Background-The development of heart failure is tightly correlated with a decrease in the stoichiometric ratio for FKBP12.6 binding to the ryanodine receptor (RyR) in the sarcoplasmic reticulum (SR). We report that a new drug, the 1,4-benzothiazepine derivative JTV519, reverses this pathogenic process. JTV519 is known to have a protective effect against Ca 2ϩ overload-induced myocardial injury. Methods and Results-Heart failure was produced by 4 weeks of rapid right ventricular pacing, with or without JTV519; SR were then isolated from dog left ventricular (LV) muscles. First, in JTV519-treated dogs, no signs of heart failure were observed after 4 weeks of chronic right ventricular pacing, LV systolic and diastolic functions were largely preserved, and LV remodeling was prevented. Second, JTV519 acutely inhibited both the FK506-induced Ca 2ϩ leak from RyR in normal SR and the spontaneous Ca 2ϩ leak in failing SR. Third, there was no abnormal Ca 2ϩ leak in SR vesicles isolated from JTV519-treated hearts. Fourth, in JTV519-treated hearts, both the stoichiometry of FKBP12.6 binding to RyR and the amount of RyR-bound FKBP12.6 were restored toward the values seen in normal SR. Fifth, in JTV519-untreated hearts, RyR was PKA-hyperphosphorylated, whereas it was reversed in JTV519-treated hearts, returning the channel phosphorylation toward the levels seen in normal hearts. Conclusions-During the development of experimental heart failure, JTV519 prevented the amount of RyR-bound FKBP12.6 from decreasing. This in turn reduced the abnormal Ca 2ϩ leak through the RyR, prevented LV remodeling, and led to less severe heart failure.

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We have recently shown that RyR2 (cardiac ryanodine receptor) is phosphorylated by PKA (protein kinase A/cAMP-dependent protein kinase) at two major sites, Ser-2030 and Ser-2808. In the present study, we examined the properties and physiological relevance of phosphorylation of these two sites. Using site- and phospho-specific antibodies, we demonstrated that Ser-2030 of both recombinant and native RyR2 from a number of species was phosphorylated by PKA, indicating that Ser-2030 is a highly conserved PKA site. Furthermore, we found that the phosphorylation of Ser-2030 responded to isoproterenol (isoprenaline) stimulation in rat cardiac myocytes in a concentration- and time-dependent manner, whereas Ser-2808 was already substantially phosphorylated before beta-adrenergic stimulation, and the extent of the increase in Ser-2808 phosphorylation after beta-adrenergic stimulation was much less than that for Ser-2030. Interestingly, the isoproterenol-induced phosphorylation of Ser-2030, but not of Ser-2808, was markedly inhibited by PKI, a specific inhibitor of PKA. The basal phosphorylation of Ser-2808 was also insensitive to PKA inhibition. Moreover, Ser-2808, but not Ser-2030, was stoichiometrically phosphorylated by PKG (protein kinase G). In addition, we found no significant phosphorylation of RyR2 at the Ser-2030 PKA site in failing rat hearts. Importantly, isoproterenol stimulation markedly increased the phosphorylation of Ser-2030, but not of Ser-2808, in failing rat hearts. Taken together, these observations indicate that Ser-2030, but not Ser-2808, is the major PKA phosphorylation site in RyR2 responding to PKA activation upon beta-adrenergic stimulation in both normal and failing hearts, and that RyR2 is not hyperphosphorylated by PKA in heart failure. Our results also suggest that phosphorylation of RyR2 at Ser-2030 may be an important event associated with altered Ca2+ handling and cardiac arrhythmia that is commonly observed in heart failure upon beta-adrenergic stimulation.

The sustained early systolic loading due to the increase in characteristic impedance was accompanied by less concentric, reduced hypertrophy, whereas the sustained late systolic loading due to the augmented arterial wave reflection was accompanied by concentric, adequate hypertrophy.

The causes of reduced cardiac force development in congestive heart failure (CHF) are still uncertain. We explored the subcellular mechanisms leading to decreased force development in trabeculae from rats with a myocardial infarction. We defined CHF according to clinical and pathological criteria and compared properties of trabeculae from animals with CHF (cMI) to those of animals with a myocardial scar but without evidence of CHF (uMI), and sham-operated animals. The new findings of this study on properties of cMI trabeculae are that (1) maximal twitch force following post-extrasystolic potentiation is unchanged; (2) the sensitivity of cMI trabeculae to [Ca(2+)](o) is increased; (3) spontaneous diastolic sarcomere length (SL) fluctuations (SA) are increased in cMI at all levels of SR Ca(2+) loading; and (4) SA is accompanied by a proportional reduction of F(max). The results suggest that the probability of spontaneous diastolic opening of SR Ca(2+) channels is increased in CHF. These data provide the basis for a novel mechanism underlying systolic and diastolic dysfunction as well as arrhythmias in hearts in CHF. If SA proves to be a component of myocardial dysfunction in human CHF, our thinking about therapy of the patient with CHF may be profoundly changed.