Expression of histamine receptors (H(1), H(2), and H(3)) in the rabbit endolymphatic sac: an immunohistochemical study

OBJECTIVE

The endolymphatic sac (ES) is part of the membranous labyrinth of the inner ear. Its central role in immunologic activity within the inner ear has been confirmed by numerous studies. The aim of this study was to investigate the expression of histamine receptors (H(1), H(2), H(3)) in the rabbit ES.

METHODS

A total of 10 healthy male New Zealand white rabbits weighing 2 to 3 kg were used in the experiments. For immunohistochemical studies, immunostaining was performed according to the avidin-biotin-peroxidase complex technique.

RESULTS

Serial sections of the ES of rabbits revealed the presence of H(1), H(2), and H(3) receptor immunoreactivity. Immunoreactive cells for all H(1), H(2), and H(3) were found in the epithelial and subepithelial layers of the duct and the proximal ES. In conclusion, this study showed the immunohistochemical localization of H(1), H(2), and H(3) receptors in the ES of rabbits. These receptors may be important in the homeostasis of the inner ear. In addition, they may be target receptors in the medical treatment of inner ear disorders such as endolymphatic hydrops.

Histamine improves antigen uptake and cross-presentation by dendritic cells

Previous studies have shown that histamine is able to modulate the function of dendritic cells (DCs). Histamine seems to be required for the normal differentiation of DCs. Moreover, it is capable of stimulating the chemotaxis of immature DCs and of promoting the differentiation of T CD4+ cells into a Th2 profile. In this study, we analyzed whether histamine was able to modulate endocytosis and cross-presentation mediated by immature DCs. Our results show that both functions are stimulated by histamine. Endocytosis of soluble HRP and FITC-OVA and cross-presentation of soluble OVA were markedly increased by histamine. Interestingly, stimulation of endocytosis and cross-presentation appeared to be mediated through different histamine receptors. In fact, the enhancement of endocytosis was prevented by the histamine2 receptor (H2R) antagonist cimetidine, whereas the stimulation of cross-presentation was prevented by the H3R/H4R antagonist thioperamide. Of note, contrasting with the observations made with soluble Ags, we found that histamine did not increase either the uptake of OVA-attached to latex beads, or the cross-presentation of OVA immobilized on latex beads. This suggests that the ability of histamine to increase endocytosis and cross-presentation is dependent on the Ag form and/or the mechanisms through which the Ag is internalized by DCs. Our results support that histamine may favor cross-presentation of soluble allergens by DCs enabling the activation of allergen-specific T CD8+ cells, which appears to play an important role in the development of allergic responses in the airway.

Heterologous up-regulation of the histamine H1 receptor by M3 muscarinic receptor-mediated activation of H1-receptor gene transcription

Histamine H(1) receptor (H1R) level varies under various pathological conditions, and these changes may be responsible for some pathogenesis, such as allergic rhinitis. Previously, we showed that H1R was heterologously down-regulated (through degradation of H1R) by prolonged stimulation with muscarinic M(3) receptor (M3R) in Chinese hamster ovary (CHO) cells stably expressing H1R and M3R. However, this cell was inadequate for studying the effects on H1R gene regulation, because the cell expresses H1R, which is under the control of the SV40 promoter. Therefore, in this study, we have investigated the possible role of M3R stimulation in the H1R gene transcription and H1R mRNA stability by using U373 astrocytoma cells that express endogenous H1R and transfected M3R. Stimulation of M3R significantly increased H1R promoter activity and H1R mRNA level without alteration in H1R mRNA stability. The H1R level was also up-regulated by M3R activation (150% of control by treatment with carbachol for 24 h). These M3R-mediated events were almost completely blocked by the protein kinase C (PKC) inhibitor, Ro 31-8220, suggesting the involvement of PKC. These results indicated that M3R was involved in the up-regulation of H1R by activating H1R gene transcription through a PKC-dependent process.

Ligation of Toll-like receptor 3 differentially regulates M2 and M3 muscarinic receptor expression and function in human airway smooth muscle cells

BACKGROUND

Viral infection causes asthma exacerbations and airway hyperreactivity. Toll-like receptor 3 (TLR3) recognizes double-stranded RNA (dsRNA) of viral or synthetic origin in a fashion different from protein kinase R (PKR). The aim of this study was to examine the expression and function of TLR3 in human airway smooth muscle (ASM) cells.

