Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The localization of histamine receptors and their classes on the microvascular endothelium was assessed by using the electron-opaque conjugate histamine-ferritin (HF). In order to further check the specific binding of this conjugate, two compounds chemically similar to histamine but biologically inactive, tele-methylhistamine (t-MH) and 4-pyridylethylamine (PEA), and a specific H2 histamine receptor antagonist, SK&F 93479, were used. Glutaraldehyde-activated ferritin was covalently coupled with either histamine, as a biologically active HF conjugate, or with tele-methylhistamine, as a biologically inactive conjugate tele-methylhistamine-ferritin (t-MHF). The purity of the conjugates was determined by thin-layer chromatography. The HF conjugate (25 mg protein/100 g body weight) was perfused into RAP mice and bipolar microvascular fields of the diaphragm were fixed and processed for electron microscopy. The HF conjugate decorated restricted domains of the luminal aspect of the microvascular endothelium. The specific density of HF binding, recorded as the average number of binding sites per square micrometer of the luminal endothelial surface, was relatively high in venules (18.46 +/- 5.73) and lower in arterioles (12.89 +/- 6.13) and capillaries (9.51 +/- 4.20). The binding specificity of the HF conjugate was assessed through six groups of experiments: perfusion before HF conjugate with either histamine, tele-methylhistamine or 4-pyridylethylamine, perfusion with t-MHF conjugate only, or administration before t-MHF conjugate of either histamine or tele-methylhistamine. The statistical significance of the data was analyzed by using the "F" distribution test and the "Wilcoxon-Mann-Whitney rank-sum test". Both tele-methylhistamine and 4-pyridylethylamine as well as histamine, showed a higher competition on arterioles and venules than on capillaries. Neither tele-methylhistamine nor histamine inhibited the binding of t-MHF conjugate on the endothelium. Experiments using SK&F 93479 as a very potent H2 histamine receptor antagonist perfused before HF administration, suggested the existence of H2 histamine receptors at a higher concentration in venules (47.03%) and arterioles (38.80%) than in capillaries (14.16%). These findings demonstrate that HF conjugate binds specifically to the histamine receptors of microvascular endothelium, which are characteristically frequent and predominantly of H2 type in venules.
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PMID:Further evidence for the distribution and nature of histamine receptors on microvascular endothelium. 243 46

Mast cells isolated from the peritoneal fluid of Wistar rats were purified by centrifugation on Percoll gradient with a yield of 2x10(6) cells/ml. Cell morphology was well preserved as shown by light and electron microscopy. The mast cells capacity to bind histamine was assayed using either [3H]-histamine or histamine-ferritin conjugate as electron-opaque probe for electron microscopic examination. The [3H]-histamine binding performed at 4 degrees C in Ca2+-free phosphate-buffered saline pH 7.3 completed within 30 min was found to be specific, with an IC50 value of 0.72 +/- 0.23 nM. The data analyses by Scatchard and Hill's representations showed a KD of 0.60 +/- 0.24 nM and Bmax of 4.9 +/- 1.2 pM/10(6) cells suggesting that on mast cells the histamine receptors are restricted to the plasma membrane. According to Hill's analysis neither positive nor negative cooperativity (n = 1.06) appeared to be involved in the specific histamine-receptor binding. Competition experiments with 4-methylhistamine and SK&F 93479, revealed that mast cells express H2-histamine receptors. At electron microscopic level, the histamine-ferritin conjugate interstitially injected in the hamster cheek pouch was localized on the mast cell membrane.
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PMID:Histamine receptor on mast cells. 325 80

Histamine covalently bound to glutaraldehyde-activated ferritin was prepared as either monomers or as small aggregates of approximately 0.05 to 0.15 micrometer Diam, suitable for electron microscopic detection of histamine cellular binding sites. The histamine-ferritin conjugates (MF) maintain the histamine capability to induce the opening of endothelial junctions in venules. To investigate the distribution of histamine receptors in the vascular endothelium, monomers or aggregates of MF were perfused in situ (mice), and various vascular beds, particularly that of the diaphragm, were fixed and processed for electron microscopy. The conjugate was preferentially bound on restricted areas of luminal endothelial cell plasmalemma especially in regions rich in filaments, and near the junctions between endothelial cells. The density of histamine binding sites was characteristically high in venules; it occurred to a much lesser extent in arterioles, veins, and muscular arteries whereas capillaries and aorta showed the lowest values. A similar distribution was obtained after perfusion of H1 or H2 receptor agonists coupled to ferritin (2-pyridylethylamine-ferritin [PF], or 4-methylhistamine-ferritin [MF], respectively). The binding specificity was assessed through control experiments with either native or activated ferritin or by competition with histamine. The findings suggest that histamine receptors are largely represented in the cell membrane of the vascular endothelium, particularly in venules. Experiments using specific H1 and H2 receptor agonists (PF and MF) and antagonists (mepyramine and cimetidine) indicate that the venular endothelium contains mainly H2 receptors.
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PMID:Histamine receptors of the microvascular endothelium revealed in situ with a histamine-ferritin conjugate: characteristic high-affinity binding sites in venules. 720 74