Histamine-induced calcium release and phorbol antagonism in cultured airway smooth muscle cells

Epithelial Cells Induce a Cyclo-Oxygenase-1-Dependent Endogenous Reduction in Airway Smooth Muscle Contractile Phenotype

Airway smooth muscle cells (ASMCs) are phenotypically regulated to exist in either a proliferative or a contractile state. However, the influence of other airway structural cell types on ASMC phenotype is largely unknown. Although epithelial cells are known to drive ASM proliferation, their effects on the contractile phenotype are uncertain. In the current study, we tested the hypothesis that epithelial cells reduce the contractile phenotype of ASMCs. To do so, we measured force production by traction microscopy, gene and protein expression, as well as calcium release by Fura-2 ratiometric imaging. ASMCs incubated with epithelial-derived medium produced less force after histamine stimulation. We observed reduced expression of myocardin, α-smooth muscle actin, and calponin within ASMCs after coculture with epithelial cells. Peak calcium release in response to histamine was diminished, and depended on the synthesis of cyclo-oxygenase-1 products by ASM and on prostaglandin E receptors 2 and 4. Together, these in vitro results demonstrate that epithelial cells have the capacity to coordinately reduce ASM contraction by functional antagonism and by reduction of the expression of certain contractile proteins.

Olfactory Receptors Modulate Physiological Processes in Human Airway Smooth Muscle Cells

Pathophysiological mechanisms in human airway smooth muscle cells (HASMCs) significantly contribute to the progression of chronic inflammatory airway diseases with limited therapeutic options, such as severe asthma and COPD. These abnormalities include the contractility and hyperproduction of inflammatory proteins. To develop therapeutic strategies, key pathological mechanisms, and putative clinical targets need to be identified. In the present study, we demonstrated that the human olfactory receptors (ORs) OR1D2 and OR2AG1 are expressed at the RNA and protein levels in HASMCs. Using fluorometric calcium imaging, specific agonists for OR2AG1 and OR1D2 were identified to trigger transient Ca²⁺ increases in HASMCs via a cAMP-dependent signal transduction cascade. Furthermore, the activation of OR2AG1 via amyl butyrate inhibited the histamine-induced contraction of HASMCs, whereas the stimulation of OR1D2 with bourgeonal led to an increase in cell contractility. In addition, OR1D2 activation induced the secretion of IL-8 and GM-CSF. Both effects were inhibited by the specific OR1D2 antagonist undecanal. We herein provide the first evidence to show that ORs are functionally expressed in HASMCs and regulate pathophysiological processes. Therefore, ORs might be new therapeutic targets for these diseases, and blocking ORs could be an auspicious strategy for the treatment of early-stage chronic inflammatory lung diseases.

Diminution of signal transducer and activator of transcription 3 signaling inhibits vascular permeability and anaphylaxis

BACKGROUND

During IgE-mediated immediate hypersensitivity reactions, vascular endothelial cells permeabilize in response to mast cell mediators. We have demonstrated previously that patients and mice with signal transducer and activator of transcription 3 (STAT3) mutations (autosomal dominant hyper-IgE syndrome [AD-HIES]) are partially protected from anaphylaxis.

OBJECTIVES

We sought to study the mechanism by which STAT3 contributes to anaphylaxis and determine whether small-molecule inhibition of STAT3 can prevent anaphylaxis.

METHODS

Using unaffected and STAT3-inhibited or genetic loss-of-function samples, we performed histamine skin prick tests, investigated the contribution of STAT3 to animal models of anaphylaxis, and measured endothelial cell permeability, gene and protein expression, and histamine receptor-mediated signaling.

RESULTS

Although mouse mast cell degranulation was minimally affected by STAT3 blockade, mast cell mediator-induced anaphylaxis was blunted in Stat3 mutant mice with AD-HIES and in wild-type mice subjected to small-molecule STAT3 inhibition. Histamine skin prick test responses were diminished in patients with AD-HIES. Human umbilical vein endothelial cells derived from patients with AD-HIES or treated with a STAT3 inhibitor did not signal properly through Src or cause appropriate dissolution of the adherens junctions made up of the proteins vascular endothelial-cadherin and β-catenin. Furthermore, we found that diminished STAT3 target microRNA17-92 expression in human umbilical vein endothelial cells from patients with AD-HIES is associated with increased phosphatase and tensin homolog (PTEN) expression, which inhibits Src, and increased E2F transcription factor 1 expression, which regulates β-catenin cellular dynamics.

CONCLUSIONS

These data demonstrate that STAT3-dependent transcriptional activity regulates critical components for the architecture and functional dynamics of endothelial junctions, thus permitting vascular permeability.

Serotonin and Histamine Therapy Increases Tetanic Forces of Myoblasts, Reduces Muscle Injury, and Improves Grip Strength Performance of Dmd(mdx) Mice

Duchenne muscular dystrophy (DMD) is a recessive X-linked fatal disorder caused by a mutation in the dystrophin gene. Although several therapeutic approaches have been studied, none has led to substantial long-term effects in patients. The aim of this study was to test a serotonin and histamine (S&H) combination on human skeletal myoblasts and Dmd(mdx) mice for its effects on muscle strength and injury. Normal human bioartificial muscles (BAMs) were treated, and muscle tetanic forces and muscle injury tests were performed using the MyoForce Analysis System. Dmd(mdx) mice, the murine model of DMD, were administered serotonin, histamine, or S&H combination twice daily for 6 weeks, and functional performance tests were conducted once a week. The S&H combination treatment caused significant increases in tetanic forces at all time points and concentrations tested as compared to the saline controls. Dose response of the BAMs to the treatment demonstrated a significant increase in force generation at all concentrations compared to the controls after 3 to 4 days of drug treatment. The highest 3 concentrations had a significant effect on lowering contractile-induced injury as measured by a reduction in the release of adenylate kinase. Histamine-only and S&H treatments improved grip strength of Dmd(mdx) mice, whereas serotonin-only treatment resulted in no significant improvement in muscle strength. The results of this study indicate that S&H therapy might be a promising new strategy for muscular dystrophies and that the mechanism should be further investigated.

TRPC6 is the endothelial calcium channel that regulates leukocyte transendothelial migration during the inflammatory response

Weber et al. identify TRPC6 as the calcium channel mediating the transient increase in endothelial cytosolic free calcium concentration required for transendothelial migration of leukocytes during the inflammatory response.