METHODS

Expression of TLR3 and muscarinic receptor (MR), histamine receptor (HR), and cysteinyl leukotriene receptor (CysLTR) subtypes was analyzed by quantitative real-time PCR, flow cytometry, or Western blotting. It was assessed whether ASM cells respond to polyinosinic-polycytidylic acid (poly I:C), a synthetic analog of dsRNA, with alterations in M2R, M3R, H1R, and CysLT1R expression. The function of these subtypes was evaluated by cholinergic regulation of forskolin-stimulated cyclic AMP accumulation or by mobilization of intracellular calcium upon stimulation.

RESULTS

ASM cells expressed TLR3 and PKR, and intracellular TLR3 expression was demonstrated. Poly I:C caused decreased M2R and increased M3R expression, without affecting H1R and CysLT1R expression. Poly I:C-treated cells showed decreased cholinergic inhibition of forskolin-stimulated cyclic AMP accumulation and enhanced calcium flux in response to acetylcholine, but not to histamine and LTD4. These modulating effects of poly I:C were reversed by chloroquine, but not by 2-aminopurine.

CONCLUSIONS

The data indicate that poly I:C internalized by ASM cells differentially regulates M2R and M3R expression and function by interacting with TLR3 rather than with PKR, suggesting that these changes may contribute to airway hyperreactivity.

Histamine H1 and H2 receptors but not H4 receptors are upregulated during bone marrow regeneration

The role of histamine receptors in radiation-induced bone marrow (BM) regeneration was investigated with aspects of functional genomics. H1R and H2R mRNA expression increased during regeneration in both histidine decarboxylase knockout (HDC-/-) and wild type (HDC+/+) mice, though to a lesser extent in HDC-/- mice. H4R mRNA expression was downregulated in both groups. Mainly CD34+ cells were responsible for the elevation of intracellular histamine and HDC content in HDC+/+ BM cell populations. The differential changes in the expression of its receptors, and also its elevated levels in hematopoietic progenitors support the regulatory role of histamine in BM regeneration, that could be further explored by future gene expression studies.

Localized expression of histamine H1 receptors in syncytiotrophoblast cells of human placenta

The previous Northern blot analysis and in situ hybridization studies showed that histamine H1-receptor (H1R) mRNA is expressed in human placenta and suggested that H(1)R plays some roles in the function of placenta in pregnancy. To investigate further, it is essential to show the precise location of H1R in the placenta. In the present study, we investigated H1R expression in human placenta by radioligand binding assay and immunohistochemical study using an antibody against human H1R. Placentas were obtained from normal uncomplicated deliveries. Membranes prepared from the tissue exhibited saturable [3H]mepyramine binding (K(d) = 4.0 +/- 0.6 nM and B(max) = 91.4 +/- 4.9 fmol/mg of protein). Stereoisomers of chlorpheniramine inhibited [(3)H]mepyramine binding; d-chlorpheniramine inhibited more potently than l-chlorpheniramine, K(i) values being 1.1 +/- 0.4 and 270 +/- 170 nM, respectively. The placenta tissues were positively immunostained with anti-H1R antibody only in the region of the syncytiotrophoblast of chorionic villus. The tissues were double stained with anti-H1R antibody and an antibody against human chorionic gonadotoropin (hCG) that is solely expressed in placental syncytiotrophoblast cells. The results showed that H1R and hCG were expressed on the same cells, that is, syncytiotrophoblast cells. These results indicate that H1Rs are specifically expressed in syncytiotrophoblast cells of human placenta organ.

Granulocyte Macrophage–Colony Stimulating Factor Increases the Expression of Histamine and Histamine Receptors in Monocytes/Macrophages in Relation to Arteriosclerosis

OBJECTIVE

To study the effect of granulocyte macrophage-colony-stimulating factor (GM-CSF) on histamine metabolism in arteriosclerosis, the expression of histidine decarboxylase (HDC; histamine-producing enzyme), histamine receptors 1 and 2 (HH1R and HH2R), and GM-CSF was investigated in human and mouse arteriosclerotic carotid arteries. Furthermore, the molecular mechanisms of GM-CSF-induced HDC and HH1R expression in monocytic U937 cells were investigated.

METHODS AND RESULTS

Immunohistochemistry showed that atherosclerotic human coronary and mouse ligated carotid arteries contained HDC-expressing macrophages. Gene expression of HDC, HH1R, HH2R, and GM-CSF was also detected in the lesions. In U937 cells, GM-CSF enhanced histamine secretion and gene expression of HDC and HH1R. A promoter assay showed that GM-CSF enhanced gene transcription of HDC and HH1R but not HH2R.

