Data from: Cellular hypertrophy and increased susceptibility to spontaneous calcium-release of rat left atrial myocytes due to elevated afterload

Atrial remodeling due to elevated arterial pressure predisposes the heart to atrial fibrillation (AF). Although abnormal sarcoplasmic reticulum (SR) function has been associated with AF, there is little information on the effects of elevated afterload on atrial Ca2+-handling. We investigated the effects of ascending aortic banding (AoB) on Ca2+-handling in rat isolated atrial myocytes in comparison to age-matched sham-operated animals (Sham). Myocytes were either labelled for ryanodine receptor (RyR) or loaded with fluo-3-AM and imaged by confocal microscopy. AoB myocytes were hypertrophied in comparison to Sham controls (P<0.0001). RyR labeling was localized to the z-lines and to the cell edge. There were no differences between AoB and Sham in the intensity or pattern of RyR-staining. In both AoB and Sham, electrical stimulation evoked robust SR Ca2+-release at the cell edge whereas Ca2+ transients at the cell center were much smaller. Western blotting showed a decreased L-type Ca channel expression but no significant changes in RyR or RyR phosphorylation or in expression of Na+/Ca2+ exchanger, SR Ca2+ ATPase or phospholamban. Mathematical modeling indicated that [Ca2+]i transients at the cell center were accounted for by simple centripetal diffusion of Ca2+ released at the cell edge. In contrast, caffeine (10 mM) induced Ca2+ release was uniform across the cell. The caffeine-induced transient was smaller in AoB than in Sham, suggesting a reduced SR Ca2+-load in hypertrophied cells. There were no significant differences between AoB and Sham cells in the rate of Ca2+ extrusion during recovery of electrically-stimulated or caffeine-induced transients. The incidence and frequency of spontaneous Ca2+-transients following rapid-pacing (4 Hz) was greater in AoB than in Sham myocytes. In conclusion, elevated afterload causes cellular hypertrophy and remodeling of atrial SR Ca2+-release.

动脉压力升高引发的心房重构会使心脏易患心房颤动（atrial fibrillation, AF）。尽管肌浆网（sarcoplasmic reticulum, SR）功能异常与心房颤动存在关联，但目前关于后负荷升高对心房钙处理（Ca²⁺-handling）的影响尚缺乏相关研究。本研究以年龄匹配的假手术组（sham-operated animals, Sham）大鼠为对照，探究了升主动脉缩窄术（ascending aortic banding, AoB）对分离的大鼠心房肌细胞钙处理的影响。实验中，我们对心房肌细胞分别进行雷诺丁受体（ryanodine receptor, RyR）标记，或使用fluo-3-AM进行负载，随后通过共聚焦显微镜成像。与假手术对照组相比，升主动脉缩窄组的肌细胞呈现肥大表型（P<0.0001）。雷诺丁受体的标记信号定位于Z盘（z-lines）与细胞边缘，且升主动脉缩窄组与假手术组的雷诺丁受体染色强度与染色模式均无显著差异。在两组样本中，电刺激均可在细胞边缘引发强烈的肌浆网钙释放，但细胞中心的钙瞬变幅度明显更小。蛋白质免疫印迹（Western blotting）结果显示，L型钙通道（L-type Ca channel）的表达量下调，但雷诺丁受体、雷诺丁受体磷酸化水平，以及钠钙交换体（Na+/Ca2+ exchanger）、肌浆网钙ATP酶（SR Ca2+ ATPase）与受磷蛋白（phospholamban）的表达量均无显著变化。数学模型分析表明，细胞中心的细胞内钙瞬变（[Ca2+]i transients）可通过细胞边缘释放的钙离子向心性简单扩散来解释。与之相反，咖啡因（10 mM）诱导的钙释放在整个细胞内分布均匀。升主动脉缩窄组的咖啡因诱导钙瞬变幅度小于假手术组，提示肥大肌细胞的肌浆网钙负荷（SR Ca2+-load）有所降低。在电刺激或咖啡因诱导的钙瞬变恢复过程中，两组肌细胞的钙排出速率无显著差异。快速起搏（4 Hz）后，升主动脉缩窄组肌细胞的自发性钙瞬变发生率与频率均高于假手术组。综上，后负荷升高会引发心房肌细胞肥大以及心房肌浆网钙释放的重构。