Leukocyte transendothelial migration (TEM) is a tightly regulated, multistep process that is critical to the inflammatory response. A transient increase in endothelial cytosolic free calcium ion concentration (↑[Ca²⁺]_i) is required for TEM. However, the mechanism by which endothelial ↑[Ca²⁺]_i regulates TEM and the channels mediating this ↑[Ca²⁺]_i are unknown. Buffering ↑[Ca²⁺]_i in endothelial cells does not affect leukocyte adhesion or locomotion but selectively blocks TEM, suggesting a role for ↑[Ca²⁺]_i specifically for this step. Transient receptor potential canonical 6 (TRPC6), a Ca²⁺ channel expressed in endothelial cells, colocalizes with platelet/endothelial cell adhesion molecule-1 (PECAM) to surround leukocytes during TEM and clusters when endothelial PECAM is engaged. Expression of dominant-negative TRPC6 or shRNA knockdown in endothelial cells arrests neutrophils apically over the junction, similar to when PECAM is blocked. Selectively activating endothelial TRPC6 rescues TEM during an ongoing PECAM blockade, indicating that TRPC6 functions downstream of PECAM. Furthermore, endothelial TRPC6 is required for trafficking of lateral border recycling compartment membrane, which facilitates TEM. Finally, mice lacking TRPC6 in the nonmyeloid compartment (i.e., endothelium) exhibit a profound defect in neutrophil TEM with no effect on leukocyte trafficking. Our findings identify endothelial TRPC6 as the calcium channel mediating the ↑[Ca²⁺]_i required for TEM at a step downstream of PECAM homophilic interactions.

Gene expression in asthmatic airway smooth muscle: a mixed bag

It has long been known that airway smooth muscle (ASM) contraction contributes significantly to the reversible airflow obstruction that defines asthma. It has also been postulated that phenotypic changes in ASM contribute to the airway hyper-responsiveness (AHR) that is a characteristic feature of asthma. Although there is agreement that the mass of ASM surrounding the airways is significantly increased in asthmatic compared with non-asthmatic airways, it is still uncertain whether there are quantitative or qualitative changes in the level of expression of the genes and proteins involved in the canonical contractile pathway in ASM that could account for AHR. This review will summarize past attempts at quantifying gene expression changes in the ASM of asthmatic lungs as well as non-asthmatic ASM cells stimulated with various inflammatory cytokines. The lack of consistent findings in asthmatic samples coupled with the relative concordance of results from stimulated ASM cells suggests that changes to the contractility of ASM tissues in asthma may be dependent on the presence of an inflammatory environment surrounding the ASM layer. Removal of the ASM from this environment could explain why hypercontractility is rarely seen ex vivo.

Models to study airway smooth muscle contraction in vivo, ex vivo and in vitro: implications in understanding asthma

Asthma is a chronic obstructive airway disease characterised by airway hyperresponsiveness (AHR) and airway wall remodelling. The effector of airway narrowing is the contraction of airway smooth muscle (ASM), yet the question of whether an inherent or acquired dysfunction in ASM contractile function plays a significant role in the disease pathophysiology remains contentious. The difficulty in determining the role of ASM lies in limitations with the models used to assess contraction. In vivo models provide a fully integrated physiological response but ASM contraction cannot be directly measured. Ex vivo and in vitro models can provide more direct assessment of ASM contraction but the loss of factors that may modulate ASM responsiveness and AHR, including interaction between multiple cell types and disruption of the mechanical environment, precludes a complete understanding of the disease process. In this review we detail key advantages of common in vivo, ex vivo and in vitro models of ASM contraction, as well as emerging tissue engineered models of ASM and whole airways. We also highlight important findings from each model with respect to the pathophysiology of asthma.

Histamine differentially regulates the production of Th1 and Th2 chemokines by keratinocytes through histamine H1 receptor

Histamine is a biological amine that plays an important role in allergic responses. However, the involvement of histamine signaling in late allergic responses in the skin is poorly understood. Therefore, we attempted to investigate the involvement of histamine signaling in late allergic responses, especially in keratinocytes (KCs). HaCaT KCs and normal human KCs (NHKs) predominantly expressed histamine H1 receptor (H1R) and H2 receptor (H2R). Histamine suppressed tumor necrosis factor α (TNF-α)- and interferon-γ (IFN-γ)-induced production of CC chemokine ligand 17(CCL17), a type 2 T-helper (Th2) chemokine, by HaCaT KCs. It suppressed the phosphorylation of p38 mitogen-activated protein (MAP) kinase, but not that of extracellular signal-regulated kinases (ERKs), and TNF-α- and IFN-γ-induced nuclear factor κB (NFκB) activity. In contrast, histamine enhanced the production of CXC chemokine ligand 10 (CXCL10), a Th1 chemokine, by TNF-α- and IFN-γ-stimulated HaCaT KCs and NHKs. TNF-α- and IFN-γ-induced CXCL10 production was upregulated by suppression of p38 MAP kinase or NF-κB activity, which could explain histamine involvement. We concluded that histamine suppresses CCL17 production by KCs by suppressing p38 MAP kinase and NF-κB activity through H1R and may act as a negative-feedback signal for existing Th2-dominant inflammation by suppressing CCL17 and enhancing CXCL10 production.

Histamine: metabolism, physiology, and pathophysiology with applications in veterinary medicine

OBJECTIVE

To review the human and veterinary literature on histamine physiology and pathophysiology and potential applications for clinical use in veterinary critical care.

DATA SOURCES

Human and veterinary clinical studies, reviews, texts, and recent research in histamine receptor and antagonist therapy.

HUMAN DATA SYNTHESIS

Recent progress in molecular biology has led to a more complete understanding of the enzymes involved in histamine metabolism and histamine receptor physiology. The past decade of research has confirmed the role of histamine in the classical functions (contraction of smooth muscle, increase in vascular permeability, and stimulation of gastric acid secretion) and has also elucidated newer ones that are now under investigation. Data on the roles of histamine in angiogenesis, circadian rhythm, bone marrow regeneration, bacterial eradication, and cancer are emerging in the literature. Newer histamine antagonists are currently in drug trials and are expected to advance the clinical field in treatment of allergic, gastrointestinal, and cognitive disorders.

VETERINARY DATA SYNTHESIS

Veterinary histamine research is directed at identifying the effects of certain pharmacological agents on blood histamine concentrations and establishing the relevance in clinical disease states. Research demonstrates important species differences in regards to histamine receptor physiology and tissue response. Studies in the area of trauma, sepsis, anaphylaxis, allergy, and gastrointestinal disorders have direct applications to clinical veterinary medicine.

CONCLUSIONS

Histamine plays a key role in the morbidity and mortality associated with allergy, asthma, gastric ulcers, anaphylaxis, sepsis, hemorrhagic shock, anesthesia, surgery, cardiovascular disease, cancer, CNS disorders, and immune-mediated disease. Histamine antagonism has been in common use to block its adverse effects. With recent advances in the understanding of histamine receptor physiology, pharmaceutical agents targeting these receptors have increased the therapeutic options.

Abnormal spatial diffusion of Ca2+ in F508del-CFTR airway epithelial cells

Background

In airway epithelial cells, calcium mobilization can be elicited by selective autocrine and/or paracrine activation of apical or basolateral membrane heterotrimeric G protein-coupled receptors linked to phospholipase C (PLC) stimulation, which generates inositol 1,4,5-trisphosphate (IP₃) and 1,2-diacylglycerol (DAG) and induces Ca²⁺ release from endoplasmic reticulum (ER) stores.

