Role of carbon monoxide derived from heme-oxygenase 2 on the regulation of neural function

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As the first part of the project, we propose a novel hypothesis to explain the long standing controversy concerning the contribution of diatoimic gas molecules, namely nitric oxide(NO) and carbon monoxide(CO), to the regulation of soluble guanylate cyclase(sGC) in vivo. We suggest that the effect of CO on modulating sGC activity is not static but dynamic in that low tissue availability of NO makes CO a stimulatory modulator of sGC while high tissue availability of NO makes CO an inhibitory modulator. Our study was designed to evaluate the hypothesis that NO is the dominant activator of sGC but endogenous CO plays a role on refining the NO-mediated regulation of sGC function. We chose the rat retina as an experimental system because its well-defined anatomical layers consisting of specific cell types enabled us to examine spatial relationships between NO- or CO-generating enzyme and its receptor protein, sGC.Our findings provide some of the first direct evidence that sGC is present in M … More uller's glia cells(MGCs) and on-type bipolar cells and that its activity is controlled by locally produced NO and CO. Furthermore, mechanisms for sGC regulation by these gases appear to be executed not uniformly but site-specifically over the different layers of retina. Under conditions where house-keeping levels of CO were suppressed by zinc protophophyrin IX(ZnPP), all retinal cell layers homogeneously exhibited NO-dependent activation of sGC to the greatest extent. On the other hand, under NO-suppressing conditions, inhibition of endogenous CO abrogated the sGC activation in a layer-specific manner at the optic fiber layer and external limiting membrane. These results suggest that endogenous CO plays a role in fine-tuning dynamic ranges of the NO-dependent regulation of sGC function by suppressing the maximum response as well as by modestly elevating the minimum response in particular layers of retina.As the second part of the project, we provide the first direct evidence that CO produced by HO can attenuate vasodilatory responses of pial arterioles by interfering with the NO production in the adult rat. In this study, the physiological relevance of CO production in cerebral microcirculation is supported by the results of two independent experimental approaches : measurement of pial arteriolar diameter under conditions where endogenous CO or NO production was varied, and direct detection of NO production in situ using the fluoroprobe under normal and CO-suppressed conditions. Although exact cell types that exhibit the NO^+-sensitive fluorescence are yet to be identified, the use of the confocal system to quantify fluorescence intensity together with the immunohistochemical detection of NO-producing enzymes provides spatial and temporal information of NO production of cerebral microcirculation in situ for the first time.0 Less