Cardiac Hypertrophy Associated with Impaired Regulation of Type2 Ryanodine Receptor Calcium Channel by Calmodulin and S100A1

Abstract

The cardiac ryanodine receptor ion channel (RyR2) is inhibited in vitro by calmodulin (CaM). Simultaneous substitution of three amino acid residues in the CaM binding domain (W3587A/L3591D/F3603A, RyR2ADA) leads to loss of CaM inhibition at submicromolar (diastolic) and micromolar (systolic) Ca2+ concentrations in vitro and cardiac hypertrophy and heart failure in mice. To address whether elimination of CaM inhibition at diastolic or systolic Ca2+ causes cardiac hypertrophy, a second mutant mouse was prepared with a single amino acid substitution (L3591D, RyR2D) in the CaM binding domain. In single channel measurements, RyR2D lost CaM inhibition at diastolic but not systolic Ca2+, and lost inhibition by the small Ca2+ binding protein S100A1 at both diastolic and systolic Ca2+. In contrast to Ryr2ADA/ADA mice, Ryr2D/D mice had a normal lifespan and cardiac contractility. In 6-month old Ryr2D/D mice, heart-to-body weight ratio increased by 8% with a two-fold upregulation of atrial natriuretic peptide mRNA levels and a 40% decrease in RyR2 content. Differences between mutant and wild-type mice were more prominent in mice subjected to 4 weeks pressure overload using transverse aortic constriction. The results contrast those of Ryr2ADA/ADA mice that have an impaired cardiac contractile performance and die at ∼2 weeks after birth, and suggest that CaM inhibition of RyR2 at systolic Ca2+ is important for maintaining normal cardiac function. Supported by NIH, AHA and NSF.