LEAD INDUCED CHANGES IN NITRIC OXIDE SIGNAL TRANSDUCTION

铅（Pb2+）引起的神经系统疾病的潜在机制与许多神经递质系统功能的破坏相关，导致神经传递受损。然而，认知功能障碍与Pb2+暴露之间的关系尚不清楚。Pb2+暴露改变Ca2+稳态，在神经元发育和可塑性中起关键作用。最近的证据表明：(1)一氧化氮合酶（NOS）活性在突触可塑性中起关键作用；(2)一氧化氮（NO）介导的一氧化碳（CO）和cGMP生成以及cGMP依赖性蛋白激酶（PKG）活性可以通过环ADP核糖（cADPR）和肌醇1,4,5-三磷酸（InsP3）门控的Ca2+通道改变Ca2+稳态。Pb2+在体外可降低脑内NOS活性，可能是Pb(2+)-诱导的NOS活性和NO水平的降低导致NO介导的血红素加氧酶（HO-2）生成CO、可溶性鸟苷酸环化酶（sGC）生成cGMP和细胞内Ca2+动员的变化。我们的假设是，Pb2+暴露降低NOS活性和NO水平，从而通过CO和cGMP调节NO介导的信号转导，以及在中枢神经系统发育过程中起关键作用的Ca2+稳态，从而导致认知功能障碍。为了验证上述假设，本研究提出评估Pb2+暴露对：(1)NOS和HO-2活性，(2)NO和CO的靶标sGC活性，(3)cGMP水平，(4)dgmp依赖性蛋白激酶（PKG）活性，(5)cADPR和InsP3水平，以及(6)cADPR和InsP3依赖性Ca2+释放及其通过PKG介导的磷酸化调节。

The underlying mechanism(s) of neurological disorders caused by lead (Pb2+) have been correlated to the disruption of functioning of a number of neurotransmitter systems leading to impairment of neural transmission. However, the relationship between cognitive dysfunction and Pb2+ exposure is still unclear. Pb2+ exposure alters Ca2+ homeostasis which plays a critical role in neuronal development and plasticity. Recent evidence suggests that (1) nitric oxide synthase (NOS) activity plays a pivotal role in synaptic plasticity, and (2) nitric oxide (NO)-mediated carbon monoxide (CO) and cGMP generation and cGMP-dependent protein kinase (PKG) activity can alter Ca2+ homeostasis via cyclic ADP ribose (cADPR)- and inositol 1,4,5-triphosphate (InsP3)-gated Ca2+ channels. Pb2+, in vitro, decreases NOS activity of brain, and it is likely that Pb(2+)- induced decrease in NOS activity and NO levels leads to changes in NO-mediated CO generation by heme oxygenase (HO-2), cGMP generation by soluble guanylate cyclase (sGC), and mobilization of intracellular Ca2+. The hypothesis to be tested is that Pb2+ exposure decreases NOS activity and NO levels resulting in the modulation of NO-mediated signal transduction via CO and cGMP, and Ca2+ homeostasis, which play a crucial role during the development of the central nervous system, leading to cognitive dysfunction. To test the above hypothesis, the present study is proposed to assess the effect of Pb2+ exposure on: (1) NOS and HO-2 activity, (2) sGC activity, a target for NO and CO, (3) cGMP levels, (4) dGMP-dependent protein kinase (PKG) activity, (5) cADPR and InsP3 levels, and (6) cADPR- and InsP3-dependent Ca2+ release and their modulation by PKG- mediated phosphorylation.