Lundquist P, Lundgren T, Gritli-Linde A, Linde A
Department of Oral Biochemistry, Göteborg University, Sweden.
Calcif Tissue Int. 2000 Jul;67(1):60-7. doi: 10.1007/s00223001098.
In odontoblasts as well as osteoblasts, a number of mechanisms for the inflow and extrusion of Ca2+ have been demonstrated. The entrance of Ca2+ ions into odontoblasts occurs mainly through voltage-gated calcium channels. Extrusion of Ca2+ is found to be an ATP-dependent process and, in addition, Na+/Ca2+-antiports exist, which are provoked by extracellular Na+. The aim of this study was to identify the Na+/Ca2+-antiport isoforms expressed in dentinogenically active rat incisor odontoblasts and to make a comparison with different osteoblastic cells. Using RT-PCR and RNAse protection assay, we demonstrated the expression of three different isoforms, NaCa 3, 7, and 10, of the NCX1-encoded antiport in odontoblasts and osteoblastic cells. When incubated in the presence of Na+, dissected rat incisor odontoblasts as well as the osteoblastic cells extruded Ca2+ ions, as detected by chlorotetracycline and Fura-2 fluorometry, thus supporting a physiological role for the detected isoform expression. Odontoblasts and rat calvarial osteoblasts, as well as osteoblast-like cell lines UMR-106.01 and Saos-2, were shown to exhibit identical phenotypes of Na+/Ca2+-antiport isoform expression, different from the expression patterns of other tissues. The significance of this specific expression pattern is unknown, but there is a possibility that it is in some way related to the unique demands on these cell types to produce mineralized connective tissue.
在成牙本质细胞和成骨细胞中，已证实存在多种Ca2+流入和流出的机制。Ca2+离子进入成牙本质细胞主要通过电压门控钙通道。发现Ca2+的流出是一个依赖ATP的过程，此外，还存在Na+/Ca2+反向转运体，其由细胞外Na+激发。本研究的目的是鉴定在牙本质发生活跃的大鼠切牙成牙本质细胞中表达的Na+/Ca2+反向转运体亚型，并与不同的成骨细胞进行比较。通过逆转录聚合酶链反应（RT-PCR）和核糖核酸酶保护分析，我们证实了成牙本质细胞和成骨细胞中由NCX1编码的反向转运体的三种不同亚型NaCa 3、7和10的表达。当在有Na+存在的情况下孵育时，通过氯四环素和Fura-2荧光测定法检测到，分离的大鼠切牙成牙本质细胞以及成骨细胞会排出Ca2+离子，从而支持了所检测到的亚型表达具有生理作用。结果表明，成牙本质细胞、大鼠颅骨成骨细胞以及成骨样细胞系UMR-106.01和Saos-2表现出相同的Na+/Ca2+反向转运体亚型表达表型，这与其他组织的表达模式不同。这种特定表达模式的意义尚不清楚，但有可能它在某种程度上与这些细胞类型产生矿化结缔组织的独特需求有关。
