Takeuchi K, Guggino S E
Department of Medicine, The Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
J Biol Chem. 1996 Dec 27;271(52):33335-43. doi: 10.1074/jbc.271.52.33335.
Calcium influx via L-type calcium channels in osteoblast cells causes a rapid (in seconds) elevation in intracellular calcium initiated by plasma membrane receptors for 1alpha, 25-dihydroxyvitamin D3 (1alpha,25-D3). 24R,25-Dihydroxyvitamin D3 (24,25-D3) alone, in concentrations up to 200 nM, does not cause potentiation of calcium currents in osteoblasts, but it does inhibit the current potentiation by 1alpha,25-D3. To determine how various steroids interact in their potentiation of calcium channels, the action of vitamin D3 analogues and testosterone with calcium channels in the rat osteoblast-like cell line ROS 17/2.8 was investigated. Bath additions of both 1alpha,25-D3 and testosterone at doses below K1/2 (the dose causing 50% left shift in the current-voltage relationship) are additive in their ability to potentiate calcium channels. When 1alpha,25-D3 and testosterone are added together at concentrations that would cause a maximal shift in the current-voltage relationship by each agent alone (Vmax), the effect of these steroids is not additive. Taken together these data suggest one population of calcium channels is activated by 1alpha, 25-D3 or testosterone. The shift in the current-voltage relationship caused by 1alpha,25-D3 is reduced by 1beta,25-dihydroxyvitamin D3 (1beta,25-D3), an agent which is thought to act specifically on the plasma membrane receptor for 1alpha,25-D3, but the potentiation caused by testosterone is not blocked by 1beta,25-D3. However, 24, 25-D3 inhibits the left shift in the peak current-voltage relationship mediated by either 1alpha,25-D3 and testosterone. This result implies that 1) 1beta,25-D3 directly displaces 1alpha,25-D3 but not testosterone from its plasma membrane receptor, and 2) the rapid (in seconds) stimulatory effects of 1alpha,25-D3 and testosterone on calcium channels are mediated by separate plasma membrane receptors for testosterone and 1alpha,25-D3, which are blocked by another receptor for 24,25-D3. The interaction of these three receptors with L-type calcium channels is pertussis toxin-sensitive.
成骨细胞中通过L型钙通道的钙内流会导致细胞内钙迅速（数秒内）升高，这是由1α,25 - 二羟基维生素D3（1α,25 - D3）的质膜受体引发的。单独使用浓度高达200 nM的24R,25 - 二羟基维生素D3（24,25 - D3）不会增强成骨细胞中的钙电流，但它确实会抑制1α,25 - D3对电流的增强作用。为了确定各种类固醇在增强钙通道方面是如何相互作用的，研究了维生素D3类似物和睾酮在大鼠成骨样细胞系ROS 17/2.8中与钙通道的作用。以低于K1/2（使电流 - 电压关系向左偏移50%的剂量）的剂量向浴液中添加1α,25 - D3和睾酮，它们增强钙通道的能力是相加的。当以单独使用时每种试剂会使电流 - 电压关系产生最大偏移（Vmax）的浓度将1α,25 - D3和睾酮一起添加时，这些类固醇的作用不是相加的。综合这些数据表明，一类钙通道可被1α,25 - D3或睾酮激活。1β,25 - 二羟基维生素D3（1β,25 - D3）可降低1α,25 - D3引起的电流 - 电压关系的偏移，1β,25 - D3被认为特异性作用于1α,25 - D3的质膜受体，但睾酮引起的增强作用不受1β,25 - D3的阻断。然而，24,25 - D3会抑制由1α,25 - D3和睾酮介导的峰值电流 - 电压关系的左移。这一结果意味着：1）1β,25 - D3直接将1α,25 - D3而非睾酮从其质膜受体上置换下来；2）1α,25 - D3和睾酮对钙通道的快速（数秒内）刺激作用是由睾酮和1α,25 - D3各自独立的质膜受体介导的，而这些受体被另一种24,25 - D3受体阻断。这三种受体与L型钙通道的相互作用对百日咳毒素敏感。