CONCLUSIONS

The present results indicate that HDC and HHR are expressed in arteriosclerotic lesion, and that GM-CSF induces HDC and HH1R expression in monocytes. Locally produced histamine might participate in atherogenesis by affecting the expression of atherosclerosis-related genes in monocytes and smooth muscle cells. The presence of histamine-producing macrophages and gene expression of histamine receptors and GM-CSF was demonstrated in arteriosclerotic lesions. In monocytic U937 cells, GM-CSF upregulated the expression of histamine and HH1R. Coordinated expression of histamine and its receptors by GM-CSF would participate in atherogenesis by affecting monocytic and SMC gene expression.

Retinoic acid enhances histamine content and H1 receptor expression in human neuroblastoma cell line Paju

BACKGROUND

A human neuroblastoma cell line (Paju) was induced by retinoic acid (RA) to differentiate into neuron-like cells.

MATERIALS AND METHODS

We studied the expression and the possible role of histamine receptors H1 and H2 in retinoic-acid mediated differentiation by semiquantitative RT-PCR. We studied the effect of exogeneously added RA on the morphological change of the human neuroblastoma cell line and the differentiation was followed by vimentine, glial fibrillary acidic protein (GFAP) and neurofilament (NF) immunostaining. We monitored the change of the histidine decarboxylase (HDC) expression and the histamine content during the RA treatment by immunoblot and flow cytometry methods.

RESULTS

Our data showed that H1 and H2 histamine receptors are present on Paju cells. Ten nM RA markedly increased the H1 receptor expression of these cells, while the H2 expression was unchanged.

CONCLUSION

In the RA-treated Paju cells, the histamine content increased compared to the untreated cells, suggesting that neuroblastoma-derived histamine is involved in the regulation of RA-induced in vitro differentiation by H1 receptors.

Inhibition of histamine H1 receptor downregulation by KT5823, a protein kinase G inhibitor

The role of various protein kinases in the downregulation of histamine H(1) receptors was studied by using their inhibitors and activators. Human histamine H(1) receptors (H(1)Rs) expressed in CHO cells were downregulated by histamine in a dose- and time-dependent manner, and this downregulation continued to increase over a 24-h period. KT5823, an inhibitor of protein kinase G, remarkably but not completely reversed the histamine-induced H(1)R downregulation over 24 h. HA1004, another inhibitor of protein kinase G, showed a similar inhibitory effect. However, both 8-Br-cGMP and 8-pCPT-cGMP, membrane-permeable analogues of cGMP, did not show any effects on H(1)R downregulation in the absence or presence of histamine. Ro 31-8220, an inhibitor of protein kinase C (PKC), did not affect histamine-induced downregulation of H(1)R; nor did phorbol 12-myristate 13-acetate, a PKC-activating phorbol ester. Similarly, histamine-induced downregulation of H(1)R was unaffected by either H-89, an inhibitor of protein kinase A, or 8-Br-cAMP, a membrane-permeable analogue of cAMP.

Hemodynamic significance of histamine synthesis and histamine H1- and H2-receptor gene expression during endotoxemia

The hypothesis that endotoxemia may modify histamine synthesis or histamine receptor expression and that these changes may contribute to cardiovascular dysfunction was tested in rabbits which were rendered endotoxemic by lipopolysaccharide (LPS; 100 micro g/kg, i.v.). The plasma histamine concentration was elevated shortly after LPS, remaining elevated (a 50-fold increase) over the experimental period of 6 h. The sustained increase in plasma histamine was associated with a time-dependent increase in expression of histidine decarboxylase (HDC) in different tissues including atrium, as determined by Western blot analysis. The H(1)-receptor antagonist diphenhydramine significantly shortened the duration of the initial hypotension and the H(2)-receptor antagonist ranitidine greatly suppressed the lasting tachycardia following LPS injection. Northern blot analysis showed that LPS dramatically induced gene expressions of histamine H(1)- and H(2)-receptors in cardiac tissues. In right atrium isolated from the septic animal, the positive chronotropic effect of histamine was significantly diminished. This was possibly due to a marked reduction in G(s)(alpha) protein expression, indicating the impaired H(2)-receptor cellular signaling. In conclusion, LPS-induced endotoxemia causes prominent increases in production of histamine through induction of HDC and in gene expression of histamine receptors. We suggest that overproduction of histamine may be partly responsible for the hemodynamic alterations of endotoxemia.

Elevated nasal mucosal G protein levels and histamine receptor affinity in a guinea pig model of nasal hyperresponsiveness

BACKGROUND

Nasal hyperresponsiveness is a common feature of allergic rhinitis, but the underlying mechanisms have yet to be elucidated. The effects of repeated antigen inhalation on the characteristics of histamine H(1) receptors and expression levels of heterotrimeric guanosine 5'-triphosphate-binding proteins in nasal mucosa were investigated to understand the mechanisms of the pathogenesis of nasal hyperresponsiveness in allergic rhinitis.

