Broad L M, Powis D A, Taylor C W
Neuroscience Group, Faculty of Medicine and Health Sciences, University of Newcastle, NSW, Australia.
Biochem J. 1996 Jun 15;316 ( Pt 3)(Pt 3):759-64. doi: 10.1042/bj3160759.
Differentiation of BC3H1 cells leads to expression of a variety of proteins characteristic of smooth muscle and to changes in the behaviour of intracellular Ca2+ stores. Treatment of both differentiated and undifferentiated cells with thapsigargin (2 microM) emptied their intracellular Ca2+ stores, and in the presence of extracellular Ca2+ caused an increase in cytosolic [Ca2+] that rapidly reversed after its removal. The amplitudes of these capacitative Ca2+ entry signals were 101 +/- 8 nM (n = 42) in differentiated cells and 188 +/- 16 nM (n = 35) in undifferentiated cells. Mn2+ entry in thapsigargin-treated cells, measured by recording the quenching of cytosolic fura 2 fluorescence, was 374 +/- 26% (n = 34) and 154 +/- 7% (n = 41) of control rates in differentiated and undifferentiated cells, respectively. Empty stores caused Ba2+ entry to increase to 282 +/- 20% (n = 8) of its basal rate in differentiated cells and to 187 +/- 20% (n = 8) in undifferentiated cells. Rates of Ca2+ extrusion, measured after rapid removal of extracellular Ca2+ from cells in which capacitative Ca2+ entry had been activated, were similar in differentiated (t1/2 = 23 +/- 2 s, n = 7) and undifferentiated (23 +/- 1 s, n = 6) cells. The different relationships between capacitative Ca2+ and Mn2+ signals are not, therefore, a consequence of more active Ca2+ extrusion mechanisms in differentiated cells, nor are they a consequence of different fura 2 loadings in the two cell types. We conclude that during differentiation of BC3Hl cells, the cation selectivity of the capacitative pathway changes, becoming relatively more permeable to Mn2+ and Ba2+. The change may result either from expression of a different capacitative pathway or from modification of the permeation properties of a single pathway.
BC3H1细胞的分化导致多种平滑肌特征性蛋白的表达以及细胞内钙库行为的改变。用毒胡萝卜素（2微摩尔）处理分化和未分化细胞均会排空其细胞内钙库，并且在细胞外钙存在的情况下会导致胞质[Ca2+]升高，在去除细胞外钙后迅速恢复。这些容量性钙内流信号的幅度在分化细胞中为101±8纳摩尔（n = 42），在未分化细胞中为188±16纳摩尔（n = 35）。通过记录胞质fura 2荧光淬灭来测量，毒胡萝卜素处理的细胞中Mn2+内流在分化细胞和未分化细胞中分别为对照速率的374±26%（n = 34）和154±7%（n = 41）。钙库排空导致Ba2+内流在分化细胞中增加至基础速率的282±20%（n = 8），在未分化细胞中增加至187±20%（n = 8）。在容量性钙内流已被激活的细胞中快速去除细胞外钙后测量的Ca2+外排速率，在分化细胞（t1/2 = 23±2秒，n = 7）和未分化细胞（23±1秒，n = 6）中相似。因此，容量性Ca2+和Mn2+信号之间的不同关系，既不是分化细胞中更活跃的Ca2+外排机制的结果，也不是两种细胞类型中fura 2负载不同的结果。我们得出结论，在BC3Hl细胞分化过程中，容量性途径的阳离子选择性发生变化，对Mn2+和Ba2+的通透性相对增加。这种变化可能是由于不同容量性途径的表达，或者是单一途径通透特性的改变。
