INTESTINAL CA2+ TRANSPORT: VITAMIN D-DEPENDENT MECHANISM

维生素D依赖的钙转运机制研究进展 在整个肠道，我们从大鼠的肠道中制备了膜泡 上皮细胞(肠细胞)，并观察高尔基体膜囊泡 与侧基底部(L-B)相比，显示最高的钙摄取 微绒毛(MV)膜泡。这种对钙的摄取是特别的 依赖于维生素D的活性代谢物1，25(OH)2D3 由这笔赠款支持的研究表明，这种钙摄取是由于 与膜中的非酯化脂肪酸(NEFAs)结合，并被 与磷脂酶A活性增加有关。制备的膜 从分离的肠上皮细胞中提取的钙离子结合显著减少，且更好 表现出依赖维生素D的ATP-需要钙摄取，特别是 十二指肠绒毛细胞(与隐窝细胞相比)。追寻 这些发现进一步建议：1)界定非正规金融机构的角色， 磷脂和磷脂酶在血管紧张素转换酶分子机制中的作用 在肠道吸收钙的过程中将其隔离，2)净化 L-B膜Ca~(2+)-ATPase可能与ATP依赖的Ca~2+有关 3)研究1，25(OH)2D3 影响Ca~(2+)-ATPase功能的基因组机制或通过 酶的翻译后激活。我们还将努力确定 如果1，25-(OH)2D3刺激高尔基体蛋白质的合成或出现 L-B膜对脂质代谢有重要作用。1，25(OH)2D3的作用 对钙-三磷酸腺苷酶的信使核糖核酸进行了研究。这些参数的更改 与肠上皮细胞分化有关的研究将被强调。因为在那里 有证据表明1，25(OH)2D3依赖的钙转运实际上是， 依赖于肠细胞分化，它似乎是一个理想的系统 增加我们对组织分化和组织结构的理解 与特定肠道功能的关系。肠道调节 钙转运是钙稳态的基础。因此，这些 研究将有助于理解骨质疏松症的病理生理学， 肾结石和肠道疾病对钙吸收的影响 和钙代谢。

In previous studies on the mechanism of vitamin D-dependent Ca2+ transport across the intestine, we prepared membrane vesicles from rat intestinal epithelial cells (enterocytes) and observed that Golgi membrane vesicles demonstrated the highest Ca2+ uptake when compared with lateral-basal (L-B) and microvillus (MV) membrane vesicles. This Ca2+ uptake was specifically dependent on 1,25(OH)2D3, the active metabolite of vitamin D. Recent studies, supported by this grant, have shown that this Ca2+ uptake was due to binding to non-esterified fatty acids (NEFAs) in the membranes and was associated with an increased phospholipase A activity. Membranes prepared from isolated enterocytes had markedly decreased Ca2+ binding and better demonstrated a vitamin D-dependent ATP-requiring Ca2+ uptake, particularly for duodenal villus cells (as contrasted with crypt cells). To pursue these findings further we propose: 1) to define the role of NEFAs, phospholipids and phospholipases in the molecular mechanisms of sequestering calcium during its absorption by the intestine, 2) to purify the Ca2+-ATPase of L-B membrane presumed responsible for ATP-dependent Ca2+ uptake, and 3) to study the molecular mechanisms by which 1,25(OH)2D3 effects Ca2+-ATPase function by either a genomic mechanism or through a post-translational activation of the enzyme. We will also try to determine if 1,25-(OH)2D3 stimulates the synthesis or appearance of proteins in Golgi and L-B membrane important to lipid metabolism. The effect of 1,25(OH)2D3 on the mRNA for Ca2+-ATPase will be studied. Changes in these parameters as related to enterocyte differentiation will be emphasized. Since there is evidence that 1,25(OH)2D3-dependent calcium transport is, in fact, dependent on enterocyte differentiation, it seems an ideal system for increasing our understanding of differentiation and tissue organization in relationship to a specific intestinal function. Regulation of intestinal calcium transport is fundamental to calcium homeostasis. Therefore, these studies will help in understanding the pathophysiology of osteoporosis, kidney stones, and the effects of intestinal diseases on calcium absorption and calcium metabolism.