Taft J L, Shaw M, Danks J A, Prince R L, Larkins R G
Endocrinology. 1986 Sep;119(3):1131-6. doi: 10.1210/endo-119-3-1131.
The conversion of circulating 25-hydroxyvitamin D3 (25OHD3) to its active metabolite 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in the renal tubule mitochondrion by the enzyme 25OHD3-1 alpha-hydroxylase is closely regulated in vivo according to the physiological need for calcium and phosphorus. The mechanism by which this regulation is achieved at the cellular level has not been clarified, although a number of lines of evidence suggest that calcium ions (Ca2+) are involved. This study was designed to determine whether calmodulin, the ubiquitous cell protein that binds and mediates many of the regulatory functions of Ca2+, plays a role in the regulation of renal vitamin D metabolism. The calmodulin antagonists trifluoperazine (TFP), Janssen R24571, and the naphthalene sulfonamides W5 and W7 inhibited conversion of 25OHD3 to 1,25-(OH)2D3 by isolated renal tubules from vitamin D-deficient chicks in a dose-dependent manner (ED50: TFP, 12 mumol/liter; R24571, 10 mumol/liter; W7, 30 mumol/liter; W5, 75 mumol/liter). TFP did not inhibit production of the alternative metabolite 24,25-(OH)2D3 by chick renal tubules. In a similar manner, TFP, W7, and W5 inhibited conversion of 25OHD3 to 1,25-(OH)2D3 by isolated energized chick renal mitochondria, with no detrimental effect on mitochondrial respiratory indices. Bovine brain calmodulin in a concentration of 1 X 10(-7) mol/liter enhanced 1,25-(OH)2D3 production by isolated chick renal mitochondria in Ca2+ -containing medium, but not in the absence of Ca2+. Preincubating mitochondria with anticalmodulin antiserum resulted in decreased conversion of 25OHD3 to 1,25-(OH)2D3, an effect that was prevented by exogenous calmodulin. These data support the notion of a role for calmodulin in the Ca2+ -mediated control of renal 1 alpha-hydroxylase activity.
在肾小管线粒体中，通过25羟维生素D3 - 1α - 羟化酶将循环中的25 - 羟基维生素D3（25OHD3）转化为其活性代谢产物1,25 - 二羟基维生素D3 [1,25 - (OH)2D3]，在体内会根据钙和磷的生理需求受到密切调控。尽管有许多证据表明钙离子（Ca2+）参与其中，但在细胞水平实现这种调控的机制尚未阐明。本研究旨在确定钙调蛋白（这种普遍存在的细胞蛋白能结合并介导Ca2+的许多调节功能）是否在肾脏维生素D代谢的调节中发挥作用。钙调蛋白拮抗剂三氟拉嗪（TFP）、扬森R24571以及萘磺酰胺W5和W7以剂量依赖性方式抑制了维生素D缺乏雏鸡分离的肾小管将25OHD3转化为1,25 - (OH)2D3（半数有效剂量：TFP为12 μmol/升；R24571为10 μmol/升；W7为30 μmol/升；W5为75 μmol/升）。TFP并不抑制雏鸡肾小管产生替代代谢产物24,25 - (OH)2D3。同样，TFP、W7和W5抑制了分离的有活力的雏鸡肾脏线粒体将25OHD3转化为1,25 - (OH)2D3，且对线粒体呼吸指标没有不利影响。浓度为1×10(-7) mol/升的牛脑钙调蛋白在含Ca2+的培养基中增强了分离的雏鸡肾脏线粒体产生1,25 - (OH)2D3的能力，但在无Ca2+的情况下则不然。用抗钙调蛋白抗血清对线粒体进行预孵育会导致25OHD3向1,25 - (OH)2D3的转化减少，而外源性钙调蛋白可阻止这种效应。这些数据支持了钙调蛋白在Ca2+介导的肾脏1α - 羟化酶活性控制中发挥作用的观点。