Methods

In the present study, we monitored the cytosolic Ca²⁺ transients using the UV light photolysis technique to uncage caged Ca²⁺ or caged IP₃ into the cytosol of loaded airway epithelial cells of cystic fibrosis (CF) and non-CF origin. We compared in these cells the types of Ca²⁺ receptors present in the ER, and measured their Ca²⁺ dependent activity before and after correction of F508del-CFTR abnormal trafficking either by low temperature or by the pharmacological corrector miglustat (N-butyldeoxynojirimycin).

Results

We showed reduction of the inositol 1,4,5-trisphosphate receptors (IP₃R) dependent-Ca²⁺ response following both correcting treatments compared to uncorrected cells in such a way that Ca²⁺ responses (CF+treatment vs wild-type cells) were normalized. This normalization of the Ca²⁺ rate does not affect the activity of Ca²⁺-dependent chloride channel in miglustat-treated CF cells. Using two inhibitors of IP₃R1, we observed a decrease of the implication of IP₃R1 in the Ca²⁺ response in CF corrected cells. We observed a similar Ca²⁺ mobilization between CF-KM4 cells and CFTR-cDNA transfected CF cells (CF-KM4-reverted). When we restored the F508del-CFTR trafficking in CFTR-reverted cells, the specific IP₃R activity was also reduced to a similar level as in non CF cells. At the structural level, the ER morphology of CF cells was highly condensed around the nucleus while in non CF cells or corrected CF cells the ER was extended at the totality of cell.

Conclusion

These results suggest reversal of the IP₃R dysfunction in F508del-CFTR epithelial cells by correction of the abnormal trafficking of F508del-CFTR in cystic fibrosis cells. Moreover, using CFTR cDNA-transfected CF cells, we demonstrated that abnormal increase of IP₃R Ca²⁺ release in CF human epithelial cells could be the consequence of F508del-CFTR retention in ER compartment.

The noncompetitive antagonism of histamine H1 receptors expressed in Chinese hamster ovary cells by olopatadine hydrochloride: its potency and molecular mechanism

Calcium responses to various concentrations of histamine were monitored in Chinese hamster ovary cells stably expressing the human histamine H(1) receptor. The effects of various histamine H(1) receptor antagonists on the dose-response curve for histamine were evaluated. Olopatadine hydrochloride (olopatadine) inhibited the histamine-induced maximum response (pD(2)': 7.5) but had insignificant effects on histamine EC(50) values. This noncompetitive property exhibited by olopatadine, which was also observed in human umbilical vein endothelial cells, was the most striking among the antihistamines tested in this study. The geometrical isomer of olopatadine (E-isomer), which had a similar binding affinity to the histamine H(1) receptor as olopatadine, showed a mixed antagonistic profile (competitive and noncompetitive). These results indicate that the geometry around the double bond in the dimethylaminopropylidene group is critical for the potent noncompetitive property of olopatadine. Furthermore, binding mode analyses suggest that the protonated amine group in the dimethylaminopropylidene moiety of olopatadine forms an ionic bond with Glu 181 that is present in the second extracellular loop of the histamine H(1) receptor, whereas the amine group of the E-isomer does not. The second extracellular loop in aminergic G-protein-coupled receptors contributes to ligand binding and therefore the noncompetitive property of olopatadine may be explained by the interaction with Glu 181.

Calcium homeostasis is abnormal in cystic fibrosis airway epithelial cells but is normalized after rescue of F508del-CFTR

Retention of F508del-CFTR proteins in the endoplasmic reticulum (ER) is dependent upon chaperone proteins, many of which require Ca(2+) for optimal activity. Here, we show in human tracheal gland CF-KM4 cells, that after correction of F508del-CFTR trafficking by miglustat (N-butyldeoxynojirimycin) or low temperature (27 degrees C), the Ca(2+) mobilization is decreased compared to uncorrected cells and becomes identical to the Ca(2+) response observed in non-CF MM39 cells. In CF-KM4 and human nasal epithelial CF15 cells, we also show that inhibiting vesicular trafficking by nocodazole prevents not only the rescue of F508del-CFTR but also the Ca(2+) mobilization decrease. Finally, experiments using the CFTR inhibitor CFTR(inh)-172 showed that the presence but not the channel activity of F508del-CFTR at the plasma membrane is required to decrease the Ca(2+) mobilization in corrected CF cells. These findings show that correction of the abnormal trafficking of F508del-CFTR proteins might have profound consequences on cellular homeostasis such as the control of intracellular Ca(2+) level.

H1-receptors: localization and role in airway physiology and in immune functions

Histamine H(1)-receptors are involved in the pathologic processes of allergy. Clinical trials of H(1)-receptor antagonists have demonstrated the efficacy of these agents in reducing the sneezing, pruritus, and rhinorrhea associated with allergic rhinitis. In the lung, H(1)-receptors mediate the bronchoconstrictive effects of histamine and increase vascular permeability, which lead to plasma exudation. H(1)-receptors are present on T cells, B cells, monocytes, and lymphocytes, and stimulation of these receptors induces pro-inflammatory effects. It has been suggested that a signal from the H(1)-receptor contributes to the antigen receptor-mediated signaling pathways that induce proliferative responses and lead to the production of cytokines and antibodies by T cells and B cells, respectively. It would appear, therefore, that the H(1)-receptor has a wider role in inflammatory processes than simply mediating the actions of histamine.

Nitric oxide induces rapid, calcium-dependent release of vesicular glutamate and ATP from cultured rat astrocytes

Nitric oxide (NO; 1 microM) or an NO donor (500 microM diethylenetriamine-nitric oxide, DETA-NONOate) caused rapid glutamate and ATP release from cultured rat cortical astrocytes. NO-induced glutamate release was prevented by calcium chelators (EGTA or BAPTA-AM) and an inhibitor of vesicular exocytosis (botulinum neurotoxin C, BoTx-C), but not by a glutamate transport inhibitor, L-trans-pyrrolidine-2,4-dicarboxylate (t-PDC), a cyclooxygenase inhibitor (indomethacin), or an inhibitor of soluble guanylate cyclase 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), and was not induced by mitochondrial respiratory inhibitors (myxothiazol or azide). Similarly to glutamate, NO-induced ATP release was also completely blocked by BAPTA-AM and BoTx-C, suggesting again a vesicular, calcium-dependent mechanism of release. Addition of DETA-NONOate (500 microM) to fura-2-loaded astrocytes induced a rapid, transient increase in intracellular calcium levels followed by a lower, sustained level of calcium entry. The latter was blocked by gadolinium (1 microM), an inhibitor of capacitative Ca(2+) entry. Thus, NO appears to cause rapid exocytosis of vesicular glutamate and ATP from astrocytes by raising intracellular calcium levels. Astrocytes activated by lipopolysaccharide/endotoxin and interferon-gamma to express inducible NO synthase (iNOS) maintained substantially higher extracellular glutamate levels than nonactivated cells or activated cells treated with an iNOS inhibitor (1400W), but the rate of glutamate uptake by these cells was similar. This suggests that NO from inflammatory-activated astrocytes causes release of astrocytic glutamate. NO-induced release of astrocytic glutamate and ATP may be important in physiological or pathological communication between astrocytes and neurons.

