Short C L, Monk R D, Bushinsky D A, Krieger N S
Department of Medicine, University of Rochester School of Medicine and Dentistry, New York.
J Bone Miner Res. 1994 Aug;9(8):1159-66. doi: 10.1002/jbmr.5650090805.
We proposed a role for Na-Ca exchange in hormonally mediated bone resorption and recently characterized Na-dependent Ca transport in an osteoblast-like rat osteosarcoma cell line (UMR-106). To test whether calcemic agents alter Na(+)-Ca2+ exchange in osteoblasts, UMR cells were treated acutely or cultured in the absence or presence of calcemic agent for 24 h. Cells were then loaded with the Ca-sensitive dye fura-2 in the presence of 140 mM NaCl, no Ca, and the absence or presence of 0.3 mM ouabain. Cells were resuspended at 22 degrees C, and the fluorescence ratio at excitation wavelength of 340 and 380 nm was measured. An outward Na gradient was generated by removing extracellular Na and maintaining isotonicity with choline chloride. Na(+)-Ca2+ exchange was demonstrated by enhanced Ca uptake in ouabain-treated (Na-loaded) cells after the addition of 1.5 mM Ca. Acute addition of 10(-7) M PTH or 10(-6) M PGE2 had no effect on Na-dependent Ca uptake. However, 24 h treatment of cells with PTH, PGE2, or 1,25(OH)2D3 caused a dose-dependent inhibition of Na(+)-Ca2+ exchange. Using the Na-sensitive dye, SBFI, we also demonstrated that the effect was bidirectional; PTH inhibited Ca-dependent Na uptake comparably to its inhibition of Na-dependent Ca uptake. The effects of the calcemic agents were mimicked by 24 h treatment of the cells with 1 microM forskolin or 2 microM PMA.(ABSTRACT TRUNCATED AT 250 WORDS)
我们提出钠钙交换在激素介导的骨吸收中发挥作用，并且最近对成骨细胞样大鼠骨肉瘤细胞系（UMR - 106）中钠依赖性钙转运进行了表征。为了测试血钙调节剂是否会改变成骨细胞中的钠钙交换，将UMR细胞进行急性处理，或在无或有血钙调节剂的情况下培养24小时。然后在存在140 mM氯化钠、无钙以及存在或不存在0.3 mM哇巴因的情况下，用钙敏感染料fura - 2加载细胞。将细胞重悬于22摄氏度，测量激发波长为340和380 nm时的荧光比率。通过去除细胞外钠并用氯化胆碱维持等渗来产生外向钠梯度。在添加1.5 mM钙后，哇巴因处理（钠加载）的细胞中钙摄取增加，证明了钠钙交换。急性添加10(-7) M甲状旁腺激素（PTH）或10(-6) M前列腺素E2（PGE2）对钠依赖性钙摄取没有影响。然而，用PTH、PGE2或1,25(OH)2D3处理细胞24小时会导致钠钙交换的剂量依赖性抑制。使用钠敏感染料SBFI，我们还证明这种作用是双向的；PTH抑制钙依赖性钠摄取与其抑制钠依赖性钙摄取相当。用1 microM福司可林或2 microM佛波酯（PMA）处理细胞24小时可模拟血钙调节剂的作用。（摘要截短于250字）
