Endothelium-derived cyclooxygenase (COX) products regulate cerebral vascular tone in newborn pigs. Both COX-1 and COX-2 are constitutively expressed in endothelial cells from newborn pig cerebral microvessels. We investigated the role of protein phosphorylation in the regulation of COX activity. The protein tyrosine phosphatase (PTP) inhibitors phenylarsine oxide, vanadate, and benzylphosphonic acid rapidly stimulated COX activity, whereas the protein tyrosine kinase inhibitors, genistein and tyrphostins, inhibited it. Protein synthesis inhibitors did not reverse the stimulation of COX activity evoked by PTP inhibitors. Similar changes were observed in other vascular cells from newborn pigs that also express COX-1 and COX-2 (cerebral microvascular smooth muscle cells and aortic endothelial cells) but not in human umbilical vein endothelial cells or Swiss 3T3 fibroblasts that express COX-1 only. Tyrosine-phosphorylated proteins were immunodetected in endothelial cell lysates. COX-2 immunoprecipitated from 32P-loaded endothelial cells incorporated 32P that was increased by PTP inhibitors. COX-2, but not COX-1, was detected in endothelial fractions immunoprecipitated with anti-phosphotyrosine. These data indicate that tyrosine phosphorylation posttranslationally regulates COX activity in newborn pig vascular cells and that COX-2 is a substrate for phosphorylation.

Dilation of piglet pial arterioles to glutamate involves carbon monoxide (CO) produced from heme by heme oxygenase-2 (HO-2). Piglet cerebral microvessels and endothelial and smooth muscle cells grown on microcarrier beads were used to address the hypothesis that glutamate increases endothelial CO production by increasing HO-2 catalytic activity. CO was measured by gas chromatography/mass spectrometry. Glutamate increased CO production from endogenous heme by cerebral microvessels, endothelial cells, and smooth muscle cells. Glutamate increased the conversion of exogenous heme to CO. Protein tyrosine kinase inhibition blocked glutamate stimulation of CO production. Inhibition of protein tyrosine phosphatases stimulated CO production. Conversely, neither phorbol myristate acetate nor H-7 changed glutamate stimulation of CO production. The mechanism of HO-2 stimulation by glutamate appears to be independent of cytosolic Ca, because stimulation of CO production by glutamate was the same in Careplete medium, Ca-free medium with ionomycin, and Careplete medium with ionomycin. Therefore, glutamate appears to increase HO-2 catalytic activity in cerebral microvessels via a tyrosine kinase mediated pathway. heme oxygenase; cerebrovascular circulation; endothelium; vascular smooth muscle; phosphorylation; calcium CARBON MONOXIDE (CO) is an important cellular signaling molecule in the cerebral circulation. In newborn pigs, the constitutive enzyme that produces CO, heme oxygenase-2 (HO-2), has very high expression in cerebral microvessels. Of the vascular tissues examined, by far the greatest production of CO is by cerebral microvessels (19). The excitatory amino acid glutamate stimulates CO production by piglet cerebral microvessels (30). Furthermore, inhibition of HO reduces cerebral arteriolar dilation in response to glutamate and glutamatergic seizures (19,25,29). Therefore, glutamate increases activity of the HO-2 pathway, and the CO produced appears to cause subsequent dilation.In this study, we asked which vascular cells produce CO in response to glutamate and how is this production increased? Both endothelial cells and smooth muscle cells of the cerebral circulation express HO-2 (8, 21, 31) and have glutamate receptors (17,26,34). We (28) have shown that isolated cerebral vascular endothelial cells respond to glutamate by increasing CO production, but it was not known whether smooth muscle cells do so as well.Rapid elevation of CO production in response to glutamate obviates the possibility of increased expression of HO-2 or induction of HO-1. Assuming that total cellular HO-2 does not change during the experimental time course, CO production could be controlled by regulation of substrate availability to HO-2 or the effective catalytic activity of HO-2. Catalytic activity includes the specific catalytic efficiency of the enzyme, as well as intracellular localization, to optimize substrate and cofactor proximity.We used freshly isolated piglet cerebral microvessels and endothelial and smooth muscle cells in primary cu...

Carbon monoxide (CO) is produced from heme by heme oxygenase-2 (HO-2) in cerebral blood vessels. Gas chromatography-mass spectrometry was used on piglet cerebral microvessels to address the hypothesis that CO production is regulated by heme delivery and HO-2 catalytic activity. CO production appears to be substrate limited because heme and its precursor aminolevulinate increase CO production. Ionomycin also increases CO production. However, CO production from exogenous heme was the same in Ca-replete medium, Ca-free medium with ionomycin, and Ca-replete medium with ionomycin. Phorbol myristate acetate increases CO production but does not change the catalytic activity of HO-2. Also, the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine has no effect on the HO-2 catalytic activity. Protein tyrosine kinase inhibition reduces HO-2 catalytic activity. Inhibition of protein tyrosine phosphatases increased HO-2 catalytic activity. Therefore, regulation of CO production by cerebral microvessels can include changing heme availability and HO-2 catalytic activity. HO-2 catalytic activity is stimulated by tyrosine phosphorylation.