Biochemical characterization of desloratadine, a potent antagonist of the human histamine H(1) receptor

We have characterized desloratadine (5H-benzo[5,6]cyclohepta[1,2-b]pyridine, 8-chloro-6,11-dihydro-11-(4-piperidinylidene), CAS 100643-71-8) as a potent antagonist of the human histamine H(1) receptor. [3H]Desloratadine bound to membranes expressing the recombinant human histamine H(1) receptor in Chinese hamster ovary cells (CHO-H(1)) in a specific and saturable manner with a K(d) of 1.1+/-0.2 nM, a B(max) of 7.9+/-2.0 pmol/mg protein, and an association rate constant of 0.011 nM(-1) x min(-1). The K(d) calculated from the kinetic measurements was 1.5 nM. Dissociation of [3H]desloratadine from the human histamine H(1) receptor was slow, with only 37% of the binding reversed at 6 h in the presence of 5 microM unlabeled desloratadine. Seventeen histamine H(1)-receptor antagonists were evaluated in competition-binding studies. Desloratadine had a K(i) of 0.9+/-0.1 nM in these competition studies. In CHO-H(1) cells, histamine stimulation resulted in a concentration-dependent increase in [Ca(2+)](i) with an EC(50) of 170+/-30 nM. After a 90-min preincubation with desloratadine, the histamine-stimulated increase in [Ca(2+)](i) was shifted to the right, with a depression of the maximal response at higher concentrations of antagonist. The apparent K(b) value was 0.2+/-0.14 nM with a slope of 1.6+/-0.1. The slow dissociation from the receptor and noncompetitive antagonism suggests that desloratadine may be a pseudoirreversible antagonist of the human histamine H(1) receptor. The mechanism of desloratadine antagonism of the human histamine H(1) receptor may help to explain the high potency and 24-h duration of action observed in clinical studies.

Natriuretic peptide system in fetal heart and circulation

Atrial natriuretic peptide, brain natriuretic peptide and C-type natriuretic peptide belong to a family of hormones that have diuretic, natriuretic and vasodepressor activity and play a part in pressure and volume homeostasis in adults. As little is known about the natriuretic peptides during cardiac maturation, this review summarizes current knowledge about the early expression of components of the natriuretic peptide system in the heart during embryonic and fetal development. The data indicate a functional importance of the fetal natriuretic peptide system, especially under pathophysiological conditions. Thus, in the fetus, the system fulfils important beneficial compensatory roles in cardiovascular disease, rather than in day-to-day pressure and volume homeostasis. In comparison with data on the relevance of natriuretic peptides in adults, those summarized here indicate a functional maturation of the natriuretic peptide system during ontogeny in mammals.

Histamine-induced calcium entry in rat cerebellar astrocytes: evidence for capacitative and non-capacitative mechanisms

We have investigated the effects of histamine on the intracellular calcium concentration ([Ca2+]i) of cultured rat cerebellar astrocytes using fura-2-based Ca2+ imaging microscopy. Most of the cells responded to the application of histamine with an increase in [Ca2+]i which was antagonized by the H1 receptor blocker mepyramine. When histamine was applied for several minutes, the majority of the cells displayed a biphasic Ca2+ response consisting of an initial transient peak and a sustained component. In contrast to the initial transient [Ca2+]i response, the sustained, receptor-activated increase in [Ca2+]i was rapidly abolished by chelation of extracellular Ca2+ or addition of Ni2+, Mn2+, Co2+ and Zn2+, but was unaffected by nifedipine, an antagonist of L-type voltage-activated Ca2+ channels. These data indicate that the sustained increase in [Ca2+]i was dependent on Ca2+ influx. When intracellular Ca2+ stores were emptied by prolonged application of histamine in Ca2+-free conditions, Ca2+ re-addition after removal of the agonist did not lead to an 'overshoot' of [Ca2+]i indicative of store-operated Ca2+ influx. However, Ca2+ stores were refilled despite the absence of any substantial change in the fura-2 signal. Depletion of intracellular Ca2+ stores using cyclopiazonic acid in Ca2+-free saline and subsequent re-addition of Ca2+ to the saline resulted in an increase in [Ca2+]i that was significantly enhanced in the presence of histamine. The results suggest that besides capacitative mechanisms, a non-capacitative, voltage-independent pathway is involved in histamine-induced Ca2+ entry into cultured rat cerebellar astrocytes.

Signalling pathway for histamine activation of non-selective cation channels in equine tracheal myocytes

1. The signalling pathway underlying histamine activation of non-selective cation channels was investigated in single equine tracheal myocytes. Application of histamine (100 microM) activated the transient calcium-activated chloride current (ICl(Ca)) and sustained, low amplitude non-selective cation current (ICat). The H1 receptor antagonist pyrilamine (10 microM) blocked activation of ICl(Ca) and ICat. Simultaneous application of histamine (100 microM) and caffeine (8 mM) during H1 receptor blockade activated ICl(Ca), but not ICat. Neither the H2 receptor antagonist cimetidine (20 microM) nor the H3 receptor antagonist thioperamide (20 microM) prevented activation of ICl(Ca) and ICat. 2. Intracellular dialysis of anti-Galphai/Galphao antibodies completely blocked activation of ICat by histamine, whereas ICl(Ca) was not affected. By contrast, anti-Galphaq/Galpha11 antibodies greatly inhibited ICl(Ca), but did not alter activation of ICat. 3. 1-Oleoyl-2-acetyl-sn-glycerol (OAG, 20-100 microM) did not induce any current or affect currents activated by histamine or methacholine (mACH). Simultaneous application of OAG and caffeine activated ICl(Ca), but not ICat, indicating that a rise in [Ca2+]i and stimulation of diacylglycerol-sensitive protein kinase C (PKC) is not sufficient to activate ICat. The phospholipase C inhibitor U73122 (2 microM) blocked histamine activation of ICl(Ca) and ICat, but simultaneous exposure of myocytes to histamine and caffeine restored both ICl(Ca) and ICat in the presence of U73122. 4. Histamine and mACH activated currents with equivalent I-V relationships. The currents activated by these agonists were not additive; following activation of ICat by mACH, histamine failed to induce an additional membrane current. Similarly, mACH did not induce an additional current after full activation of ICat by histamine. 5. We conclude that H1 histamine receptors activate ICat through coupling to Gi/Go proteins. Activation of ICat also requires intracellular calcium release, mediated by H1 receptors coupling to Gq/G11 proteins. This coupling is analogous to the activation of ICat by co-stimulation of M2 and M3 receptors.

