Wang Lianguo, Myles Rachel C, Lee I-Ju, Bers Donald M, Ripplinger Crystal M
Department of Pharmacology, School of Medicine, University of California, Davis, Davis, CA, United States.
Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom.
Front Physiol. 2021 May 11;12:656516. doi: 10.3389/fphys.2021.656516. eCollection 2021.
Sarcoplasmic reticulum (SR) Ca cycling is tightly regulated by ryanodine receptor (RyR) Ca release and sarco-endoplasmic reticulum Ca-ATPase (SERCA) Ca uptake during each excitation-contraction coupling cycle. We previously showed that RyR refractoriness plays a key role in the onset of SR Ca alternans in the intact rabbit heart, which contributes to arrhythmogenic action potential duration (APD) alternans. Recent studies have also implicated impaired SERCA function, a key feature of heart failure, in cardiac alternans and arrhythmias. However, the relationship between reduced SERCA function and SR Ca alternans is not well understood. Simultaneous optical mapping of transmembrane potential (V) and SR Ca was performed in isolated rabbit hearts ( = 10) using the voltage-sensitive dye RH237 and the low-affinity Ca indicator Fluo-5N-AM. Alternans was induced by rapid ventricular pacing. SERCA was inhibited with cyclopiazonic acid (CPA; 1-10 μM). SERCA inhibition (1, 5, and 10 μM of CPA) resulted in dose-dependent slowing of SR Ca reuptake, with the time constant () increasing from 70.8 ± 3.5 ms at baseline to 85.5 ± 6.6, 129.9 ± 20.7, and 271.3 ± 37.6 ms, respectively ( < 0.05 vs. baseline for all doses). At fast pacing frequencies, CPA significantly increased the magnitude of SR Ca and APD alternans, most strongly at 10 μM (pacing cycle length = 220 ms: SR Ca alternans magnitude: 57.1 ± 4.7 vs. 13.4 ± 8.9 AU; APD alternans magnitude 3.8 ± 1.9 vs. 0.2 ± 0.19 AU; < 0.05 10 μM of CPA vs. baseline for both). SERCA inhibition also promoted the emergence of spatially discordant alternans. Notably, at all CPA doses, alternation of SR Ca release occurred prior to alternation of diastolic SR Ca load as pacing frequency increased. Simultaneous optical mapping of SR Ca and V in the intact rabbit heart revealed that SERCA inhibition exacerbates pacing-induced SR Ca and APD alternans magnitude, particularly at fast pacing frequencies. Importantly, SR Ca release alternans always occurred before the onset of SR Ca load alternans. These findings suggest that even in settings of diminished SERCA function, relative refractoriness of RyR Ca release governs the onset of intracellular Ca alternans.
在每个兴奋 - 收缩偶联周期中，肌浆网（SR）的钙循环由兰尼碱受体（RyR）钙释放和肌浆网钙 - ATP酶（SERCA）钙摄取严格调控。我们之前表明，RyR不应期在完整兔心脏SR钙交替现象的起始中起关键作用，这促成了致心律失常的动作电位时程（APD）交替。最近的研究也表明，SERCA功能受损（心力衰竭的一个关键特征）与心脏交替现象和心律失常有关。然而，SERCA功能降低与SR钙交替现象之间的关系尚未完全清楚。使用电压敏感染料RH237和低亲和力钙指示剂Fluo - 5N - AM，在离体兔心脏（n = 10）中同时进行跨膜电位（V）和SR钙的光学映射。通过快速心室起搏诱导交替现象。用环匹阿尼酸（CPA；1 - 10 μM）抑制SERCA。SERCA抑制（1、5和10 μM的CPA）导致SR钙再摄取呈剂量依赖性减慢，时间常数（τ）从基线时的70.8 ± 3.5 ms分别增加到85.5 ± 6.6、129.9 ± 20.7和271.3 ± 37.6 ms（所有剂量与基线相比，P < 0.05）。在快速起搏频率下，CPA显著增加了SR钙和APD交替现象的幅度，在10 μM时最为明显（起搏周期长度 = 220 ms：SR钙交替现象幅度：57.1 ± 4.7对13.4 ± 8.9 AU；APD交替现象幅度3.8 ± 1.9对0.2 ± 0.19 AU；10 μM的CPA与基线相比，两者均P < 0.05）。SERCA抑制还促进了空间不一致交替现象的出现。值得注意的是，在所有CPA剂量下，随着起搏频率增加，SR钙释放的交替在舒张期SR钙负荷交替之前发生。在完整兔心脏中同时进行SR钙和V的光学映射显示，SERCA抑制加剧了起搏诱导的SR钙和APD交替现象的幅度，特别是在快速起搏频率下。重要的是，SR钙释放交替总是在SR钙负荷交替开始之前发生。这些发现表明，即使在SERCA功能降低的情况下，RyR钙释放的相对不应期仍控制着细胞内钙交替现象的起始。