Carbon monoxide (CO) and nitric oxide (NO) can be involved in the regulation of cerebral circulation. Inhibition of production of either one of these gaseous intercellular messengers inhibits newborn pig cerebral arteriolar dilation to the excitatory amino acid glutamate. Glutamate can increase NO production. Therefore, the present study tests the hypothesis that NO, which is increased by glutamate, stimulates the production of CO by cerebral microvessels. Experiments used freshly isolated cerebral microvessels from piglets that express only heme oxygenase-2 (HO-2). CO production was measured by gas chromatography-mass spectrometry. Although inhibition of nitric oxide synthase (NOS) with N -nitro-Larginine (L-NNA) did not alter basal HO-2 catalytic activity or CO production, L-NNA blocked glutamate stimulation of HO-2 activity and CO production. Furthermore, the NO donor sodium nitroprusside mimicked the actions of glutamate on HO-2 and CO production. The action of NO appears to be via cGMP because 8-bromo-cGMP mimics and 1H-[1,2,4]oxadiazole-[4,3-a]quinoxalin-1-one (ODQ) blocks glutamate stimulation of CO production and HO-2 catalytic activity. Inhibitors of neither casein kinase nor phosphotidylinositol 3-kinase altered HO-2 catalytic activity. Conversely, inhibition of calmodulin with calmidazolium chloride blocked glutamate stimulation of CO production and reduced HO-2 catalytic activity. These data suggest that glutamate may activate NOS producing NO that leads to CO synthesis via a cGMP-dependent elevation of HO-2 catalytic activity. These results are consistent with the findings in vivo that either HO or NOS inhibition blocks cerebrovascular dilation to glutamate in piglets. heme oxygenase; guanosine 3Ј, 5Ј-cyclic monophosphate; nitric oxide synthase; glutamate BOTH CARBON MONOXIDE (CO) and nitric oxide (NO) are endogenously produced, gaseous, intercellular messengers that can be involved in regulation of cerebral circulation. In neonatal pigs, CO regulation and modulation are involved in cerebrovascular circulatory control in response to neuronal activity, hypoxia, and changing blood pressure (12,18,26,41). Whereas the contributions of NO to cerebral blood flow regulation increase with age (40, 47), NO is important in the newborn as a permissive factor enabling vascular responses to CO (15). In the piglet cerebrovascular circulation, glutamateinduced pial arteriolar dilation can be blocked by either inhibiting nitric oxide synthase (NOS) (14, 24), which produces NO, or heme oxygenase (HO) (18, 30), which produces CO. One possible explanation for these apparently conflicting data is that one gaseous messenger is necessary to allow dilation to the other. Indeed, as noted above, such a permissive contribution of NO to CO-induced dilation has been described. Another possibility is that glutamate receptor activation increases the production of one of the two gases and that gas in turn increases the production of the other, which is the final mediator of the dilatory response.CO has been reported to directly a...

In newborn pig pial arterioles and cocultures of cerebral microvascular endothelial and smooth muscle cells, hypercapnia increases cAMP. In the intact cerebral circulation, both the increase in cAMP and the accompanying vasodilation require the presence of PGI(2). Using piglet cerebral microvascular smooth muscle in primary culture, we addressed the hypothesis that, in the presence of PGI(2), hypercapnia-induced changes in extracellular pH cause increases in cAMP. The stable PGI(2)-receptor agonist iloprost did increase production of cAMP in response to combined extracellular pH and pH(i) (11 +/- 6 vs. 32 +/- 10% in the absence and presence of 10(-10) M iloprost, respectively). However, there was no positive dose-response relationship between iloprost concentration and stimulation of cAMP production by acidosis (e.g., 58 +/- 9 vs. 41 +/- 5% in the presence of 10(-12) and 10(-9) M iloprost, respectively). Rapid decreases in pH(i) stimulate the cAMP production. Decreases in extracellular pH do not appear to contribute further. The G protein inhibitor pertussis toxin did not augment cAMP production in response to decreasing pH(i). We conclude that PGI(2) receptor activation permits another mechanism to enhance cAMP generation in response to intracellular, but not extracellular, acidosis and that the mechanism of the permissive effect of PGI(2) does not involve inhibition of a pertussis toxin-sensitive G protein.