Kimura Y, Inui M, Kadoma M, Kijima Y, Sasaki T, Tada M
First Department of Medicine, Osaka University School of Medicine, Japan.
J Mol Cell Cardiol. 1991 Nov;23(11):1223-30. doi: 10.1016/0022-2828(91)90080-6.
A monoclonal antibody against phospholamban has been reported to increase Ca2+ uptake by cardiac sarcoplasmic reticulum. We compared the effect of this antibody on Ca2+ pump ATPase activity of cardiac sarcoplasmic reticulum vesicles to the effect of cAMP-dependent phosphorylation of phospholamban. The antibody markedly stimulated the Ca(2+)-dependent ATPase activity in parallel to the increase in Ca2+ uptake by cardiac sarcoplasmic reticulum. When the Ca(2+)-dependent profile of the ATPase activity was compared, the KCa was shifted from 1.24 to 0.62 microM by the antibody, whereas cAMP-dependent phosphorylation of phospholamban shifted the KCa to 0.84 microM. When cardiac sarcoplasmic reticulum vesicles were treated with both cAMP-dependent protein kinase and the antibody, the stimulation was the same as that with the antibody alone. Thus, the Ca2+ pump ATPase seems to be fully activated by the antibody. The stoichiometry between Ca2+ uptake and ATPase rate was around 1 and no significant change was observed by the treatment with the antibody. Therefore, the stimulation of Ca2+ uptake of cardiac sarcoplasmic reticulum by the antibody occurred by the stimulation of Ca2+ pump ATPase, not by other mechanisms such as channel activity of phospholamban. These results indicate that the binding of the antibody to phospholamban produces essentially the same mode of action on Ca2+ pump ATPase as that of phospholamban phosphorylation. The antibody and phospholamban phosphorylation appear to release the inhibitory action of phospholamban on Ca2+ pump ATPase, resulting in the stimulation of Ca2+ pump.
据报道，一种抗受磷蛋白的单克隆抗体可增加心肌肌浆网对钙离子的摄取。我们将这种抗体对心肌肌浆网囊泡钙离子泵ATP酶活性的影响与受磷蛋白的cAMP依赖性磷酸化作用的影响进行了比较。该抗体显著刺激了钙离子依赖性ATP酶活性，这与心肌肌浆网对钙离子摄取的增加是平行的。当比较ATP酶活性的钙离子依赖性曲线时，该抗体使钙离子半最大激活浓度（KCa）从1.24微摩尔/升变为0.62微摩尔/升，而受磷蛋白的cAMP依赖性磷酸化则使KCa变为0.84微摩尔/升。当用cAMP依赖性蛋白激酶和该抗体同时处理心肌肌浆网囊泡时，刺激作用与单独使用该抗体时相同。因此，钙离子泵ATP酶似乎被该抗体完全激活。钙离子摄取与ATP酶速率之间的化学计量比约为1，用该抗体处理后未观察到显著变化。所以，该抗体对心肌肌浆网钙离子摄取的刺激是通过刺激钙离子泵ATP酶实现的，而非通过其他机制，如受磷蛋白的通道活性。这些结果表明，抗体与受磷蛋白的结合对钙离子泵ATP酶产生的作用模式与受磷蛋白磷酸化基本相同。抗体和受磷蛋白磷酸化似乎解除了受磷蛋白对钙离子泵ATP酶的抑制作用，从而导致钙离子泵的激活。
