Centro de Estudios Moleculares de la Célula, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
J Gen Physiol. 2010 Oct;136(4):455-67. doi: 10.1085/jgp.200910397. Epub 2010 Sep 13.
Tetanic electrical stimulation induces two separate calcium signals in rat skeletal myotubes, a fast one, dependent on Cav 1.1 or dihydropyridine receptors (DHPRs) and ryanodine receptors and related to contraction, and a slow signal, dependent on DHPR and inositol trisphosphate receptors (IP(3)Rs) and related to transcriptional events. We searched for slow calcium signals in adult muscle fibers using isolated adult flexor digitorum brevis fibers from 5-7-wk-old mice, loaded with fluo-3. When stimulated with trains of 0.3-ms pulses at various frequencies, cells responded with a fast calcium signal associated with muscle contraction, followed by a slower signal similar to one previously described in cultured myotubes. Nifedipine inhibited the slow signal more effectively than the fast one, suggesting a role for DHPR in its onset. The IP(3)R inhibitors Xestospongin B or C (5 µM) also inhibited it. The amplitude of post-tetanic calcium transients depends on both tetanus frequency and duration, having a maximum at 10-20 Hz. At this stimulation frequency, an increase of the slow isoform of troponin I mRNA was detected, while the fast isoform of this gene was inhibited. All three IP(3)R isoforms were present in adult muscle. IP(3)R-1 was differentially expressed in different types of muscle fibers, being higher in a subset of fast-type fibers. Interestingly, isolated fibers from the slow soleus muscle did not reveal the slow calcium signal induced by electrical stimulus. These results support the idea that IP(3)R-dependent slow calcium signals may be characteristic of distinct types of muscle fibers and may participate in the activation of specific transcriptional programs of slow and fast phenotype.
强直性电刺激在大鼠骨骼肌肌管中诱导两个独立的钙信号，一个是快速信号，依赖于 Cav1.1 或二氢吡啶受体（DHPR）和兰尼碱受体，与收缩有关，另一个是缓慢信号，依赖于 DHPR 和肌醇三磷酸受体（IP3R），与转录事件有关。我们使用从小鼠 5-7 周龄的分离的伸趾短肌纤维，加载 fluo-3，来寻找成年肌肉纤维中的缓慢钙信号。当用各种频率的 0.3-ms 脉冲串刺激时，细胞会产生与肌肉收缩相关的快速钙信号，然后是一个类似于以前在培养的肌管中描述的较慢信号。硝苯地平比快速信号更有效地抑制缓慢信号，这表明 DHPR 在其起始中起作用。IP3R 抑制剂 Xestospongin B 或 C（5 µM）也抑制了它。强直后钙瞬变的幅度取决于强直频率和持续时间，在 10-20 Hz 时达到最大值。在这种刺激频率下，检测到慢型肌钙蛋白 I mRNA 的增加，而该基因的快型则受到抑制。三种 IP3R 同工型都存在于成年肌肉中。IP3R-1 在不同类型的肌肉纤维中有差异表达，在一部分快型纤维中表达较高。有趣的是，电刺激诱导的缓慢钙信号在分离的慢型比目鱼肌纤维中没有被揭示。这些结果支持这样的观点，即 IP3R 依赖性缓慢钙信号可能是特定类型的肌肉纤维的特征，并且可能参与慢型和快型表型的特定转录程序的激活。