METHODS

Male Hartley guinea pigs were sensitized by the inhalation of dinitrophenylated ovalbumin antigen (10 mg of protein/ml) and repeatedly challenged by inhaling aerosolized dinitrophenylated ovalbumin antigen for 3 weeks. Twenty-four hours after the last antigen inhalation, in vivo nasal responsiveness to histamine was measured. [(3)H]Mepyramine binding assays and immunoblotting for alpha subunits of the G(q) protein were also performed using membrane preparations of isolated nasal mucosae.

RESULTS

The histamine-induced increase in intranasal pressure was significantly augmented after repeated antigen challenge, indicating that nasal hyperresponsiveness was achieved. In saturation binding studies, no significant change was observed in the density and antagonist affinity of H(1) receptors in the hyperresponsive animals. On the other hand, the affinity of histamine for high-affinity agonist binding sites in the hyperresponsive group, measured by histamine competition binding studies, was much greater than that in control animals, and these results were affected by guanosine 5'-O-(3-thiotriphosphate) in both groups. Moreover, Galpha(q) levels in nasal mucosal homogenates were significantly increased after repeated antigen challenge.

CONCLUSIONS

Elevated G protein levels in nasal mucosa might induce an increased binding affinity of histamine to its receptors, resulting in an augmented nasal response to histamine, that is, nasal hyperresponsiveness, in guinea pigs.

Localisation of mRNAs for diamine oxidase and histamine receptors H1 and H2, at the feto-maternal interface of human pregnancy

OBJECTIVE AND DESIGN

To localise mRNAs for the histamine receptors H1, H2 and H3, and for diamine oxidase, in the placenta and decidua of the human feto-maternal interface.

MATERIALS AND METHODS

Complementary DNA for each mRNA of interest was amplified by polymerase chain reaction. Sub-cloned sequences were used to prepare probes for in situ hybridisation, and these were employed to localise the expression of mRNAs for histamine receptors H1 and H2, and for diamine oxidase.

RESULTS

mRNA for histamine receptors H1 and H2, and for diamine oxidase could be detected at the feto-maternal interface of human pregnancy, and localised to both decidual and placental cells.

CONCLUSION

The co-expression of these receptors and DAO is consistent with a role for histamine at the feto-maternal interface of human pregnancy.

Histamine upregulates Th1 and downregulates Th2 responses due to different patterns of surface histamine 1 and 2 receptor expression

Histamine, which acts via G protein-coupled receptors, is an important mediator of immediate hypersensitivity and is also able to influence the nature of T cell responses. We demonstrated that TH1 and Th2 cells express distinct surface histamine receptor patterns and that Th1-type responses are enhanced by histamine, whereas Th2-type responses are negatively regulated, due to different intracellular signals generated by histamine stimulation. These findings account for negative feedback regulation in a wide variety of pathologies.

Quantification of human H1 histamine receptor mRNA from peripheral blood

STUDY OBJECTIVE

To develop a reverse transcription (RT)-polymerase chain reaction (PCR) technique to detect and quantify human histamine1 (H1) receptor mRNA in peripheral blood.

METHODS

Primer pairs were based on the human H1 receptor nucleotide sequence. A competitive reference standard (CRS) was developed that used the same primers as wild-type mRNA but contained a 92-bp deletion. RT-PCR was performed with 5 microg of total RNA obtained from venous blood of six subjects that was added to known concentrations of CRS RNA. Linear regression comparing wild-type with CRS product was used to quantify wild-type mRNA.

MEASUREMENTS AND MAIN RESULTS

Three subjects had detectable H1 mRNA, with a range of 31-435 pg. In three subjects PCR product was not detected, although the presence of RNA was confirmed. Redesigned primer pairs showed mRNA to H1 receptor in two of the remaining subjects, but it was undetectable in the third.

CONCLUSION

RT-PCR can be used to detect and quantify human H1 receptor mRNA from peripheral blood.

Cysteinyl leukotrienes mediate histamine hypersensitivity ex vivo by increasing histamine receptor numbers

BACKGROUND

Hyperresponsiveness to histamine is a key feature of a variety of pathological conditions, including bronchial asthma, food allergy, colitis ulcerosa, and topical allergic disorders. Cells isolated from hyperresponsive individuals do not display exaggerated histamine responses ex vivo and thus the molecular mechanisms underlying histamine responsiveness remain obscure. Importantly, several in vivo observations implicate cysteinyl leukotrienes as possible mediators of increased histamine responses. We decided to investigate whether cysteinyl leukotrienes enhance the cellular reaction to histamine in cell types involved in pathological and immunological histamine hyperresponsiveness, as this might provide an in vitro system for studying histamine responsiveness and could shed light on the underlying molecular mechanisms.

