Reinhart P H, Taylor W M, Bygrave F L
Biochem J. 1984 May 15;220(1):43-50. doi: 10.1042/bj2200043.
The effect of alpha-adrenergic agonists on Ca2+ fluxes was examined in the perfused rat liver by using a combination of Ca2+-electrode and 45Ca2+-uptake techniques. We showed that net Ca2+ fluxes can be described by the activities of separate Ca2+-uptake and Ca2+-efflux components, and that alpha-adrenergic agonists modulate the activity of both components in a time-dependent manner. Under resting conditions, Ca2+-uptake and -efflux activities are balanced, resulting in Ca2+ cycling across the plasma membrane. The alpha-adrenergic agonists vasopressin and angiotensin, but not glucagon, stimulate the rate of both Ca2+ efflux and Ca2+ uptake. During the first 2-3 min of alpha-agonist administration the effect on the efflux component is the greater, the net effect being efflux of Ca2+ from the cell. After 3-4 min of phenylephrine treatment, net Ca2+ movements are essentially complete, however, the rate of Ca2+ cycling is significantly increased. After removal of the alpha-agonist a large stimulation of the rate of Ca2+ uptake leads to the net accumulation of Ca2+ by the cell. The potential role of these Ca2+ flux changes in the expression of alpha-adrenergic-agonist-mediated effects is discussed.
采用钙离子电极和45Ca2+摄取技术相结合的方法，在灌注大鼠肝脏中研究了α-肾上腺素能激动剂对Ca2+通量的影响。我们发现，净Ca2+通量可以用单独的Ca2+摄取和Ca2+外流成分的活性来描述，并且α-肾上腺素能激动剂以时间依赖性方式调节这两种成分的活性。在静息条件下，Ca2+摄取和外流活性是平衡的，导致Ca2+在质膜上循环。α-肾上腺素能激动剂血管加压素和血管紧张素（而非胰高血糖素）刺激Ca2+外流和Ca2+摄取的速率。在给予α-激动剂的最初2-3分钟内，对外流成分的影响更大，净效应是Ca2+从细胞中流出。在去氧肾上腺素处理3-4分钟后，净Ca2+移动基本完成，然而，Ca2+循环速率显著增加。去除α-激动剂后，Ca2+摄取速率的大幅刺激导致细胞净积累Ca2+。讨论了这些Ca2+通量变化在α-肾上腺素能激动剂介导的效应表达中的潜在作用。
