Lundgren T, Linde A
Department of Oral Biochemistry, Faculty of Odontology, Medicinaregatan 7 B, S-413 90 Göteborg University, Göteborg, Sweden.
Calcif Tissue Int. 1997 Jan;60(1):79-85. doi: 10.1007/s002239900189.
Odontoblasts participate actively in the transport and accumulation of Ca2+ ions to the mineralization front during dentinogenesis. These cells are known to carry membrane-bound ATP-driven pumps and Na+/Ca2+ antiports for Ca2+ extrusion, but little is known about Ca2+ influx mechanisms into these cells. It has been shown that the administration of Ca2+ channel blockers in vivo strongly impairs Ca2+ uptake in the mineral phase during dentinogenesis in the rat; the present in vitro study is aimed at further elucidating odontoblast Ca2+ uptake mechanisms. Dissected rat incisor odontoblasts exhibited a pronounced fluorescence when incubated with a fluorescently-labeled (STBodipy) dihydropyridine, which is specific for voltage-gated Ca2+ channels of the L-type, and this binding was competitively abolished by nifedipine. As assayed by fluorescence spectrometry, odontoblast Ca2+ uptake was enhanced by the agonistic dihydropyridine BAYK-8644 (5 micro;M) as well as by plasma membrane depolarization in a high K+ (120 mM) medium. The Ca2+ uptake after depolarization was impaired by nifedipine (5 micro;M). When treated with the Ca2+-ATPase inhibitor cyclopiazonic acid (CPA; 10 micro;M), a nonvoltage-gated uptake of 45Ca2+ was identified. This uptake was not influenced by nifedipine (20 micro;M) but was impaired by lanthanum ions (200 micro;M). A nonvoltage-gated uptake of Mn2+ into CPA-treated cells could be traced using the fura-2 quenching technique. This CPA-induced Ca2+ flux was not caused by an alteration of the plasma membrane potential, as assayed with di-8-ANEPPS. The results demonstrate that Ca2+ flux into dentinogenically active odontoblasts occurs through voltage-gated Ca2+ channels of the L-type and by nonvoltage-gated, agonist-sensitive Ca2+ uptake pathways.
成牙本质细胞在牙本质形成过程中积极参与钙离子向矿化前沿的转运和积累。已知这些细胞携带有膜结合的ATP驱动泵和用于钙离子排出的钠/钙反向转运体，但关于钙离子流入这些细胞的机制却知之甚少。研究表明，在体内给予钙离子通道阻滞剂会强烈损害大鼠牙本质形成过程中矿化相的钙离子摄取；本体外研究旨在进一步阐明成牙本质细胞的钙离子摄取机制。当用荧光标记的（STBodipy）二氢吡啶（一种对L型电压门控钙离子通道具有特异性的物质）孵育时，解剖的大鼠切牙成牙本质细胞呈现出明显的荧光，并且这种结合被硝苯地平竞争性消除。通过荧光光谱法测定，激动性二氢吡啶BAYK - 8644（5微摩尔）以及在高钾（120毫摩尔）培养基中的质膜去极化增强了成牙本质细胞的钙离子摄取。去极化后的钙离子摄取被硝苯地平（5微摩尔）损害。当用钙离子ATP酶抑制剂环匹阿尼酸（CPA；10微摩尔）处理时，鉴定出一种非电压门控的45钙离子摄取。这种摄取不受硝苯地平（20微摩尔）影响，但受到镧离子（200微摩尔）损害。使用fura - 2猝灭技术可以追踪锰离子进入经CPA处理细胞的非电压门控摄取。用di - 8 - ANEPPS测定表明，这种CPA诱导的钙离子通量不是由质膜电位改变引起的。结果表明，钙离子流入具有牙本质形成活性的成牙本质细胞是通过L型电压门控钙离子通道以及非电压门控、激动剂敏感的钙离子摄取途径发生的。