Inhibition of bradykinin-induced phosphoinositide hydrolysis and Ca2+ mobilisation by phorbol ester in rat cultured vascular smooth muscle cells

Regulation of the increase in inositol phosphate (IP) production and intracellular Ca2+ concentration ([Ca2+]i by protein kinase C (PKC) was investigated in cultured rat vascular smooth muscle cells (VSMCs). Pretreatment of VSMCs with phorbol 12-myristate 14-acetate (PMA, 1 microM) for 30 min almost abolished the BK-induced IP formation and Ca2+ mobilisation. This inhibition was reduced after incubating the cells with PMA for 4 h, and within 24 h the BK-induced responses were greater than those of control cells. The concentrations of PMA giving a half-maximal (pEC50) and maximal inhibition of BK induced an increase in [Ca2+]i, were 7.8 +/- 0.3 M and 1 microM, n = 8, respectively. Prior treatment of VSMCs with staurosporine (1 microM), a PKC inhibitor, inhibited the ability of PMA to attenuate BK-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. Paralleling the effect of PMA on the BK-induced IP formation and Ca2+ mobilisation, the translocation and downregulation of PKC isozymes were determined by Western blotting with antibodies against different PKC isozymes. The results revealed that treatment of the cells with PMA for various times, translocation of PKC-alpha, betaI, betaII, delta, epsilon, and zeta isozymes from the cytosol to the membrane were seen after 5 min, 30 min, 2 h, and 4 h of treatment. However, 24-h treatment caused a partial downregulation of these PKC isozymes in both fractions. Treatment of VSMCs with 1 microM PMA for either 1 or 24 h did not significantly change the K(D) and Bmax of the BK receptor for binding (control: K(D) = 1.7 +/- 0.2 nM; Bmax = 47.3 +/- 4.4 fmol/mg protein), indicating that BK receptors are not a site for the inhibitory effect of PMA on BK-induced responses. In conclusion, these results demonstrate that translocation of PKC-alpha, betaI, betaII, delta, epsilon, and zeta induced by PMA caused an attenuation of BK-induced IPs accumulation and Ca2+ mobilisation in VSMCs.

Regulation of 5-hydroxytryptamine-induced signal transduction in canine cultured aorta smooth muscle cells by phorbol ester

Regulation of the increase in inositol phosphates (IPs) production and intracellular Ca2+ concentration ([Ca2+]i) by protein kinase C (PKC) was investigated in cultured canine aorta smooth muscle cells (ASMCs). Stimulation of ASMCs by 5-hydroxytryptamine (5-HT) led to IPs formation and caused an initial transient [Ca2+]i peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner. Pretreatment of ASMCs with phorbol 12-myristate 13-acetate (PMA) for 30 min almost abolished the 5-HT-induced IPs formation and Ca2+ mobilization. This inhibition was reduced after long-term incubating the cells with PMA. Prior treatment of ASMCs with staurosporine or GF109203X, PKC inhibitors, inhibited the ability of PMA to attenuate 5-HT-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. In parallel with the effect of PMA on the 5-HT-induced IP formation and Ca2+ mobilization, the translocation and down-regulation of PKC isozymes were determined by Western blotting with antibodies against different PKC isozymes. The results revealed that treatment of ASMCs with PMA for various times, translocation of PKC-alpha, betaI, betaII, delta, epsilon, theta, and zeta isozymes from the cytosol to the membrane was seen after 5-min, 30-min, 2-h, and 4-h treatment. However, 24-h treatment caused a partial down-regulation of these PKC isozymes. In conclusion, these results demonstrate that translocation of PKC-alpha, betaI, betaII, delta, epsilon, theta, and zeta induced by PMA caused an attenuation of 5-HT-induced IPs accumulation and Ca2+ mobilization in ASMCs.

Histamine sensitivity of mesenteric afferent nerves in the rat jejunum

The concept of functional interaction between mast cells and intestinal afferents is gaining support. We have therefore characterized the action of histamine on jejunal afferent discharge in the anesthetized rat. Whole nerve mesenteric afferent discharge was recorded in conjunction with intestinal pressure in response to a range of histamine agonists and antagonists. Histamine at 2, 4, and 8 micromol/kg (iv) evoked a dose-dependent biphasic increase in afferent discharge together with a biphasic rise in intestinal pressure. However, these two events were mediated independently, since nifedipine (1 mg/kg) substantially reduced the intestinal pressure increase but not the afferent discharge. These responses were completely inhibited by pyrilamine (5 mg/kg) but unaffected by ranitidine (5 mg/kg) or thioperamide (2 mg/kg). Neither the selective H2 receptor agonist dimaprit nor the selective H3 receptor agonist R-alpha-methylhistamine caused any modulation of afferent discharge. We conclude that histamine stimulates an H1 receptor-mediated increase in mesenteric afferent discharge that is independent of intestinal motor events. This suggests that histamine potentially acts as a mediator in mast cell-to-afferent nerve communication in the small intestine.

Uncoupling of bradykinin-induced phosphoinositide hydrolysis and Ca2+ mobilization by phorbol ester in canine cultured tracheal epithelial cells

1. Regulation of the increase in inositol phosphates (IPs) production and intracellular Ca2+ concentration ([Ca2+]i by protein kinase C (PKC) was investigated in canine cultured tracheal epithelial cells (TECs). Stimulation of TECs by bradykinin (BK) led to IPs formation and caused an initial transient [Ca2+]i peak in a concentration-dependent manner. 2. Pretreatment of TECs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min attenuated the BK-induced IPs formation and Ca2+ mobilization. The maximal inhibition occurred after incubating the cells with PMA for 2 h. 3. The concentrations of PMA that gave half-maximal (pEC50) inhibition of BK-induced IPs accumulation and an increase in [Ca2+]i were 7.07 M and 7.11 M, respectively. Inactive phorbol ester, 4alpha-phorbol 12,13-didecanoate at 1 microM, did not inhibit these responses. Prior treatment of TECs with staurosporine (1 microM), a PKC inhibitor, inhibited the ability of PMA to attenuate BK-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. 4. In parallel with the effect of PMA on the BK-induced IPs formation and Ca2+ mobilization, the translocation and down-regulation of PKC isozymes were determined. Analysis of cell extracts by Western blotting with antibodies against different PKC isozymes revealed that TECs expressed PKC-alpha, betaI, betaII, gamma, delta, epsilon, theta and zeta. With PMA treatment of the cells for various times, translocation of PKC-alpha, betaI, betaII, gamma, delta, epsilon and theta from cytosol to the membrane was seen after 5 min, 30 min, 2 h, and 4 h treatment. However, 6 h treatment caused a partial down-regulation of these PKC isozymes. PKC-zeta was not significantly translocated and down-regulated at any of the times tested. 5. Treatment of TECs with 1 microM PMA for either 30 min or 6 h did not significantly change the KD, and Bmax receptor for BK binding (control: KD=1.7+/-0.3 nM; Bmax=50.5+/-4.9 fmol/mg protein), indicating that BK receptors are not a site for the inhibitory effect of PMA on BK-induced responses. 6. In conclusion, these results suggest that activation of PKC may inhibit the phosphoinositide hydrolysis and consequently attenuate the [Ca2+]i increase or inhibit independently both responses to BK. The translocation of pKC-alpha, betaI, betaII, delta, epsilon, gamma, and theta induced by PMA caused an attenuation of BK-induced IPs accumulation and Ca2+ mobilization in TECs.

