Properties of the depolarization-activated calcium and barium entry in osteoblast-like cells.
Properties of the depolarization-activated calcium and barium entry in osteoblast-like cells.
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发表时间：
1989-01
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通讯作者：
D. Yamaguchi;J. Green;C. Kleeman;S. Muallem
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作者：
D. Yamaguchi;J. Green;C. Kleeman;S. Muallem
利用Fura 2测量游离收缩Ca2+ ([Ca2+]i)和Ba2+ ([Ba2+]i)浓度，以鉴定和表征去极化激活的Ca2+和Ba2+进入成骨样细胞质膜的特性。在两种成骨细胞系UMR-106和MC3T3-E1以及从大鼠长骨和大鼠新生颅骨分离的成骨细胞中证实了该途径的存在。随后在骨肉瘤细胞系UMR-106中对该通路进行了表征。高K+的细胞去极化后，[Ca2+]i增加，这依赖于介质Ca2+。Ba2+离子使细胞去极化并通过该途径运输。Mg2+离子干扰Ca2+和Ba2+的进入。在140 mM KCl和1 mM MgCl2条件下，该通路可被Ca2+或Ba2+饱和。Ca2+的表观亲和力为0.78 mM， Ba2+的表观亲和力为1.82 mM。Ca2+或Ba2+进入细胞被低浓度的尼卡地平、地尔硫卓、维拉帕米和La3+阻断。在没有增加[Ca2+]i或[Ba2+]i的情况下，该通路在去极化后约5分钟内失活。当允许[Ca2+]i或[Ba2+]i增加时，该途径在约20 s内失活。这些特性表明Ca2+和Ba2+的进入是由l型，去极化激活的Ca2+通道在成骨细胞中介导的。这些通道的活性随细胞体积的增加或减少变化不大。因此，我们得出结论，这些途径不提供Ca2+进入途径所需的启动体积减少成骨细胞。
Measurements of free cystolic Ca2+ ([Ca2+]i) and Ba2+ ([Ba2+]i) concentrations with Fura 2 were used to identify and characterize the properties of a depolarization-activated Ca2+ and Ba2+ entry in the plasma membrane of osteoblast-like cells. The presence of this pathway was demonstrated in two osteoblastic cell lines, UMR-106 and MC3T3-E1 and osteoblasts isolated from rat long bone and rat neonatal calvariae. Subsequent characterization of the pathway was performed in the osteosarcoma cell line UMR-106. Depolarization of the cells with high medium K+ was followed by an increase in [Ca2+]i which was dependent on medium Ca2+. Ba2+ ions depolarized the cells and were transported by this pathway. Mg2+ ions interfered with Ca2+ and Ba2+ entry. At 140 mM KCl and 1 mM MgCl2, the pathway could be saturated with Ca2+ or Ba2+. The apparent affinity for Ca2+ was 0.78 mM and for Ba2+ 1.82 mM. Ca2+ or Ba2+ entry into the cells was blocked by low concentrations of nicardipine, diltiazem, verapamil, and La3+. In the absence of an increase in [Ca2+]i or [Ba2+]i, the pathway inactivated within about 5 min after depolarization. When [Ca2+]i or [Ba2+]i was allowed to increase, the pathway inactivated within about 20 s. These properties suggest that Ca2+ and Ba2+ entry are mediated by an L-type, depolarization-activated Ca2+ channel in osteoblasts. The activity of these channels changes little with an increase or decrease in cell volume. Thus, it is concluded that these pathways do not provide the Ca2+ entry pathway required for initiation of volume decrease by osteoblasts.