Pentameric assembly of phospholamban facilitates inhibition of cardiac function in vivo
Pentameric assembly of phospholamban facilitates inhibition of cardiac function in vivo
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DOI：
10.1074/jbc.273.50.33674
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发表时间：
1998-12-11
影响因子：
4.8
通讯作者：
Kranias, EG
中科院分区：
文献类型：
--
作者：
Chu, GX;Li, L;Kranias, EG
磷蛋白被认为在天然肌浆网膜中以五聚体和单体共存。为了确定其在体内的功能单位，我们在磷蛋白敲除小鼠的心脏中重新引入了野生型（五聚体）或单体突变型（C41F）磷蛋白。鉴定了表达相似水平的突变型或野生型磷蛋白的转基因系，并对其心脏表型进行了相似的表征。肌浆网Ca2+转运试验表明，突变型或野生型磷蛋白对SERCA2 Ca2+亲和力的降低相似。然而，野生型磷蛋白比突变型磷蛋白更大程度地降低了分离心肌细胞的松弛时间常数和Ca2+瞬态下降，即使两组之间心肌细胞收缩和Ca2+瞬态的幅度没有显著差异。Langendorff灌注还表明，突变型磷蛋白不能像野生型磷蛋白那样抑制磷蛋白敲除心脏的增强松弛参数。此外，小鼠体内血流动力学评估显示，野生型比突变型磷蛋白对心脏功能的抑制更大。因此，突变型或单体形式的磷蛋白在减缓心肌细胞、心脏或完整动物的Ca2+下降或松弛方面不如野生型或五聚体磷蛋白有效。这些发现表明，磷蛋白的五聚体组装是体内心肌收缩性的最佳调节所必需的。
Phospholamban has been proposed to coexist as pentamers and monomers in native sarcoplasmic reticulum membranes. To determine its functional unit in vivo, we reintroduced wild-type (pentameric) or monomeric mutant (C41F) phospholamban in the hearts of phospholamban knockout mice. Transgenic lines, expressing similar levels of mutant or wild-type phospholamban, were identified, and their cardiac phenotypes were characterized in parallel. Sarcoplasmic reticulum Ca2+ transport assays indicated similar decreases in SERCA2 Ca2+ affinity by mutant or wild-type phospholamban, However, the time constants of relaxation and Ca2+ transient decline in isolated cardiomyocytes were diminished to a greater extent by wild-type than mutant phospholamban, even without significant differences in the amplitudes of myocyte contraction and Ca2+ transients between the two groups. Langendorff perfusion also indicated that mutant phospholamban was not capable of depressing the enhanced relaxation parameters of the phospholamban knockout hearts to the same extent as wild-type phospholamban, Moreover, in vivo assessment of mouse hemodynamics revealed a greater depression of cardiac function in wild-type than mutant phospholamban hearts. Thus, the mutant or monomeric form of phospholamban was not as effective in slowing Ca2+ decline or relaxation in cardiomyocytes, hearts, or intact animals as wild-type or pentameric phospholamban. These findings suggest that pentameric assembly of phospholamban is necessary for optimal regulation of myocardial contractility in vivo.