Belevych Andriy E, Ho Hsiang-Ting, Bonilla Ingrid M, Terentyeva Radmila, Schober Karsten E, Terentyev Dmitry, Carnes Cynthia A, Györke Sándor
Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, 43210, USA.
Davis Heart and Lung Research Institute, The Ohio State University Medical Center, Columbus, OH, 43210, USA.
Basic Res Cardiol. 2017 Jul;112(4):44. doi: 10.1007/s00395-017-0633-2. Epub 2017 Jun 13.
In heart failure (HF), dysregulated cardiac ryanodine receptors (RyR2) contribute to the generation of diastolic Ca waves (DCWs), thereby predisposing adrenergically stressed failing hearts to life-threatening arrhythmias. However, the specific cellular, subcellular, and molecular defects that account for cardiac arrhythmia in HF remain to be elucidated. Patch-clamp techniques and confocal Ca imaging were applied to study spatially defined Ca handling in ventricular myocytes isolated from normal (control) and failing canine hearts. Based on their activation time upon electrical stimulation, Ca release sites were categorized as coupled, located in close proximity to the sarcolemmal Ca channels, and uncoupled, the Ca channel-free non-junctional Ca release units. In control myocytes, stimulation of β-adrenergic receptors with isoproterenol (Iso) resulted in a preferential increase in Ca spark rate at uncoupled sites. This site-specific effect of Iso was eliminated by the phosphatase inhibitor okadaic acid, which caused similar facilitation of Ca sparks at coupled and uncoupled sites. Iso-challenged HF myocytes exhibited increased predisposition to DCWs compared to control myocytes. In addition, the overall frequency of Ca sparks was increased in HF cells due to preferential stimulation of coupled sites. Furthermore, coupled sites exhibited accelerated recovery from functional refractoriness in HF myocytes compared to control myocytes. Spatially resolved subcellular Ca mapping revealed that DCWs predominantly originated from coupled sites. Inhibition of CaMKII suppressed DCWs and prevented preferential stimulation of coupled sites in Iso-challenged HF myocytes. These results suggest that CaMKII- (and phosphatase)-dependent dysregulation of junctional Ca release sites contributes to Ca-dependent arrhythmogenesis in HF.
在心力衰竭（HF）中，心肌兰尼碱受体（RyR2）调节异常会导致舒张期钙波（DCW）的产生，从而使承受肾上腺素能应激的衰竭心脏易发生危及生命的心律失常。然而，导致HF中心律失常的具体细胞、亚细胞和分子缺陷仍有待阐明。应用膜片钳技术和共聚焦钙成像来研究从正常（对照）和衰竭犬心脏分离的心室肌细胞中空间限定的钙处理情况。根据电刺激后的激活时间，钙释放位点被分类为耦联位点（位于肌膜钙通道附近）和解耦联位点（无钙通道的非连接性钙释放单元）。在对照心肌细胞中，用异丙肾上腺素（Iso）刺激β-肾上腺素能受体会导致解耦联位点处的钙火花发生率优先增加。Iso的这种位点特异性作用被磷酸酶抑制剂冈田酸消除，冈田酸会导致耦联位点和解耦联位点处的钙火花出现类似的促进作用。与对照心肌细胞相比，Iso刺激的HF心肌细胞发生DCW的倾向增加。此外，由于耦联位点受到优先刺激，HF细胞中钙火花的总体频率增加。此外，与对照心肌细胞相比，HF心肌细胞中的耦联位点从功能不应期恢复的速度加快。空间分辨亚细胞钙图谱显示，DCW主要起源于耦联位点。抑制钙/钙调蛋白依赖性蛋白激酶II（CaMKII）可抑制DCW，并防止Iso刺激的HF心肌细胞中耦联位点受到优先刺激。这些结果表明，连接性钙释放位点的CaMKII（和磷酸酶）依赖性调节异常促成了HF中钙依赖性心律失常的发生。