Effects of mitogen-activated protein kinase kinase inhibitor PD 098059 on antigen challenge of guinea-pig airways in vitro

1. It has been shown that activation of protein tyrosine kinases is the earliest detectable signalling response to FcepsilonRI cross-linking on mast cell. Following tyrosine kinase activation, a family of mitogen-activated protein kinases (MAPKs) was found to be activated as well. The present study examined the role of MAPK signalling cascade in in vitro model of allergic asthma using a specific MAPK kinase inhibitor PD 098059. 2. Guinea-pigs were passively sensitized with IgG antibody raised against ovalbumin (OA). Effects of PD 098059 on OA-induced anaphylactic contraction of isolated bronchi and release of histamine and peptidoleukotrienes from chopped lung preparations were studied. 3. PD 098059 (10-50 microM) produced only minor reduction of maximal OA-induced bronchial contraction. In contrast, the rate of relaxation of OA-induced bronchial contraction was markedly faster in the presence of PD 098059 than the vehicle control in a concentration-dependent manner. 4. These observations corroborate well with the inability of PD 098059 (5-50 microM) to substantially block the OA-induced release of histamine and with marked inhibition of OA-induced release of peptidoleukotrienes from lung fragments in the presence of PD 098059. Exogenous arachidonic acid-induced release of peptidoleukotrienes from lung fragments was not blocked by PD 098059. 5. In immunoblotting study, we found that p42MAPK was constitutively expressed in guinea-pig bronchi. However, treatment with OA, histamine or LTD4 did not cause activation of p42MAPK. These findings together with the lack of inhibitory effects of PD 098059 on bronchial contraction induced by histamine or LTD4 suggest that histamine- and LTD4-induced bronchial contractions are not mediated by p42MAPK activation. 6. Taken together, our findings show that inhibition of MAPK signalling cascade by PD 098059 significantly reduced the OA-triggered release of peptidoleukotrienes leading to rapid relaxation of anaphylactic bronchial contraction. On the other hand, p42MAPK did not play a role in histamine- or LTD4-induced bronchial smooth muscle contraction suggesting that PD 098059 exerts its inhibitory effects on OA-induced bronchial contraction primarily through inhibition of peptidoleukotrienes release from mast cells.

Protein kinase C induced changes in human airway smooth muscle tone: the effects of Ca2+ and Na+ transport

Activation of protein kinase C by phorbol 12,13-dibutyrate (PDB) (1 nM-3 microM) caused a concentration-dependent contractile response in human isolated bronchus. The mean maximal contraction was 26 +/- 4.4% (n = 11) of that induced by acetylcholine (1 mM). The contraction was increased by the presence of the Ca2+ ionophore (A23187) to 47 +/- 6% (n = 7, P < 0.05) by the Ca2+ channel agonist, Bay K 8644 to 59.5 +/- 4.5% (n = 4, P < 0.05) and by KCl to 47.4 +/- 6%, while it was unaffected by carbachol (28.7 +/- 6.8%, n = 4, P > 0.05). The Ca2+ channel antagonist, verapamil (1 microM) significantly reduced the contraction from 32.3 +/- 4.9 to 12.5 +/- 1% (n = 4, P < 0.05) and in the presence of nifedipine (1 microM), the contractile response was abolished. A single concentration of 10 microM PDB produced a biphasic response-relaxation (6 +/- 1%) followed by contraction (76 +/- 4%, n = 4) which was greater than that produced when responses were obtained cumulatively. The relaxation response was inhibited by the addition of a Na-/K+ exchange antagonist, ouabain (10 microM) which also markedly potentiated the contractile response to 110 +/- 10% (n = 4, P < 0.05). These results suggest that the protein kinase C-mediated contraction in human airway smooth muscle is dependent on extracellular Ca2+ influx. Protein kinase C may also phosphorylate Na+/K(+)-ATPase resulting in a relaxation response.

Physiological perspectives of therapy in bronchial hyperreactivity

PURPOSE

This paper reviews the literature on the aetiology and therapy of bronchial hyperreactivity to describe the underlying pathophysiology, identify patients at risk and update knowledge on new and existing therapies.

SOURCE

Information was obtained from monograms on New Drugs for Asthma, Respiratory Medicine: recent advances, Agents and Actions Supplements, Pulmonary Pharmacology, Anesth Analg, the European Journal of Respiration and a Medline literature search.

PRINCIPAL FINDINGS

Reduced airway calibre, increased bronchial contractility, altered permeability of the bronchial mucosa, humoral and cellular mediators, and dysfunctional neural regulation are critical factors for bronchial hyperreactivity, a characteristic feature of hyperreactive airways which results in bronchoconstriction after exposure to varied stimuli. Preoperative anaesthetic considerations in these patients include FEV1 and PEFR testing to assess the severity and for optimal control of the condition. Bronchospasm causing hypoxaemia is the major intraoperative problem anticipated in these patients. Current therapeutic management of bronchoconstriction focuses on the beta 2 agonists, theophylline and steroids. Besides relaxing the airway smooth muscle these agents are all capable of altering bronchial inflammatory responses. Future developments of therapy are directed towards the inflammatory components of the disease.

CONCLUSION

This review has presented background information on physiological mechanisms of smooth muscle contractility, pathophysiological alterations of bronchial contractility and the pharmacological basis of therapy in bronchoconstrictive disease. Information is presented to enable the prompt arrest and reversal of airway constriction, and to maintain prophylactic treatment during the perioperative period. Intraoperative bronchospasm is managed by adequate oxygenation and reversal of bronchoconstriction.

Expression and function of voltage-dependent potassium channel genes in human airway smooth muscle

Patch clamp and RNA-polymerase chain reaction methods were used to determine the expression of voltage-dependent potassium channel currents and mRNAs in human airway smooth muscle cells, and tension measurements were used to examine the functional role of specific potassium channel gene products in human bronchial smooth muscle. RNA from airway smooth muscle tissue revealed the presence of Kv1.2 (11 kilobases (kb)) and Kv1.5 (3.5 and 4.4 kb) transcripts, as well as Kv1.1 mRNA (9.5 kb), which has not previously been reported in smooth muscle; transcripts from other gene families were not detected. RNA-polymerase chain reaction from cultured human myocytes confirmed that the identified transcripts were expressed by smooth muscle cells. The available voltage-dependent potassium current in human airway myocytes was insensitive to charybdotoxin (200 nM) but blocked by 4-aminopyridine. Dendrotoxin (1-300 nM; inhibits Kv1.1 and Kv1.2 channels), charybdotoxin (10 nM to 1 microM; inhibits KCa and Kv1.2 channels), and glybenclamide (0.1-100 microM; inhibits KATP channels) had no effect on resting tone. Conversely, 4-aminopyridine increased resting tension with an EC50 (1.8 mM) equivalent to that observed for current inhibition (1.9 mM). Human airway myocytes express mRNA from several members of the Kv1 gene family; the channel that underlies the predominate voltage-dependent current and the regulation of basal tone appears to be Kv1.5.

