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.

Inhibition of renin-angiotensin system (RAS) reduces ventricular tachycardia risk by altering connexin43.

Renin-angiotensin system (RAS) activation is associated with arrhythmias. We investigated the effects of RAS inhibition in cardiac-specific angiotensin-converting enzyme (ACE) overexpression (ACE 8/8) mice, which exhibit proclivity to ventricular tachycardia (VT) and sudden death because of reduced connexin43 (Cx43). ACE 8/8 mice were treated with an ACE inhibitor (captopril) or an angiotensin receptor type-1 blocker (losartan). Subsequently, electrophysiological studies were performed, and the hearts were extracted for Cx43 quantification using immunoblotting, immunohistochemistry, fluorescent dye spread method, and sodium current quantification using whole cell patch clamping. VT was induced in 12.5% of captopril-treated ACE 8/8 and in 28.6% of losartan-treated mice compared to 87.5% of untreated mice (P < 0.01). Losartan and captopril treatment increased total Cx43 2.4-fold (P = 0.01) and the Cx43 phosphorylation ratio 2.3-fold (P = 0.005). Treatment was associated with a recovery of gap junctional conductance. Survival in treated mice improved to 0.78 at 10 weeks (95% confidence interval 0.64 to 0.92), compared to the expected survival of less than 0.50. In a model of RAS activation, arrhythmic risk was correlated with reduced Cx43 amount and phosphorylation. RAS inhibition resulted in increased total and phosphorylated Cx43, decreased VT inducibility, and improved survival.

The relationship between ventricular repolarization duration and RR interval in normal subjects and patients with myocardial infarction.

OBJECTIVES: When either ventricular myocardium becomes ischemic or autonomic nervous system activity changes with age, the relationship between ventricular repolarization duration and RR interval will change as well. We studied the relationship between ventricular repolarization duration and RR interval among normal subjects in different age groups and between patients with myocardial infarction (MI) and age-matched healthy subjects. METHODS: Ventricular repolarization duration variability (RDV) spectra were separated into RR-dependent and RR-independent components. We compared spectral measures among normal subjects in different age groups and between patients with MI and age-matched healthy subjects. RESULTS: The RR-dependent component of RDV spectra, which is correlated with autonomic nervous system activity, significantly decreased with age for healthy subjects. The RR-independent component significantly increased in MI patients compared to age-matched healthy subjects. CONCLUSIONS: We demonstrated the increase in RDV upon decreasing age and in the presence of MI. Our results support the idea that the RR-dependent part corresponds to the physiology-related part of the RDV spectra and the RR-independent part corresponds to the pathology-related part of the RDV spectra. Our study suggests that these spectral measures are likely to be helpful in the evaluation of a patient with MI and merit further investigation.

The voltage dependence of recovery from use-dependent block by QX-222 separates mechanisms for drug egress in the cardiac sodium channel.

In neuronal sodium channels of squid giant axons, recovery from QX-222 block is slowed by hyperpolarization. However, in ventricular cells, hyperpolarization speeds recovery. Previously, we showed that isoform-specific residues in the external side of the cardiac sodium channel isoform (D1P-loop C373 and D4S6 T1752) influence use-dependent block (UDB) by lidocaine. To determine whether these isoformspecific residues contribute to the contrasting voltage-dependent recovery observed in ventricular myocytes, we measured recovery rates from UDB by QX-222 at holding potentials of 120, 140, 160 and 180 mV for wild-type cardiac channel (WT), the mutants C373Y (CY) and T1752V (TV), and C373Y/T1752V (CY/TV). Unlike neuronal channels, cardiac sodium channels recovered from QX block faster at hyperpolarized potentials. All mutations slowed QX-222 recovery, with the greatest rate reduction observed for the double mutant, indicating that the isoform-specific residues define external drug paths. The recovery rates varied linearly with voltage over the range tested, and we used the slopes of rate versus voltage plots to quantify voltage dependence. The TV mutation caused reduction in recovery rates without changing the slope, indicating that the mutation closed a voltage-independent egress path. The CY mutation, however, flattened the slope and reduced the voltage dependence of recovery. In addition, the reduction in rate caused by CY/TV is less than the sum of those for CY and TV, suggesting that the impacts of these two residues are interrelated. Therefore, we propose that the isoform-specific residues C373 and T1752 change recovery from UDB by distinct mechanisms but determine a common drug egress path.

Is the 1,3,5-tridehydrobenzene triradical a cyclopropenyl radical analogue?

The gas-phase heat of formation (DeltaH(f,298)) of the 1,3,5-tridehydrobenzene triradical has been determined by using a negative ion thermochemical cycle. The first three measurements carried out were of the gas-phase acidity of 3,5-dichlorobenzoic acid, the enthalpy for decarboxylation of 3,5-dichlorobenzoate, and the enthalpy for chloride loss from 3,5,-dichlorophenide and constitute the measurement of the heat of formation for 5-chloro-m-benzyne. The last two measurements, the electron affinity of 5-chloro-m-benzyne, and the threshold for chloride loss from 5-chloro-m-benzyne, when combined with DeltaH(f,298) of 5-chloro-m-benzyne, give the heat of formation of the triradical. The 5-chloro-m-benzyne heat of formation is 116.2 +/- 3.7 kcal/mol. The heat of formation of the 1,3,5-tridehydrobenzene triradical measured in this work is 179.1 +/- 4.6 kcal/mol. This heat of formation was used to derive the bond dissociation energy (BDE) at the 5-position of m-benzyne, a third BDE in benzene. The BDE, at 109.2 +/- 5.6 kcal/mol, is ca. 4 kcal/mol lower than the first BDE in benzene (112.9 kcal/mol) and significantly higher than the BDE of phenyl radical at the meta position. The agreement between the first and third BDEs implies that the triradical is best described as a phenyl radical that interacts little with a m-benzyne moiety. The experimentally measured BDE is in good agreement with multireference configuration interaction calculations, which predict a (2)A(1) ground state for the Jahn-Teller distorted triradical. The trends in the first, second, and third BDEs of benzene are similar to those found for cyclopropane, suggesting a cyclopropenyl-like electronic structure within the six-membered ring of the 1,3,5-benzene triradical.