Author:

Keywords:

Animals, Calcium, Calcium Channels, L-Type, Calcium-Binding Proteins, Comparative Study, Electric Stimulation, Heart Diseases, Heart Ventricles, Mice, Mice, Knockout, Myocytes, Cardiac, Phosphorylation, Research Support, Non-U.S. Gov't, Sarcoplasmic Reticulum, Science & Technology, Life Sciences & Biomedicine, Cardiac & Cardiovascular Systems, Cell Biology, Cardiovascular System & Cardiology, heart failure, sarcoplasmic reticulum, phospholamban, frequency response, PROTEIN-KINASE-II, SARCOPLASMIC-RETICULUM CA2+, CHANNEL RYANODINE RECEPTOR, DILATED CARDIOMYOPATHY, VENTRICULAR MYOCYTES, CARDIAC-HYPERTROPHY, CALCIUM CONTENT, DOWN-REGULATION, RELEASE, EXPRESSION, 1102 Cardiorespiratory Medicine and Haematology, 1116 Medical Physiology, Cardiovascular System & Hematology, 3101 Biochemistry and cell biology, 3201 Cardiovascular medicine and haematology, 3208 Medical physiology

Abstract:

Reduced Ca(2+) release from the sarcoplasmic reticulum (SR) and a negative force-frequency relation characterize end-stage human heart failure. The MLP(-/-) mouse with dilated cardiomyopathy is used as a model to explore novel therapeutic interventions but the alterations in Ca(2+) handling in MLP(-/-) remain incompletely understood. We studied [Ca(2+)](i) in left ventricular myocytes from MLP(-/-) and WT mice (3-4 months old; whole-cell voltage clamp, 30 degrees C). At 1 Hz stimulation, the amplitude of [Ca(2+)](i) transients was similar. However, in contrast to WT, at higher frequencies the [Ca(2+)](i) transient amplitude declined in MLP(-/-) and there was no increase in SR Ca(2+) content. Unexpectedly, the decline of [Ca(2+)](i) was faster in MLP(-/-) than in WT (at 1 Hz, tau of 80 +/- 9 vs. 174 +/- 29 ms, P < / 0.001) and the frequency-dependent acceleration of the decline was abolished suggesting an enhanced basal SERCA activity. Indeed, the Ca(2+) affinity of SR Ca(2+) uptake in homogenates was higher in MLP(-/-), with the maximal uptake rate similar to WT. Phosphorylation of phospholamban in MLP(-/-) was increased (2.3-fold at Ser(16) and 2.9-fold at the Thr(17) site, P < / 0.001) with similar SERCA and total phospholamban protein levels. On increasing stimulation frequency to 4 Hz, WT, but not MLP(-/-), myocytes had a net gain of Ca(2+), suggesting inadequate Ca(2+) sequestration in MLP(-/-). In conclusion, increased baseline phosphorylation of phospholamban in MLP(-/-) leads to a reduced reserve for frequency-dependent increase of Ca(2+) release. This represents a novel paradigm for altered Ca(2+) handling in heart failure, underscoring the importance of phosphorylation pathways.