MATERIALS AND METHODS

Histamine responsiveness was determined by measuring histamine-induced prostaglandin E(2) production. Scatchard analysis was performed to determine the number of histamine H(1) receptors. Mouse macrophages, primary isolated human peripheral blood monocytes, and human umbilical smooth muscle cells were investigated before and after cysteinyl leukotriene stimulation.

RESULTS

In all three cell types tested, cysteinyl leukotrienes instantaneously enhanced histamine-induced prostaglandin E(2) production. This increase in prostaglandin E(2) production coincided with the immediate and transient appearance of additional H(1) receptors on the plasma membrane.

CONCLUSIONS

Cysteinyl leukotrienes prime histamine responses by recruiting additional histamine receptors in immunologically relevant cell types in vitro.

Analysis of dissociated single neurons by simple and semi-quantitative RT-PCR (reverse transcription and polymerase chain reaction)

We have developed a simple and semi-quantitative method for mRNA determination in single cells using the reverse transcription and polymerase chain reaction (RT-PCR). The distinct features of this method are the highly efficient RNA harvest from whole dissociated cells and the ability to perform all RT procedures in one tube that allowed semi-quantitative determination of mRNA in dissociated cells. This method revealed that histamine H1-receptor mRNA was highly expressed in 5/28 small and 1/26 large dorsal root ganglion neurons of the mouse.

Interleukin-4 stimulates rheumatoid synovial fibroblasts to express matrix metalloproteinase-1 (tissue collagenase) and histamine H1 receptor mRNA

In the present study, we investigated the effect of interleukin-4 (IL-4) on metalloproteinase 1 (MMP-1/tissue collagenase) production in human rheumatoid synovial fibroblasts. Northern blot analysis revealed that addition of IL-4 with or without histamine stimulated the cells to increase the amount of proMMP-1 mRNA, and the IL-4 with histamine addition resulted in a 3.3-fold increase compared with histamine only. Furthermore, IL-4 itself stimulated the expression of histamine H1 receptor mRNA. These results suggest that IL-4 may play an important role in joint destruction in RA.

Regulation of the human histamine H1 receptor stably expressed in Chinese hamster ovary cells

1. The human H1 receptor gene expressed in Chinese hamster ovary cells (CHOhumH1) encodes a classical histamine H1 receptor with a pharmacology similar to that of the H1 receptor found in guinea-pig cerebellum and the endogenously expressed human H1 receptor in 1321N1 astrocytoma cells as determined by [3H]-mepyramine binding studies. 2. In CHOhumH1 cells, histamine induced a concentration-dependent rise in inositol phosphates (EC50 2.23 +/- 0.97 microM) and a rapid increase of [Ca2+]i, followed by a sustained increase of [Ca2+]i upon addition of 100 microM histamine. 3. Short-term exposure of CHOhumH1 cells to histamine (100 microM) resulted in a decrease of subsequent histamine-induced Ca2+ responses. The histamine-induced desensitization appeared to be heterologous as the ATP-induced Ca2+ response was also found to be affected. 4. The process of heterologous histamine-induced desensitization of the Ca2+ response in CHOhumH1 cells can be ascribed to an alteration at the level of the intracellular Ca2+ pool, as the Ca2+ response of caffeine (10 mM), which releases Ca2+ from intracellular Ca2+ stores was also attenuated upon short-term histamine exposure. 5. In CHOhumH1 cells the PKC activator, PMA, was found to inhibit the histamine (100 microM)-induced Ca2+ response concentration-dependently (IC50 0.2 +/- 0.03 microM) as well as the ATP (100 microM)-induced Ca2+ response. However, this inhibition was only partial and less effective than histamine-pretreatment. Moreover, in CHOhumH1 cells PKC downregulation induced by long-term exposure to PMA (1 microM) did not affect the histamine-induced desensitization nor did pretreatment with the specific PKC inhibitor Ro-31-8220 (10 microM), indicating that in CHOhumH1 cells PKC is probably not involved in the heterologous desensitization. 6. Long-term treatment of CHOhumH1 cells with histamine or other H1 agonists resulted in a time- and concentration-dependent decrease in the number of H1 receptor binding sites (maximal reduction: 47 +/- 5%). 7. Long-term exposure of CHOhumH1 cells to ATP or PMA did not affect H1 receptor density. 8. Both histamine (100 microM)- and ATP (100 microM)-induced Ca2+ responses were affected upon long-term exposure of cells to histamine (100 microM), which might be explained by an alteration at a level distant from the receptor. 9. These results show that in CHOhumH1 cells the human histamine H1 receptor is susceptible to short-term and long-term receptor regulation in which PKC does not seem to play a role. The CHOhumH1 cells therefore provide an excellent model system for studying the mechanism(s) of PKC-independent H1 receptor regulation.

