Nanci A, Fortin M, Ghitescu L
Department of Stomatology, Université de Montréal, Quebec, Canada.
Anat Rec. 1996 Jun;245(2):219-34. doi: 10.1002/(SICI)1097-0185(199606)245:2<219::AID-AR9>3.0.CO;2-R.
Biochemical, (immuno)cytochemical, and radioautographic data accumulated over several years have lead to the view that ameloblasts carry out both secretory and degradative functions throughout amelogenesis. Whereas it has been assumed that maturation stage ameloblasts endocytose aged enamel proteins from the enamel layer, the origin of the newly formed ones detected in the endosomal/lysosomal compartment of ameloblasts from all stages remains to be elucidated. One possible source is from secretory products released ectopically along basolateral surfaces.
To test this hypothesis, we have investigated, using colloidal gold immunocytochemistry, whether plasma proteins (albumin and alpha 2HS-glycoprotein) found in the interstitial fluid are endocytosed by rat incisor ameloblasts and other cells from hard and soft tissues. Rat albumin, tagged with dinitrophenol, was injected intravenously to trace the movement of this protein.
Plasma proteins were immunodetected along the baso-lateral surfaces and in multivesicular bodies of ameloblasts where enamel proteins were also found. By 2 hours following intravenous administration of dinitrophenylated albumin, the tracer had left the blood and diffused into the enamel organ and between odontoblasts and osteoblasts. The tracer was also found in multivesicular bodies of all cells examined.
The uptake of albumin by many different cell types suggests that this process is not restricted to ameloblasts and likely occurs in a nonselective manner. Hence, baso-lateral uptake in ameloblasts may play a role not only in the continuous removal of plasma proteins leaking from the blood, but also of enamel proteins 'dumped' laterally between these cells. Likewise, odontoblasts may use the same mechanism to internalize some of the plasma proteins and any enamel protein that diffuse toward them.
多年积累的生化、（免疫）细胞化学和放射自显影数据表明，成釉细胞在整个釉质形成过程中兼具分泌和降解功能。虽然一直认为成熟阶段的成釉细胞会从釉质层内吞老化的釉质蛋白，但在所有阶段成釉细胞的内体/溶酶体区室中检测到的新形成蛋白的来源仍有待阐明。一个可能的来源是沿基底外侧表面异位释放的分泌产物。
为了验证这一假设，我们使用胶体金免疫细胞化学方法研究了间质液中的血浆蛋白（白蛋白和α2HS-糖蛋白）是否被大鼠切牙成釉细胞以及来自硬组织和软组织的其他细胞内吞。静脉注射用二硝基苯酚标记的大鼠白蛋白，以追踪该蛋白的移动。
在成釉细胞的基底外侧表面和多囊泡体中免疫检测到血浆蛋白，在这些地方也发现了釉质蛋白。静脉注射二硝基苯基化白蛋白2小时后，示踪剂已离开血液并扩散到釉器以及成牙本质细胞和成骨细胞之间。在所有检查的细胞的多囊泡体中也发现了示踪剂。
许多不同细胞类型对白蛋白的摄取表明这一过程不仅限于成釉细胞，而且可能以非选择性方式发生。因此，成釉细胞的基底外侧摄取可能不仅在持续清除从血液中漏出的血浆蛋白方面起作用，而且在这些细胞之间侧向“倾倒”的釉质蛋白清除方面也起作用。同样，成牙本质细胞可能使用相同的机制内化一些血浆蛋白以及任何向它们扩散的釉质蛋白。
