No abstract

Failing human myocardium has been associated with decreased sarcoplasmic reticulum (SR) Ca2+-ATPase activity. There remains controversy as to whether the regulation of SR Ca2+-ATPase activity is altered in heart failure or whether decreased SR Ca2+-ATPase activity is due to changes in SR Ca2+-ATPase or phospholamban expression. We therefore investigated whether alterations in cAMP-dependent phosphorylation of phospholamban may be responsible for the reduced SR Ca2+-ATPase activity in human heart failure. Protein levels of phospholamban and SR Ca2+-ATPase, detected by Western blot, were unchanged in failing compared with nonfailing human myocardium. There was decreased responsiveness to the direct activation of the SR Ca2+-ATPase activity by either cAMP (0.01–100 μmol/l) or protein kinase A (1–30 μg) in failing myocardium. Using the backphosphorylation technique, we observed a decrease of the cAMP-dependent phosphorylation level of phospholamban by 20 ± 2%. It is concluded that the impaired SR function in human end-stage heart failure may be due, in part, to a reduced cAMP-dependent phosphorylation of phospholamban.

Background-We investigated whether decreased myofilament calcium contractile activation may, in part, contribute to heart failure. Methods and Results-Calcium concentration required for 50% activation and Hill coefficient for fibers from nonfailing and failing human hearts at pH 7.1 were not different. Maximum calcium-activated force (F max ) was also not different. However, at pH 6.8 and 6.9, differences were seen in myofilament calcium activation between nonfailing and failing hearts. At lower pH, failing myocardium was shifted left on the calcium axis compared with nonfailing myocardium, which suggested an increase in myofilament calcium responsiveness. Increased inorganic phosphate concentration decreased maximal force development by 56% in nonfailing and 36% in failing myocardium and shifted the calcium-force relationship by 2.01Ϯ0.22 versus 0.86Ϯ0.13 mol/L, respectively (PϽ0.05). Addition of cAMP resulted in a 0.56 mol/L shift toward higher intracellular calcium concentrations in nonfailing myocardium and a 1.04 mol/L shift in failing myocardium. Protein kinase A in the presence of cAMP resulted in a further rightward shift in nonfailing human myocardium but did not further shift the calcium-force relationship in fibers from failing hearts. cGMP also resulted in a greater decrease in myofilament calcium sensitivity in fibers from failing hearts. Conclusions-We propose that changes at the level of the thin myofilaments result in differential responses to changes in the intracellular milieu in nonfailing versus failing myocardium.

Broad-breasted white turkey poults fed furazolidone developed dilated cardiomyopathy (DCM) characterized by ventricular dilatation, decreased ejection fraction, β1-receptor density, sarcoplasmic reticulum (SR) Ca2+-ATPase, myofibrillar ATPase activity, and reduced metabolism markers. We investigated the effects of carteolol, a β-adrenergic blocking agent, by administrating two different dosages (0.01 and 10.0 mg/kg) twice a day for 4 wk to control and DCM turkey poults. At completion of the study there was 59% mortality in the nontreated DCM group, 55% mortality in the group treated with the low dose of carteolol, and 22% mortality in the group treated with the high dose of carteolol. Both treated groups showed a significant decrease in left ventricle size and significant restoration of ejection fraction and left ventricular peak systolic pressure. Carteolol treatment increased β-adrenergic receptor density, and the high carteolol dose restored SR Ca2+-ATPase and myofibrillar ATPase activities, along with creatine kinase, lactate dehydrogenase, aspartate transaminase, and ATP synthase activities, to normal. These results show that β-blockade with carteolol improves survival, reverses contractile abnormalities, and induces cellular remodeling in this model of heart failure.