Davidoff A J, Maki T M, Ellingsen O, Marsh J D
Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
J Mol Cell Cardiol. 1997 Jul;29(7):1791-803. doi: 10.1006/jmcc.1997.0406.
In addition to playing a significant role in cardiac excitation-contraction coupling, intracellular Ca2+ ([Ca2+]i) can regulate gene expression. While the mechanisms regulating expression of Ca2+ channels are not entirely defined, some evidence exists for Ca2+-dependent regulation. Using an adult ventricular myocyte culture system, we determined the effects of Ca2+ on: (1) abundance of mRNA for L-type Ca2+ channel alpha1 subunit (DHP receptor); (2) amount of DHP receptors; and (3) whole-cell Ca2+ current (ICa). Rat ventricular myocytes were cultured for 1-3 days in serum-free medium containing either normal (1.8 mM) or high (4.8 mM) Ca2+. Exposing myocytes to high Ca2+ rapidly elevated [Ca2+]i as determined by fura-2. Northern blot analysis revealed that culturing cells in high Ca2+ produced 1.5-fold increase in mRNA levels for the DHP receptor. The abundance of DHP receptors, determined by ligand binding, was two-fold greater in myocytes after 3 days in high Ca2+. Moreover, peak ICa was larger in myocytes cultured for 3 days in high Ca2+ (-17.8+/-1.5 pA/pF, n=26) than in control cells (-11.0+/-1.0 pA/pF, n=23). Voltage-dependent activation and inactivation, rates of current decay, as well as percent increases in ICa elicited by Bay K8644 were similar in all groups. Therefore, larger ICa is likely to represent a greater number of functional channels with unchanged kinetics. Our data support the conclusion that transient changes in [Ca2+]i can modulate DHP receptor mRNA and protein abundance, producing a corresponding change in functional Ca2+ channels in adult ventricular myocytes.
除了在心脏兴奋 - 收缩偶联中发挥重要作用外，细胞内Ca2+（[Ca2+]i）还可以调节基因表达。虽然调节Ca2+通道表达的机制尚未完全明确，但存在一些Ca2+依赖性调节的证据。我们使用成年心室肌细胞培养系统，确定了Ca2+对以下方面的影响：（1）L型Ca2+通道α1亚基（二氢吡啶受体，DHP受体）的mRNA丰度；（2）DHP受体的数量；（3）全细胞Ca2+电流（ICa）。将大鼠心室肌细胞在含有正常（1.8 mM）或高（4.8 mM）Ca2+的无血清培养基中培养1 - 3天。用fura - 2测定发现，将肌细胞暴露于高Ca2+会迅速升高[Ca2+]i。Northern印迹分析显示，在高Ca2+条件下培养细胞会使DHP受体的mRNA水平增加1.5倍。通过配体结合测定，在高Ca2+环境中培养3天后，肌细胞中DHP受体的丰度增加了两倍。此外，在高Ca2+中培养3天的肌细胞的ICa峰值（-17.8±1.5 pA/pF，n = 26）大于对照细胞（-11.0±1.0 pA/pF，n = 23）。所有组中电压依赖性激活和失活、电流衰减速率以及Bay K8644引起的ICa增加百分比均相似。因此，更大的ICa可能代表更多具有不变动力学的功能性通道。我们的数据支持这样的结论，即[Ca2+]i的瞬时变化可以调节DHP受体的mRNA和蛋白质丰度，从而使成年心室肌细胞中的功能性Ca2+通道产生相应变化。
