Miyauchi A, Notoya K, Mikuni-Takagaki Y, Takagi Y, Goto M, Miki Y, Takano-Yamamoto T, Jinnai K, Takahashi K, Kumegawa M, Chihara K, Fujita T
National Sanatorium Hyogo Chuo Hospital, Sanda, Hyogo 669-1515, Japan.
J Biol Chem. 2000 Feb 4;275(5):3335-42. doi: 10.1074/jbc.275.5.3335.
This paper documents for the first time a volume-sensitive Ca(2+) influx pathway in osteocytes, which transmits loading-induced signals into bone formation. Stretch loading by swelling rat and chicken osteocytes in hypo-osmotic solution induced a rapid and progressive increase of cytosolic calcium concentration, Ca(2+). The influx of extracellular Ca(2+) explains the increased Ca(2+) that paralleled the increase in the mean cell volume. Gadolinium chloride (Gd(3+)), an inhibitor of stretch- activated cation channels, blocked the Ca(2+) increase caused by hypotonic solutions. Also, the expression of alpha1C subunit of voltage-operated L-type Ca(2+) channels (alpha1C) is required for the hypotonicity-induced Ca(2+) increase judging from the effect of alpha1C antisense oligodeoxynucleotides. Parathyroid hormone (PTH) specifically potentiated the hypotonicity-induced Ca(2+) increase in a dose-dependent manner through the activation of adenyl cyclase. The increases induced by both PTH and hypotonicity were observed primarily in the processes of the osteocytes. In cyclically stretched osteocytes on flexible-bottomed plates, PTH also synergistically elevated the insulin-like growth factor-1 mRNA level. Furthermore, Gd(3+) and alpha1C antisense significantly inhibited the stretch-induced insulin-like growth factor-1 mRNA elevation. The volume-sensitive calcium influx pathways of osteocytes represent a mechanism by which PTH potentiates mechanical responsiveness, an important aspect of bone formation.
本文首次记录了骨细胞中一种对容积敏感的Ca(2+)内流途径，该途径将负荷诱导的信号传递至骨形成过程。通过在低渗溶液中膨胀大鼠和鸡的骨细胞进行牵张负荷，可诱导细胞溶质钙浓度Ca(2+)快速且持续增加。细胞外Ca(2+)的内流解释了与平均细胞体积增加平行的Ca(2+)升高。钆氯化物（Gd(3+)）作为牵张激活阳离子通道的抑制剂，可阻断低渗溶液引起的Ca(2+)增加。此外，从α1C反义寡脱氧核苷酸的作用判断，电压门控L型Ca(2+)通道（α1C）的α1C亚基表达是低渗诱导的Ca(2+)增加所必需的。甲状旁腺激素（PTH）通过激活腺苷酸环化酶，以剂量依赖的方式特异性增强低渗诱导的Ca(2+)增加。PTH和低渗诱导的增加主要在骨细胞的突起中观察到。在柔性底板上周期性牵张的骨细胞中，PTH还协同提高胰岛素样生长因子-1 mRNA水平。此外，Gd(3+)和α1C反义显著抑制牵张诱导的胰岛素样生长因子-1 mRNA升高。骨细胞的容积敏感钙内流途径代表了一种机制，通过该机制PTH增强机械反应性，这是骨形成的一个重要方面。
