Increased phospholamban phosphorylation limits the force–frequency response in the MLP^–/– mouse with heart failure

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• 作者：Gudrun Antoons ; Peter Vangheluwe ; Paul G.A. Volders ; Virginie Bito ; Patricia Holemans ; Marcello Ceci ; Frank Wuytack ; Pico Caroni ; Kanigula Mubagwa and Karin R. Sipido
• 关键词：Heart failure ; Sarcoplasmic reticulum ; Phospholamban ; Frequency response
• 刊名：Journal of Molecular and Cellular Cardiology
• 出版年：2006
• 出版时间：March 2006
• 年：2006
• 卷：40
• 期：3
• 页码：350-360
• 全文大小：690 K

文摘

Reduced Ca²⁺ 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 Ca²⁺ handling in MLP^–/– remain incompletely understood. We studied [Ca²⁺]_i in left ventricular myocytes from MLP^–/– and WT mice (3–4 months old; whole-cell voltage clamp, 30 °C). At 1 Hz stimulation, the amplitude of [Ca²⁺]_i transients was similar. However, in contrast to WT, at higher frequencies the [Ca²⁺]_i transient amplitude declined in MLP^–/– and there was no increase in SR Ca²⁺ content. Unexpectedly, the decline of [Ca²⁺]_i was faster in MLP^–/– than in WT (at 1 Hz, τ 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 Ca²⁺ affinity of SR Ca²⁺ 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 Ser¹⁶ and 2.9-fold at the Thr¹⁷ 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 Ca²⁺, suggesting inadequate Ca²⁺ sequestration in MLP^–/–. In conclusion, increased baseline phosphorylation of phospholamban in MLP^–/– leads to a reduced reserve for frequency-dependent increase of Ca²⁺ release. This represents a novel paradigm for altered Ca²⁺ handling in heart failure, underscoring the importance of phosphorylation pathways.