Ranolazine improves cardiac diastolic dysfunction through modulation of myofilament calcium sensitivity

Rationale: Previously, we demonstrated that a deoxycorticosterone acetate (DOCA)-salt hypertensive mouse model produces cardiac oxidative stress and diastolic dysfunction with preserved systolic function. Oxidative stress has been shown to increase late inward sodium current (I _Na), reducing the net cytosolic Ca ²⁺ efflux. Objective: Oxidative stress in the DOCA-salt model may increase late I _Na, resulting in diastolic dysfunction amenable to treatment with ranolazine. Methods and Results: Echocardiography detected evidence of diastolic dysfunction in hypertensive mice that improved after treatment with ranolazine (E/E′:sham, 31.9±2.8, sham+ranolazine, 30.2±1.9, DOCA-salt, 41.8±2.6, and DOCA-salt+ranolazine, 31.9±2.6; P=0.018). The end-diastolic pressure-volume relationship slope was elevated in DOCA-salt mice, improving to sham levels with treatment (sham, 0.16±0.01 versus sham+ranolazine, 0.18±0.01 versus DOCA-salt, 0.23±0.2 versus DOCA-salt+ranolazine, 0.17±0.0 1 mm Hg/L; P<0.005). DOCA-salt myocytes demonstrated impaired relaxation, τ, improving with ranolazine (DOCA-salt, 0.18±0.02, DOCA-salt+ranolazine, 0.13±0.01, sham, 0.11±0.01, sham+ranolazine, 0.09±0.02 seconds; P=0.0004). Neither late I _Na nor the Ca ²⁺ transients were different from sham myocytes. Detergent extracted fiber bundles from DOCA-salt hearts demonstrated increased myofilament response to Ca ²⁺ with glutathionylation of myosin binding protein C. Treatment with ranolazine ameliorated the Ca ²⁺ response and cross-bridge kinetics. Conclusions: Diastolic dysfunction could be reversed by ranolazine, probably resulting from a direct effect on myofilaments, indicating that cardiac oxidative stress may mediate diastolic dysfunction through altering the contractile apparatus.