Calcium mobilization and isometric tension in bovine tracheal smooth muscle: effects of salbutamol and histamine

We determined if decreases in relative free intracellular calcium concentration ([Ca2+]i) caused by salbutamol, a selective beta2-adrenoreceptor agonist, were paralleled by calcium egression from the cytosol in bovine trachealis muscle strips. [Ca2+]i, or tissue-surface extracellular calcium changes (Ts[Ca2+]ext), were monitored using Fluo-3 acetoxymethylester or Fluo-3 pentaammonium salt simultaneously with isometric tension. Salbutamol (1 microM) decreased histamine-induced isometric tension from an average peak tension of 128.5 +/- 18.4 to -4.9 +/- 0.3 mN/mm2, and reduced the associated sustained increases in [Ca2+]i from 100% at peak to 20.4 +/- 7.6%. Both histamine-induced elevation in [Ca2+]i and isometric tension were reversed completely by forskolin (1 microM). In muscle strip at active resting tension, salbutamol caused a decrease (49.6 +/- 12.1%) in [Ca2+]i. Following precontraction with histamine, salbutamol caused an immediate and sustained increase in Ts[Ca2+]ext which was not seen in a Na(+)-free solution. Finally, propranolol (10 microM) blocked both increases in Ts[Ca2+]ext and muscle relaxation caused by salbutamol. These findings indicate that in bovine trachealis muscle, the effect of salbutamol to decrease [Ca2+]i and isometric tension is via a beta2-adrenoceptor, and the changes in [Ca2+]i are by an increase in calcium egression via the Na(+)/Ca2+ exchanger, and reuptake by myoplasmic stores.

Effects of phorbol 12,13-diacetate and its influence on spasmogenic responses in normal and sensitized guinea-pig trachea

We have studied the effects of phorbol 12,13-diacetate (PDA) and its influence on a variety of spasmogenic responses in trachea isolated from normal and sensitized guinea-pigs. Tracheal preparations were denuded of epithelium, treated with indomethacin (2.8 microM), and cooled to 20 degrees C. In these experimental conditions, tracheal strips contracted to PDA (0.1 nM-1 microM). Contractions to PDA (1 microM) were greater in sensitized tissues. In normal trachea, contractions to PDA (0.1 microM) were depressed by H-7, 1-(5-isoquinolinyl-sulphonyl)-2-methylpiperazine, (50 microM), amiloride (10 microM), verapamil (10 microM) and Ca(2+)-free exposure. Similar effects were obtained in sensitized trachea except that PDA-induced contraction was resistant to verapamil and Ca(2+)-free exposure. Cooling (20 degrees C) of normal trachea substantially depressed the response to CaCl2 (in K(+)-depolarized tissues), KCl, histamine and 5-hydroxytryptamine without affecting the spasm induced by acetylcholine. This inhibitory effect of cooling was not observed in sensitized trachea. PDA (0.1 microM) did not affect spasmogenic responses at 37 degrees C but counteracted the inhibitory effect of cooling in normal trachea. PDA had no effect on sensitized tissues. PDA (0.1-1 microM) did not alter Ca(2+)-induced contraction of skinned normal and sensitized trachea. These results support the hypothesis that intracellularly stored Ca2+ plays an important role in the activation of sensitized tracheal muscle.

Histamine antagonizes serotonin and growth factor-induced mitogen-activated protein kinase activation in bovine tracheal smooth muscle cells

We examined the effects of the bronchoconstrictor agonists serotonin (5-hydroxytryptamine; 5-HT) and histamine on mitogen-activated protein (MAP) kinase activation in cultured bovine tracheal myocytes. Kinase renaturation assays demonstrated activation of the 42- and 44-kDa MAP kinases within 2 min of 5-HT exposure. MAP kinase activation was mimicked by alpha-methyl-5-HT and reduced by pretreatment with either phorbol 12,13-dibutyrate or forskolin, suggesting activation of the 5-HT2 receptor, protein kinase C, and Raf-1, respectively. Raf-1 activation was confirmed by measurement of Raf-1 activity, and the requirement of Raf-1 for 5-HT-induced MAP kinase activation was demonstrated by transient transfection of cells with a dominant-negative allele of Raf-1. Histamine pretreatment significantly inhibited 5-HT and insulin-derived growth factor-1-induced MAP kinase activation. Attenuation of MAP kinase activation was reversed by cimetidine, mimicked by forskolin, and accompanied by cAMP accumulation and inhibition of Raf-1, suggesting activation of the H2 receptor and cAMP-dependent protein kinase A. However, histamine treatment inhibited Raf-1 but not MAP kinase activation following treatment with either platelet-derived growth factor or epidermal growth factor, implying a Raf-1-independent MAP kinase activation pathway. In summary, our data suggest a model whereby 5-HT activates MAP kinase via a protein kinase C/Raf-1 pathway, and histamine attenuates MAP kinase activation by serotonin via activation of cAMP-dependent protein kinase A and inhibition of Raf-1.

Inhibitory effect of phorbol ester on bradykinin-induced phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells

Regulation of the increase in inositol 1,4,5-trisphosphate (IP3) production and intracellular Ca2+ concentration ([Ca2+]i) by protein kinase C (PKC) was investigated in cultured canine tracheal smooth muscle cells (TSMCs). Stimulation of TSMCs by bradykinin (BK) led to IP3 formation and caused an initial transient peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner. Pretreatment of TSMCs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min blocked the BK-induced IP3 formation and Ca2+ mobilization. However, this inhibition was reduced after incubating the cells for 4 h with PMA. Inactive phorbol ester, 4 alpha-phorbol 12,13-didecanoate at 1 microM, did not inhibit these responses to BK. Prior treatment with staurosporine (1 microM), a PKC inhibitor, inhibited the effect of PMA on the BK-induced response, suggesting that the effect of PMA is mediated by the activation of PKC. In parallel experiments, a change of PKC activity was observed. PMA rapidly decreased PKC activity in the cytosol of TSMCs, while increasing it transiently in the cell membranes within 30 min. Thereafter the membrane-associated PKC activity decreased and persisted for at least 24 h of PMA treatment. Moreover, treatment with 1 microM PMA for 2 and 24 h did not significantly change the KD and Bmax of the BK receptor for [H]BK binding (control: KD = 2.3 +/- 0.3 nM, Bmax = 25.2 +/- 1.4 fmol/mg protein). These results suggest that activation of PKC inhibit IP3 accumulation and consequently attenuate [Ca2+]i increase or inhibit independently both responses. The PMA-induced inhibition of responses to BK was associated with an increase in membranous PKC activity.