Expression of the histamine H1 receptor gene in relation to atherosclerosis

Histamine in serum and arterial tissue contributes to the pathogenesis of atherosclerosis and the formation of coronary artery vasospasm. As the effect of histamine at a given site will be mediated by its specific receptors, we investigated by in situ hybridization and Northern blot analysis the expression and localization of human histamine H1 receptor mRNA in the arterial wall and in cultured human aortic intimal smooth muscle cells (SMC) and immortalized SMC (ISS10) and endothelial cells (SE1). In situ hybridization showed that SMC and endothelial cells expressed H1 receptor mRNA in vivo and that the expression was increased in SMC in the thickened intima of atherosclerotic foci in both the aorta and coronary artery. By Northern blot analysis, we also detected histamine H1 receptor mRNA in cultured SMC, ISS10, and SE1 and found that platelet-derived growth factor stimulated SMC to increase their expression of the mRNA in vitro. These results suggest that up-regulation of histamine H1 receptor expression by platelet-derived growth factor plays an important role in the initiation and progression of cardiovascular diseases.

Endogenous expression of histamine H1 receptors functionally coupled to phosphoinositide hydrolysis in C6 glioma cells: regulation by cyclic AMP

1. The effects of histamine receptor agonists and antagonists on phospholipid hydrolysis in rat-derived C6 glioma cells have been investigated. 2. Histamine H1 receptor-stimulation caused a concentration-dependent increase in the accumulation of total [3H]-inositol phosphates in cells prelabelled with [3H]-myo-inositol. The rank order of agonist potencies was histamine (EC50 = 24 microM) > N alpha-methylhistamine (EC50 = 31 microM) > 2-thiazolylethylamine (EC50 = 91 microM). 3. The response to 0.1 mM histamine was antagonized in a concentration-dependent manner by the H1-antagonists, mepyramine (apparent Kd = 1 nM) and (+)-chlorpheniramine (apparent Kd = 4 nM). In addition, (-)-chlorpheniramine was more than two orders of magnitude less potent than its (+)-stereoisomer. 4. Elevation of intracellular cyclic AMP accumulation with forskolin (10 microM, EC50 = 0.3 microM), isoprenaline (1 microM, EC50 = 4 nM) or rolipram (0.5 mM), significantly reduced the histamine-mediated (0.1 mM) inositol phosphate response by 37%, 43% and 26% respectively. In contrast, 1,9-dideoxyforskolin did not increase cyclic AMP accumulation and had no effect on the phosphoinositide response to histamine. 5. These data indicate the presence of functionally coupled, endogenous histamine H1 receptors in C6 glioma cells. Furthermore, the results also indicate that H1 receptor-mediated phospholipid hydrolysis is inhibited by the elevation of cyclic AMP levels in these cells.

Stable expression of human H1-histamine-receptor cDNA in Chinese hamster ovary cells. Pharmacological characterisation of the protein, tissue distribution of messenger RNA and chromosomal localisation of the gene

A cDNA clone for the histamine H1 receptor was isolated from a human lung cDNA library; it encoded a protein of 487 amino acids which showed characteristic features of G-protein-coupled receptors. The percentages of identity of the deduced amino acid sequence with bovine, rat and guinea pig H1 histamine receptors were 82.6%, 79.4% and 73.3%, respectively, whereas these percentages decreased to 74.6%, 66% and 56.7% for the amino acid sequence of the third intracellular loop. The human H1-receptor cDNA was transfected into Chinese hamster ovary cells (CHO) via an eukaryotic expression vector; the receptor protein present on cell membranes specifically bound [3H]mepyramine with a Kd of 3.7 nM. The binding was displaced by H1-histamine-receptor antagonists and histamine. Northern blot analysis indicated the presence of two histamine H1 receptor mRNAs of 3.5 kb and 4.1 kb in various human tissues and an additional mRNA of 4.8 kb restricted to the human brain. Finally, by means of somatic cell hybrids segregating either human or rat chromosomes, the gene for histamine H1 receptor was found to reside on human chromosome 3 and rat chromosome 4.

An immortalised murine hypothalamic neuronal cell, GT1-7, expresses functional histamine H1 receptors

Histamine, acting via H1 receptors, dose-dependently stimulated [3H]inositol phosphate production in GT1-7 neuronal cells. GT1-7 cells also responded to Substance P but not to other neuroactive drugs tested. Acute histamine pretreatment desensitised the histamine-induced response, resulting in a reduction in the maximal response and a slower time-course of [3H]-inositol phosphate production. The desensitisation phenomenon was reversible, with full recovery by 2 h.

