Koh H Y, Jacklet J W
Department of Biological Sciences, University at Albany, State University of New York, Albany, New York 12222, USA.
J Neurosci. 1999 May 15;19(10):3818-26. doi: 10.1523/JNEUROSCI.19-10-03818.1999.
Nitric oxide (NO) acts as a neurotransmitter and neuromodulator in the nervous systems of many vertebrates and invertebrates. We investigated the mechanism of NO action at an identified synapse between a mechanoafferent neuron, C2, and the serotonergic metacerebral cell (MCC) in the cerebral ganglion of the mollusc Aplysia californica. Stimulation of C2 produces a decreasing conductance, very slow EPSP in the MCC. C2 is thought to use histamine and NO as cotransmitters at this synapse, because both agents mimic the membrane responses. Now we provide evidence that treatment with NO donors stimulates soluble guanylyl cyclase (sGC) in the MCC, and as a result cGMP increases. S-Nitrosocysteine (SNC, an NO donor) and 8-bromo-cGMP (8-Br-cGMP) both induced the membrane depolarization and increase in input resistance that are characteristic of the very slow EPSP. Two inhibitors of sGC, 6-anilino-5,8-quinolinequinone (LY83583) and 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxaline-1-one (ODQ), suppressed both the very slow EPSP and the membrane responses to SNC but not the histamine membrane responses. NO-induced cGMP production was determined in the MCC using cGMP immunocytochemistry (cGMP-IR). In the presence of 3-isobutyl-1-methylxanthine (IBMX), 10 microM SNC was sufficient to induce cGMP-IR, and the staining intensity increased as the SNC dose was increased. This cGMP-IR was suppressed by ODQ in a dose-dependent manner and completely blocked by 10 microM ODQ. Histamine did not induce cGMP-IR. The results suggest that NO stimulates sGC-dependent cGMP synthesis in the MCC and that cGMP mediates the membrane responses. The cotransmitter histamine induces essentially the same membrane responses but seems to use a separate and distinct second messenger pathway.
一氧化氮（NO）在许多脊椎动物和无脊椎动物的神经系统中作为神经递质和神经调质发挥作用。我们研究了在海兔加利福尼亚海兔神经节中，机械传入神经元C2与血清素能大脑后叶细胞（MCC）之间一个已确定的突触处，NO的作用机制。刺激C2会在MCC中产生电导降低、非常缓慢的兴奋性突触后电位（EPSP）。C2被认为在此突触处使用组胺和NO作为共递质，因为这两种物质都能模拟膜反应。现在我们提供证据表明，用NO供体处理可刺激MCC中的可溶性鸟苷酸环化酶（sGC），结果导致环磷酸鸟苷（cGMP）增加。S-亚硝基半胱氨酸（SNC，一种NO供体）和8-溴-cGMP（8-Br-cGMP）都诱导了膜去极化和输入电阻增加，这是非常缓慢的EPSP的特征。sGC的两种抑制剂，6-苯胺基-5,8-喹啉醌（LY83583）和1H-[1,2,4]恶二唑并[4,3-a]喹喔啉-1-酮（ODQ），抑制了非常缓慢的EPSP以及对SNC的膜反应，但不抑制组胺的膜反应。使用cGMP免疫细胞化学（cGMP-IR）在MCC中测定了NO诱导的cGMP产生。在存在3-异丁基-1-甲基黄嘌呤（IBMX）的情况下，10微摩尔的SNC足以诱导cGMP-IR，并且随着SNC剂量增加，染色强度增加。这种cGMP-IR被ODQ以剂量依赖性方式抑制，并被10微摩尔的ODQ完全阻断。组胺未诱导cGMP-IR。结果表明，NO刺激MCC中依赖sGC的cGMP合成，并且cGMP介导膜反应。共递质组胺诱导基本相同的膜反应，但似乎使用一条单独且不同的第二信使途径。
