Two-step Ca2+ intracellular release underlies excitation-contraction coupling in mouse urinary bladder myocytes
Two-step Ca2+ intracellular release underlies excitation-contraction coupling in mouse urinary bladder myocytes
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DOI：
10.1152/ajpcell.00409.2005
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发表时间：
2006-02-01
影响因子：
5.5
通讯作者：
Imaizumi, Y
中科院分区：
文献类型：
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作者：
Morimura, K;Ohi, Y;Imaizumi, Y
在大多数平滑肌细胞（SMCs）中，Ca2+诱导的Ca2+释放（CICR）与通过电压依赖性Ca2+通道（VDCCs）的Ca2+内流对兴奋-收缩耦合的相对贡献尚未确定。本研究旨在解决小鼠膀胱（UB）平滑肌细胞（UBSMCs）的这一问题。在电压或电流箝位条件下获得共聚焦Ca2+图像。当UBSMCs被30 ms去极化至0 mV激活时，细胞内Ca2+浓度（[Ca2+](i)）在细胞膜下方的几个小的离散区域增加。这些Ca2+“热点”然后以Ca2+波的形式缓慢地通过肌质传播，即使在复极化后也会继续传播。较短的去极化（5ms）只引起少量Ca2+火花，并且迅速下降。Ca2+火花或热点的数量与脱极化持续时间密切相关，范围约为5-20 ms。有一个明显的阈值去极化持续时间约为10 ms，在这段时间内可以诱导足够的Ca2+瞬态扩散到全身，然后诱导收缩。在移液液中加入100 μ M瑞诺定不改变静息[Ca2+](i)或VDCC电流，但消除了去极化引起的Ca2+热点。施用3 μ M xestospongin C可减少乙酰胆碱诱导的Ca2+释放，但不影响去极化诱导的Ca2+事件。在组织节段中加入100 μ M瑞诺定可显著降低直接电刺激引起的收缩幅度。总之，单一动作电位触发的全局[Ca2+](i)上升主要不是由于Ca2+通过vdcc内流，而是归因于随后的两步CICR。
The relative contributions of Ca2+-induced Ca2+ release (CICR) versus Ca2+ influx through voltage-dependent Ca2+ channels (VDCCs) to excitation-contraction coupling has not been defined in most smooth muscle cells (SMCs). The present study was undertaken to address this issue in mouse urinary bladder (UB) smooth muscle cells (UBSMCs). Confocal Ca2+ images were obtained under voltage-or current-clamp conditions. When UBSMCs were activated by a 30-ms depolarization to 0 mV, intracellular Ca2+ concentration ([Ca2+](i)) increased in several small, discrete areas just beneath the cell membrane. These Ca2+ "hot spots" then spread slowly through the myoplasm as Ca2+ waves, which continued even after repolarization. Shorter depolarizations (5 ms) elicited only a few Ca2+ sparks, which declined quickly. The number of Ca2+ sparks, or hot spots, was closely related to the depolarization duration in the range of similar to 5-20 ms. There was an apparent threshold depolarization duration of similar to 10 ms within which to induce enough Ca2+ transients to spread globally and then induce a contraction. Application of 100 mu M ryanodine to the pipette solution did not change the resting [Ca2+](i) or the VDCC current, but it did abolish Ca2+ hot spots elicited by depolarization. Application of 3 mu M xestospongin C reduced ACh-induced Ca2+ release but did not affect depolarization-induced Ca2+ events. The addition of 100 mu M ryanodine to tissue segments markedly reduced the amplitude of contractions triggered by direct electrical stimulation. In conclusion, global [Ca2+](i) rise triggered by a single action potential is not due mainly to Ca2+ influx through VDCCs but is attributable to the subsequent two-step CICR.