cMyBP-C Phosphorylated Mimetic (t3SD) Preserves Myocardial Relaxation With Aging Independently of [Ca2+]i Kinetics
Force and intracellular calcium [Ca2+]i were simultaneously measured on intact papillary muscles from mouse models 12 to 15 months old with increasing pacing frequency (1.0 to 2.0 Hz). (A to C) cMyBP-C(t3SD) showed greater acceleration of relaxation in response to increased pacing frequency with increasing magnitude of dFR, dFR = [(–dF/dt)min/(+dF/dt)max]. (D to F) Normalized [Ca2+]i traces show that increasing pacing frequency shortens [Ca2+]i decay times in a similar manner for all models. (G) Increased pacing frequency causes faster relaxation in the cMyBP-C(t3SD) aged model. (H) Increasing pacing frequency causes similar increases in the [Ca2+]i decay rate constant (kCa) in all mouse models. Repeated measure analysis of variance with intergroup comparison was used to identify significant differences in responses to increasing pacing frequency on intact papillary muscles among the 3 strains.