Molecular cloning of the human histamine H1 receptor gene

The human histamine H1 receptor gene, an intron-lacking gene, was isolated with bovine H1 receptor cDNA [Yamashita, M., Fukui, H., Sugama, K., Horio, Y., Ito, S., Mizuguchi, H., and Wada, H. (1991) Proc. Natl. Acad. Sci. USA 88, 11515-11519] used as a probe. The receptor protein deduced from the nucleotide sequence of this gene was composed of 487 amino acid residues with a calculated Mr of 55,781 and possessed characteristic properties of GTP binding protein-coupled receptors. At the 5' flanking region of the human H1 receptor gene, we located potential TATA box and CACCC sequences, AP1 binding site-like sequences, glucocorticoid responsive element-like sequences, and other binding sequences for inducers. Northern blot analysis showed that H1 receptor mRNAs visualized as two bands with 3.0-kilobase and 3.5-kilobase nucleotides were expressed in peripheral tissues such as placenta, lung, skeletal muscle, and kidney and that only one species with 3.5-kilobase nucleotides was present in the brain. H1 receptor mRNA was most abundant in the placenta. The human H1 receptor gene was mapped to the chromosome 3p25 by the fluorescence in situ hybridization method.

Expression and characterization of the bovine histamine H1 receptor in cDNA-transfected C6 astroglioma cells

Rat C6 astroglioma cells (C6-bH1R cells) expressing cloned bovine histamine H1 receptors were established by transfection with a vector (pEF-BOS-bH1R) which carried a 2.7-kbp EcoRI fragment of the bovine H1 receptor cDNA [Yamashita, M. et al. (1991) Proc. Natl. Acad. Sci. USA 88, 11515-11519]. The cloned bovine H1 receptor in C6-bH1R cells was characterized by three established criteria: the [3H]mepyramine binding assay, the accumulation of inositol phosphates induced by histamine, and histamine-induced elevation of intracellular Ca2+ concentration ([Ca2+]i). The accumulation of inositol phosphates induced by histamine was time- and dose-dependent. The accumulation of inositol trisphosphate was biphasic with a prompt increase to the maximal level, followed by a sustained submaximal level. The histamine-induced accumulation of inositol phosphates was suppressed by phorbol ester, but not by pertussis toxin. Results from the [3H]-mepyramine binding assay and histamine-induced elevation of [Ca2+]i were characteristic of H1 receptors. Several compounds among tricyclic antidepressants, neuroleptics, and serotonin antagonists showed affinities to the cloned bovine H1 receptor with Ki values similar to reported values. Histamine neither induced cAMP accumulation nor attenuated forskolin-induced cAMP accumulation in C6-bH1R cells. C6-bH1R cells are particularly useful for studying the H1 receptor-mediated astroglial cell functions.

Histamine-induced microvascular leakage in pial venules: differences between the SJL/J and BALB/c inbred strains of mice

The actions of histamine on pial venule leaky site formation were measured intravitally in two inbred strains of mice (BALB/c and SJL/J). Pial venules were visualized using a cranial window microscopy technique, and microvascular leaky site formation was assessed visually using a fluorescein-dextran indicator. SJL/J mice were found to be sensitive to histamine-induced leakage, whereas the BALB/c strain was refractory. Exposure to pertussis toxin enhanced the sensitivity to histamine in the SJL/J strain, but little effect was observed for BALB/c mice. However, the employment of a polymerase chain reaction (PCR) technique for the detection of mRNA for histamine H1 receptor identified receptor-specific message in isolated cerebrovascular endothelium from both strains of mice. The lack of pial responsiveness in the BALB/c mice remains unexplained. Mast cells in the dura mater were found to be more numerous in SJL/J mice than in BALB/c mice. This observation supports previous observations of strain-specific differences in CNS inflammation. The results support the concept that genetically controlled differences in vascular sensitivity and localization of CNS-associated mast cells may play important roles in the generation of vasogenic edema and inflammation in CNS trauma and disease.

Genomic cloning, heterologous expression and pharmacological characterization of a human histamine H1 receptor

A human histamine H1 receptor gene lacking introns was isolated by screening a human genomic library with a bovine histamine H1 receptor probe. The deduced protein of 487 amino acids showed characteristic properties of G-protein-coupled receptors. The coding region was subcloned into the expression vector pSVL (Pharmacia), and the resulting construct transfected into COS-7 cells. Binding studies with [3H]pyrilamine on membranes from transfected cells revealed saturable specific binding with a KD of 1.2 nM and a Bmax of 3400 fmol/mg protein. Binding affinities of histamine and known histamine antagonists were similar to those for histamine H1 receptors in guinea-pig cerebellum. In transfected COS-7 cells, histamine induced inositol phosphate formation, that was inhibitable by pyrilamine.

