Ca2+ images and K+ current during depolarization in smooth muscle cells of the guinea-pig vas deferens and urinary bladder
Ca2+ images and K+ current during depolarization in smooth muscle cells of the guinea-pig vas deferens and urinary bladder
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DOI：
10.1111/j.1469-7793.1998.705bj.x
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发表时间：
1998-08-01
影响因子：
5.5
通讯作者：
Bolton, TB
中科院分区：
文献类型：
--
作者：
Imaizumi, Y;Torii, Y;Bolton, TB
1.用Fluo-3和激光扫描共聚焦显微镜同时检测新鲜分离的豚鼠输精管和膀胱单个平滑肌细胞的电活动和细胞内钙离子浓度([Ca~(2+)])。在电压钳下，从-60到0或+10 mV每8ms获得一次图像，持续50ms，结果显示，在去极化后20ms内，可以在5到20个小的(直径2微米)的“热点”中检测到[Ca~(2+)]的升高，其中95%以上位于细胞膜1.5微米范围内。S每隔30分钟去极化激活同一地点的热点。Cd~(2+)或异搏定均可阻断兴奋点和钙激活的钾电流(I-K，I-Ca)。咖啡因几乎消除了热点，并显著降低了I-K、I-Ca。环匹阿松酸可使基础整体[Ca~(2+)]升高，降低去极化时热点[Ca~(2+)]和I-K、I-Ca波幅的升高。这些结果提示，钙离子内流导致了钙离子诱导的钙离子释放(CICR)。在电压钳下，热点[Ca~(2+)]与[K]、[Ca~(2+)]的升高密切相关，并在去极化开始的20ms内达到峰值，但整个细胞区的[Ca~(2+)]升高较慢。阶梯除极至正电位至-20 mV时，热点增大并合并，导致整体[Ca~(2+)]升高和收缩。在电流钳下，诱发动作电位上击过程中也出现了钙离子热点。结果表明，在动作电位的早期阶段，钙离子的进入从离散的质膜下钙离子储存部位引起CICR，产生扩散的热点以启动收缩。细胞质膜上钙依赖的K+通道的激活引发了I-K、I-Ca和动作电位的复极化。
1. Electrical events and intracellular calcium concentration ([Ca2+]) imaged using fluo-3 and laser scanning confocal microscopy were simultaneously monitored in single smooth muscle cells freshly isolated from guinea-pig was deferens or urinary bladder.2. Images obtained every 8 ms, during stepping from -60 to 0 or +10 mV for 50 ms under voltage clamp, showed that a rise in [Ca2+] could be detected within 20 ms of depolarization in five to twenty small (< 2 mu m diameter) 'hot spots', over 95% of which were located within 1.5 mu m of the cell membrane. Depolarization at 30 s intervals activated hot spots at the same places.3. Cd2+ or verapamil abolished both hot spots and Ca2+-activated K+ current (I-K,I-Ca). Caffeine almost abolished hot spots and markedly reduced I-K,I-Ca. Cyclopiazonic acid, which raised basal global [Ca2+], decreased the rise in hot spot [Ca2+] and I-K,I-Ca amplitude during depolarization. These results suggest that Ca2+ entry caused Ca2+-induced Ca2+ release (CICR).4. Under voltage clamp, hot spot [Ca2+] closely paralleled the rise in I-K,I-Ca and reached a peak within 20 ms of the start of depolarization, but the rise in global [Ca2+] over the whole cell area was much slower. Step depolarization to potentials positive to -20 mV caused hot spots to grow in size and coalesce, leading to a rise in global [Ca2+] and contraction. Ca2+ hot spots also occurred during the up-stroke of an evoked action potential under current clamp.5. It is concluded that the entry of Ca2+ in the early stages of an action potential evokes CICR from discrete subplasmalemma Ca2+ storage sites slid generates hot spots that spread to initiate a contraction. The activation of Ca2+-dependent K+ channels in the plasmalemma over hot spots initiates I-K,I-Ca and action potential repolarization.