Vig P J, Pentyala S N, Chetty C S, Rajanna B, Desaiah D
Department of Neurology, University of Mississippi Medical Center, Jackson 39216.
Pharmacol Toxicol. 1994 Jul;75(1):17-22. doi: 10.1111/j.1600-0773.1994.tb00318.x.
Receptor-mediated phosphoinositide signaling pathway which generates a variety of second messengers is regulated by intracellular free Ca2+ concentrations. Since toxic metal cations like Pb2+ are known to alter Ca(2+)-dependent processes, the present study was initiated to study the effects of Pb2+ on inositol 1,4,5-trisphosphate (InsP3) and inositol 1,3,4,5-tetrakisphosphate (InsP4) receptor binding and InsP3-mediated Ca(2+)-release. Rat cerebellar membrane and microsomal fractions were incubated with various concentrations of Pb2+ (0.01-100 microM). Pb2+ significantly stimulated [3H]-InsP3 and [3H]-InsP4 receptor binding (EC50 22.7 and 13.5 microM respectively) as a function of metal concentrations. However, InsP3-mediated Ca2+ release, determined by measuring the changes in fluorescence intensity of Fura-2, was significantly inhibited by varying concentrations of Pb2+. Re-uptake of Ca2+ into the microsomes was also inhibited by Pb2+. A significant inhibition of microsomal Ca(2+)-pump by micromolar concentration of Pb2+ was also observed. ATP at 5-1000 microM concentration range inhibited [3H]-InsP3 and [3H]-InsP4 binding to the specific receptors. [3H]-InsP4 receptor binding was more sensitive to ATP inhibition as compared to [3H]-InsP3 receptor binding. Furthermore, varying concentrations of ATP also inhibited Pb(2+)-mediated increase in [3H]-InsP3 and [3H]-InsP4 receptor binding. The kinetic analysis of ATP effect on Pb(2+)-stimulated [3H]-InsP4 receptor binding revealed non-competitive type of interaction. The results of the present study suggest that Pb2+ may be increasing the binding of [3H]-InsP3 and [3H]-InsP4 to the specific receptors by modulating the conformation of the receptor sites. ATP may be playing a protective role in Pb2+ induced alteration of the receptor sites.
受体介导的磷酸肌醇信号通路可产生多种第二信使，该通路受细胞内游离钙离子浓度的调节。由于已知铅离子等有毒金属阳离子会改变依赖钙离子的过程，因此开展了本研究，以探究铅离子对肌醇1,4,5 -三磷酸（InsP3）和肌醇1,3,4,5 -四磷酸（InsP4）受体结合以及InsP3介导的钙离子释放的影响。将大鼠小脑膜和微粒体部分与不同浓度的铅离子（0.01 - 100微摩尔）一起孵育。铅离子作为金属浓度的函数，显著刺激了[3H] - InsP3和[3H] - InsP4受体结合（EC50分别为22.7和13.5微摩尔）。然而，通过测量Fura - 2荧光强度变化来确定的InsP3介导的钙离子释放，受到不同浓度铅离子的显著抑制。铅离子也抑制了钙离子重新摄取到微粒体中。还观察到微摩尔浓度的铅离子对微粒体钙离子泵有显著抑制作用。5 - 1000微摩尔浓度范围内的ATP抑制了[3H] - InsP3和[3H] - InsP4与特定受体的结合。与[3H] - InsP3受体结合相比，[3H] - InsP4受体结合对ATP抑制更敏感。此外，不同浓度的ATP也抑制了铅离子介导的[3H] - InsP3和[3H] - InsP4受体结合增加。ATP对铅离子刺激的[3H] - InsP4受体结合影响的动力学分析显示为非竞争性相互作用类型。本研究结果表明，铅离子可能通过调节受体位点的构象来增加[3H] - InsP3和[3H] - InsP4与特定受体的结合。ATP可能在铅离子诱导的受体位点改变中起保护作用。
