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Background  Manganese-enhanced cardiovascular magnetic resonance (MECMR) can non-invasively assess myocardial calcium influx, and calcium levels are known to be elevated in muscular dystrophy cardiomyopathy based on cellular studies.    Methods  Left ventricular functional studies and MECMR were performed in  mdx  mice (model of Duchenne Muscular Dystrophy, 24 and 40 weeks) and  Sgcd−/−  mice (Limb Girdle Muscular Dystrophy 2 F, 16 and 32 weeks), compared to wild type controls (C57Bl/10, WT).    Results  Both models had left ventricular hypertrophy at the later age compared to WT, though the  mdx  mice had reduced stroke volumes and the  Sgcd−/−  mice increased heart rate and cardiac index. Especially at the younger ages, MECMR was significantly elevated in both models (both  P <0.05 versus WT). The L-type calcium channel inhibitor diltiazem (5 mg/kg i.p.) significantly reduced MECMR in the  mdx  mice ( P <0.01), though only with a higher dose (10 mg/kg i.p.) in the  Sgcd−/−  mice ( P <0.05). As the  Sgcd−/−  mice had increased heart rates, to determine the role of heart rate in MECMR we studied the hyperpolarization-activated cyclic nucleotide-gated channel inhibitor ZD 7288 which selectively reduces heart rate. This reduced heart rate and MECMR in all mouse groups. However, when looking at the time course of reduction of MECMR in the  Sgcd−/−  mice at up to 5 minutes of the manganese infusion when heart rates were matched to the WT mice, MECMR was still significantly elevated in the  Sgcd−/−  mice ( P <0.01) indicating that heart rate alone could not account for all the increased MECMR.    Conclusions  Despite both mouse models exhibiting increased  in-vivo  calcium influx at an early stage in the development of the cardiomyopathy before left ventricular hypertrophy, there are distinct phenotypical differences between the 2 models in terms of heart rates, hemodynamics and responses to calcium channel inhibitors.

Heterogeneous abnormalities of in-vivo left ventricular calcium influx and function in mouse models of muscular dystrophy cardiomyopathy