High, stable expression of the bovine histamine H1-receptor coupled to [Ca2+]i mobilisation in CHO-K1 cells

The bovine H1-receptor DNA was transfected into Chinese hamster ovary cells (CHO-K1) using an expression vector. Binding studies revealed very high expression levels of the receptor which was found to have a Kd for [3H]-mepyramine of 1 nM. Addition of histamine resulted in a concentration-dependent increase in intracellular calcium which was found to involve both release from intracellular stores and entry across the plasma membrane. Furthermore, the response demonstrated the pharmacological characteristics of an H1-receptor-mediated event. Thus, we present the first report of the high, functional expression of the bovine H1-receptor coupled to mobilisation of intracellular calcium in CHO-K1 cells.

Expression of histamine H1 receptors in autoimmune myocarditis mice

Two populations of histaminergic H1 receptors with distinct high and low affinity binding sites were characterized by the specific H1 receptor antagonist [3H]mepyramine in autoimmune myocardium. No saturable binding of the radiolabelled H1 antagonist was observed in normal myocardium. Reaction of autoimmune myocardium with specific H1 agonist (2-thiazolylethylamine (ThEA)) triggered positive inotropy and negative chronotropy, which were inhibited by mepyramine. Inhibitors of phospholipase C and protein kinase C attenuated both the inotropic and chronotropic effects of ThEA, suggesting the participation of phosphoinositide hydrolysis in this phenomenon. The latter was verified by measurement of polyphosphoinositide hydrolysis in autoimmune myocardium following the reaction of ThEA with histaminergic H1 receptors. We conclude that functional H1 histaminergic receptors could involve a distinctive mechanism operating in autoimmune myocardium as a result of cardiac antigen immunization.

Control of histamine induced inositol phospholipid hydrolysis in cultured human tracheal smooth muscle cells

[3H]Inositol phosphate responses to histamine and a range of other agonists were studied in cultured human tracheal smooth muscle cells. Histamine (EC50 6.5 microM), bradykinin (EC50 9.7 nM), carbachol (EC50 10 microM), substance P and NaF all produced concentration dependent [3H]inositol phosphate formation in these cells. The response to histamine was inhibited by mepyramine (KA 4.3 x 10(9) M-1), indicating the involvement of the histamine H1 receptor in this response. The inositol phosphate response to histamine was apparently desensitized following prolonged agonist exposure. The response to histamine was inhibited by phorbol dibutyrate (IC50 6 nM), and this inhibitory effect was reversed by staurosporine (150 nM). Isoprenaline (1 microM), rolipram (0.1-100 microM) and 3-isobutyl-1-methylxanthine (0.1 mM) all produced small inhibitory effects upon histamine induced inositol phosphate formation. These results demonstrate that cultured human tracheal smooth muscle cells express histamine H1 receptors coupled to phosphoinositidase C and suggest that the inositol phosphate response induced by stimulation of this receptor subtype is inhibited by activation of protein kinase C and, to a lesser extent, by elevation of cell cyclic AMP content.

Alcohol-induced bronchospasm in an asthmatic patient: pharmacologic evaluation of the mechanism

A 23-year-old Asian with histamine-reactive asthma complained of recurrent chest tightness, nasal congestion and flushing immediately after drinking minimal amounts of alcoholic beverages. He was extensively studied to determine the possible mechanism of his alcohol-induced respiratory symptoms. Drinking of either beer or 95 percent ethanol in apple juice immediately provoked vasomotor signs and moderately severe bronchospasm (54 percent and 73 percent decreases in specific airway conductance, respectively), which spontaneously improved over 30 minutes and two hours, respectively. Intravenous and inhaled ethanol caused less bronchospasm than observed with oral ethanol, and recovery was rapid. Pretreatment with cromolyn sodium (inhaled or oral) and isoproterenol had no inhibitory effect on the alcohol-induced bronchoconstriction, whereas atropine, acetylsalicylic acid, cyproheptadine, and chlorpheniramine appeared to have a partial inhibitory effect. Approximately 70 percent inhibition was observed after chlorpheniramine. Observations in this patient suggest that the bronchoconstriction induced by alcoholic beverages is related to their ethanol content and may be related to formation or release of one or more bronchoconstrictor and vasoactive compounds, including a stimulant of histamine1-receptors. The route of ethanol administration may also influence the bronchospastic response.