. 10) were anesthetized by intra-abdominal injection of sodium pentobarbital (∼10-20 mg), and the hearts were rapidly excised via midsternal thoracotomy. As described for wild-type mice of another strain (11), the hearts were retrogradely perfused with modified Krebs-Henseleit (KH) buffer with high K + (20 mM) and gassed with a 95% O 2 /5% CO 2 gas mixture in a dissection dish at room temperature. Trabeculae or small papillary muscles (in mm: wild-type 0.90 ± 0.34 long, 0.18 ± 0.08 wide, and 0.11 ± 0.05 thick, n = 8; mutant 0.70 ± 0.21 long, 0.21 ± 0.10 wide, and 0.12 ± 0.04 thick, n = 8; mean ± SD) were quickly dissected from the right ventricle and mounted between a force transducer and a micromanipulator in a perfusion bath. The muscles were superfused with KH buffer equilibrated with 95% O 2 /5% CO 2 . The KH buffer was composed of (in mM): 142 Na + , 5 K + , 1.2 Mg 2+ , 127.4 Cl -, 2 PO 4 -, 20 HCO 3 -, 1.0 CaCl 2 (pH 7.35-7.4). The ...

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“…In addition, cardiomyocytes from these transgenic animals showed a reduced rate of decline of intracellular Ca 2+ in comparison with wild-type mice [70]. Gao et al [71] also reported that mutant myofilaments were more sensitive to Ca 2+ and that this resulted in diastolic dysfunction, a result also discovered in a beta-myosin heavy chain-Q403 transgenic rabbit [72]. Intracellular Ca 2+ was also a factor in a dog model of arrhythmogenic right ventricular cardiomyopathy with a spontaneous mutation in calstabin 2.…”

Chronic Treatment With Allopurinol Boosts Survival and Cardiac Contractility in Murine Postischemic Cardiomyopathy

“…6,14,15 Briefly, muscles were stimulated at 14 Hz at increasing concentrations of [Ca 2ϩ ] o , usually 1 to 20 mmol/L for 5 to 10 seconds until force reached a plateau. [Ca 2ϩ ] i was measured simultaneously with force and calculated as described.…”

Allele-specific differences in transcriptome, miRNome, and mitochondrial function in two hypertrophic cardiomyopathy mouse models

“…Two genetic mouse models of HCM that have been well characterized (8,9,13,18,(32)(33)(34), namely the R403Q mutation in the α-myosin heavy chain gene (αMy-HC; MYH6 gene) (33) and the R92W mutation in the cardiac troponin T gene (TnT; TNNT2 gene) (34), serve as the platform for our comparative studies. Both mutations increase tension cost and lead to energetic stress under high workloads (13,18).…”