Hatem S N, Bénardeau A, Rücker-Martin C, Marty I, de Chamisso P, Villaz M, Mercadier J J
Laboratorie de Cardiologie Moléculaire et Cellulaire, Université de Paris XI-CNRS URA 1159, Hôpital Marie Lannelongue, Le Plessis Robinson, France.
Circ Res. 1997 Mar;80(3):345-53. doi: 10.1161/01.res.80.3.345.
The excitation-contraction coupling process of human atrial myocytes was studied in voltage-clamped myocytes isolated from right atrial appendages obtained during cardiac surgery. Intracellular Ca2+ transients (Cai transients) were monitored with 0.1 mmol/L indo 1 added to the internal dialyzing solution. Ryanodine receptors (RyRs) and sarcomeric alpha-actinin were stained with specific antibodies and visualized using plane and confocal microscopy. L-Type Ca2+ current (Ica) elicited a prolonged Cai transient, with an initial rapidly activating phase (slope 1, 23.6 +/- 1.2 s-1) followed by a slowly activating phase (slope 2, 5.8 +/- 0.4 s-1; P < .001 versus slope 1), resulting in a dome-shaped Cai transient. Ryanodine (100 mumol/L) inhibited 79 +/- 6% of the Cai transient, indicating that it was due essentially to sarcoplasmic reticulum Ca2+ release. During step depolarizations, maximal activation of the Cai transient or tail current (Itail) (in cells dialyzed with Ca2+ buffer-free internal solution) preceded that of Ica and did not follow its voltage dependence (n = 12). Test pulses lasting from 5 to 150 milliseconds elicited a similar time course of both Cai transient and Itail (n = 5). In a given cell, the two components of the Cai transient could be dissociated by altering the intracellular Ca2+ load, by increasing the stimulation rate from 0.1 to 1 Hz, or by varying the amplitude of Ica. Immunostaining of atrial sections and isolated myocytes showed that a large number of RyRs were located not only in a subsarcolemmal position but also deeper inside the cell, in a regularly spaced transverse band pattern at the level of Z lines. Together, our results indicate that, in human atrial myocytes, Ica only partially controls the activation of RyRs, with the prolonged and dome-shaped Cai transient of these cells probably reflecting the activation of RyRs not coupled to L-type Ca2+ channels.
在心脏手术期间从右心耳分离出的电压钳制心肌细胞中，研究了人心房肌细胞的兴奋 - 收缩偶联过程。向内部透析液中添加0.1 mmol/L的indo 1以监测细胞内Ca2+瞬变（Cai瞬变）。用特异性抗体对兰尼碱受体（RyRs）和肌节α - 肌动蛋白进行染色，并使用平面和共聚焦显微镜观察。L型Ca2+电流（Ica）引发了一个延长的Cai瞬变，其初始为快速激活阶段（斜率1，23.6±1.2 s-1），随后是缓慢激活阶段（斜率2，5.8±0.4 s-1；与斜率1相比，P <.001），导致Cai瞬变呈圆顶状。兰尼碱（100 μmol/L）抑制了79±6%的Cai瞬变，表明其主要源于肌浆网Ca2+释放。在阶跃去极化期间，Cai瞬变或尾电流（Itail）（在用无Ca2+缓冲液的内部溶液透析的细胞中）的最大激活先于Ica的激活，且不遵循其电压依赖性（n = 12）。持续5至150毫秒的测试脉冲引发了Cai瞬变和Itail相似的时间进程（n = 5）。在给定的细胞中，通过改变细胞内Ca2+负荷、将刺激频率从0.1 Hz提高到1 Hz或改变Ica的幅度，可以分离Cai瞬变的两个成分。心房切片和分离的心肌细胞的免疫染色显示，大量的RyRs不仅位于肌膜下位置，还位于细胞内部更深的位置，在Z线水平呈规则间隔的横向带状模式。总之，我们的结果表明，在人心房肌细胞中，Ica仅部分控制RyRs的激活，这些细胞延长的圆顶状Cai瞬变可能反映了未与L型Ca2+通道偶联的RyRs的激活。
