School of Physiology & Pharmacology, Centre for Nanoscience and Quantum Information, and Bristol Heart Institute, University of Bristol, Bristol, United Kingdom.
PLoS One. 2012;7(2):e31956. doi: 10.1371/journal.pone.0031956. Epub 2012 Feb 21.
Changes in FKBP12.6 binding to cardiac ryanodine receptors (RyR2) are implicated in mediating disturbances in Ca(2+)-homeostasis in heart failure but there is controversy over the functional effects of FKBP12.6 on RyR2 channel gating. We have therefore investigated the effects of FKBP12.6 and another structurally similar molecule, FKBP12, which is far more abundant in heart, on the gating of single sheep RyR2 channels incorporated into planar phospholipid bilayers and on spontaneous waves of Ca(2+)-induced Ca(2+)-release in rat isolated permeabilised cardiac cells. We demonstrate that FKBP12 is a high affinity activator of RyR2, sensitising the channel to cytosolic Ca(2+), whereas FKBP12.6 has very low efficacy, but can antagonise the effects of FKBP12. Mathematical modelling of the data shows the importance of the relative concentrations of FKBP12 and FKBP12.6 in determining RyR2 activity. Consistent with the single-channel results, physiological concentrations of FKBP12 (3 µM) increased Ca(2+)-wave frequency and decreased the SR Ca(2+)-content in cardiac cells. FKBP12.6, itself, had no effect on wave frequency but antagonised the effects of FKBP12.We provide a biophysical analysis of the mechanisms by which FK-binding proteins can regulate RyR2 single-channel gating. Our data indicate that FKBP12, in addition to FKBP12.6, may be important in regulating RyR2 function in the heart. In heart failure, it is possible that an alteration in the dual regulation of RyR2 by FKBP12 and FKBP12.6 may occur. This could contribute towards a higher RyR2 open probability, 'leaky' RyR2 channels and Ca(2+)-dependent arrhythmias.
FKBP12.6 与心脏兰尼碱受体 (RyR2) 的结合变化被认为介导心力衰竭时钙稳态的紊乱，但 FKBP12.6 对 RyR2 通道门控的功能影响存在争议。因此，我们研究了 FKBP12.6 和另一种结构上相似的分子 FKBP12（在心脏中更为丰富）对单个绵羊 RyR2 通道在平面磷脂双层中的门控以及在大鼠分离的通透化心脏细胞中自发的 Ca2+-诱导的 Ca2+释放波的影响。我们证明 FKBP12 是 RyR2 的高亲和力激活剂，使通道对细胞溶质 Ca2+敏感，而 FKBP12.6 则效力非常低，但可以拮抗 FKBP12 的作用。数据的数学建模表明 FKBP12 和 FKBP12.6 的相对浓度在确定 RyR2 活性方面的重要性。与单通道结果一致，生理浓度的 FKBP12（3 µM）增加了 Ca2+-波频率并降低了心脏细胞中的 SR Ca2+含量。FKBP12.6 本身对波频率没有影响，但拮抗了 FKBP12 的作用。我们提供了 FK 结合蛋白调节 RyR2 单通道门控的机制的生物物理分析。我们的数据表明，除了 FKBP12.6 之外，FKBP12 可能在调节心脏中的 RyR2 功能方面很重要。在心力衰竭中，FKBP12 和 FKBP12.6 对 RyR2 的双重调节可能发生改变。这可能导致 RyR2 开放概率更高、“渗漏” RyR2 通道和 Ca2+依赖性心律失常。
