Increased phospholamban phosphorylation limits the force-frequency response in the MLP-/- mouse with heart failure.
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.
Antoons
Gudrun
G
Laboratory of Experimental Cardiology, University of Leuven, Campus Gasthuisberg O/N 704, Herestraat 49, B-3000 Leuven, Belgium.
Vangheluwe
Peter
P
Volders
Paul G A
PG
Bito
Virginie
V
Holemans
Patricia
P
Ceci
Marcello
M
Wuytack
Frank
F
Caroni
Pico
P
Mubagwa
Kanigula
K
Sipido
Karin R
KR
D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D004558:Electric Stimulation; D006331:Heart Diseases / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000378:metabolism; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D000099211:Phospholamban
D002118:Calcium; D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; D000099211:Phospholamban