Inhibitory Effect of Phorbol Ester on Carbachol-Induced Signal Transduction in Cultured Canine Tracheal Smooth Muscle Cells

Regulation of the increases in inositol 1,4,5-trisphosphate (IP(3)) production and intracellular Ca(2+) concentration ([Ca(2+)](i)) by activation of protein kinase C (PKC) was investigated in cultured canine tracheal smooth muscle cells (TSMCs). Stimulation of TSMCs by carbachol led to IP(3) formation and caused an initial transient peak of [Ca(2+)](i) followed by a sustained elevation in a concentration-dependent manner. Pretreatment of TSMCs with phorbol 12-myristate 13-acetate (PMA, 1 &mgr;M) for 30 min blocked the carbachol-induced IP(3) formation and Ca(2+) mobilization. Following preincubation, carbachol-induced Ca(2+) mobilization recovered within 24 h. The concentrations of PMA that gave half-maximal inhibition of carbachol-induced IP(3) formation and increase in [Ca(2+)](i) were 7 and 4 nM, respectively. Prior treatment of TSMCs with staurosporine (1 &mgr;M), a PKC inhibitor, inhibited the ability of PMA to attenuate carbachol-induced responses. Inactive phorbol ester, 4alpha-phorbol 12,13-didecanoate at 1 &mgr;M, did not inhibit these responses to carbachol. The K(d) and B(max) of the muscarinic receptor for [(3)H]N-methylscopolamine binding were not significantly changed by PMA treatment. PMA also decreased PKC activity in the cytosol of TSMCs, while increasing it transiently in the membranes within 30 min. Thereafter, the membrane-associated PKC activity decreased and persisted for at least 24 h of PMA treatment. Taken together, these results suggest that activation of PKC may inhibit phosphoinositide hydrolysis and consequently attenuate the [Ca(2+)](i) increase or inhibit both responses independently. The inhibition by PMA of carbachol-induced responses was inversely correlated with membranous PKC activity. Copyright 1995 S. Karger AG, Basel

Feedforward control of agonist-induced Ca2+ signalling by protein kinase C in airway smooth muscle cells

In isolated bovine tracheal smooth muscle cells, the potent and specific protein kinase C inhibitor GF 109203X caused an inhibition of methacholine-and histamine-induced Ca2+ mobilization and influx, indicating for the first time that protein kinase C activation induced by contractile agonists exerts a positive feedforward control of Ca2+ signalling by these agonists.

Molecular pharmacological aspects of histamine receptors

In this article, we review the recent developments in the field of histamine research. Besides the description of pharmacological tools for the H1, H2 and H3 receptor, specific attention is paid to both the molecular aspects of the receptor proteins, including the recent cloning of the receptor genes, and their respective signal transduction mechanisms.

Effects of phenylephrine induced increase in arterial pressure and closure of the ductus arteriosus on the secretion of atrial natriuretic peptide (ANP) and renin in the ovine fetus

Although atrial natriuretic peptide (ANP) has been detected in the plasma of late gestation fetal sheep, stimuli that control its secretion and its function in regulating fluid volume are unclear. To determine stimuli that increase ANP secretion and to ascertain whether the response is a function of gestation we studied 20 chronically cannulated fetal sheep. The fetuses were divided into 3 groups; Group I (age range 118-129 days), Group II (age range 129-141 days) and Group III (age range 127-137 days) gestation. Arterial pressure was increased to within a physiologic range by infusing phenylephrine at 6 micrograms/min at 0.1 ml/min into the inferior vena cava of the fetus (Groups I and II). Corrected for body weight fetuses in Group I received 2 micrograms/kg/min whereas fetuses in Group II received 1.66 micrograms/kg/min. In the fetuses in Group III preload to the right side of the heart was increased by inflating an occluder cuff was placed around the ductus arteriosus. Systemic mean arterial pressure (MAP) increased significantly in fetuses in Groups I and II. Plasma ANP concentrations increased significantly in all fetuses. Plasma Renin Activity (PRA) decreased significantly in the fetuses in Group II. These results suggest that phenylephrine infusion and closure of the ductus arteriosus in utero increase circulating ANP in fetal sheep.

Intrauterine exposure to cocaine increased plasma ANP (atrial natriuretic peptide) but did not alter hypoxanthine concentrations in the sheep fetus

To assess the effects of cocaine, administered to the ewe, on the secretion of atrial natriuretic peptide (ANP), Plasma Renin Activity (PRA) and hypoxanthine in the fetus we studied 6 chronically cannulated sheep fetuses late in gestation. The ewe was given an intravenous injection of cocaine (2 mg/kg). Maternal and fetal arterial blood samples were withdrawn prior to the injection and at 2, 5, 10, 15, 45 and 60 min after the injection for the measurement of ANP, PRA and hypoxanthine. Fetal arterial blood pressure (MAP), plasma ANP and protein levels increased and pH and pO2 decreased after cocaine was administered to the ewe. Fetal plasma hypoxanthine and PRA did not change. These results suggest that cocaine administration to the ewe is associated with fetal hypertension, hypoxemia and acidemia all of which may serve as stimuli for the secretion of ANP.

The involvement of protein kinase C in the contraction of human airway smooth muscle

The involvement of protein kinase C in the contraction of airway smooth muscle has been investigated in human isolated bronchus. Phorbol 12,13-dibutyrate (PDB) (10 microM) produced aw biphasic response--relaxation followed by contraction. The protein kinase C inhibitor, staurosporine (0.1 microM) reduced the contractile response to PDB from 89 +/- 2.9% to 53 +/- 4.5% of the response to 1 mM acetylcholine (P < 0.05, n = 6) but increased the relaxation response from 12 +/- 6.1% to 29 +/- 5% (P < 0.05, n = 6). Staurosporine also reduced the maximal contractile response to a single dose of histamine (10 microM) from 121 +/- 13% to 91 +/- 10% (P < 0.05, n = 4) and the sustained phase tension from 94 +/- 4% to 85 +/- 5% at 30 min (P < 0.05, n = 4). However, GF 109203X, a more selective inhibitor of protein kinase C at 0.1 microM, 1 microM and 10 microM had no effect on the maximal contractile response and reduced only the sustained phase of the contraction to histamine. These results suggest that protein kinase C plays a role in maintenance of contraction in human airway smooth muscle.

Effect of phorbol ester on phosphoinositide hydrolysis and calcium mobilization induced by endothelin-1 in cultured canine tracheal smooth muscle cells

Regulation of the increase in inositol 1,4,5-trisphosphate (IP3) production and intracellular Ca2+ concentration ([Ca2+]i) by protein kinase C (PKC) was investigated in cultured canine tracheal smooth muscle cells (TSMCs). Stimulation of TSMCs by endothelin-1 (ET-1) led to IP3 formation and caused an initial transient peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner. Pretreatment of TSMCs with phorbol 12-myristate 13-acetate (PMA, 1 microM) for 30 min blocked the ET-1-induced IP3 formation and Ca2+ mobilization. However, this inhibition was reduced after incubating the cells for 8 h with PMA. Following preincubation, ET-1-induced Ca2+ mobilization recovered with time and reached the same extent of control cells within 48 h. The concentrations of PMA that gave half-maximal inhibition (-logEC50) of ET-1-induced IP3 formation and increase in [Ca2+]i were 8.6 and 8.4 M, respectively. Prior treatment of TSMCs with staurosporine (1 microM), a PKC inhibitor, inhibited the ability of PMA to attenuate ET-1-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. In parallel with the effect of PMA on the ET-1-induced IP3 formation and Ca2+ mobilization, a change of PKC activity was observed in TSMCs. PMA rapidly decreased PKC activity in the cytosol of TSMCs, while increasing it transiently in the membranes within 30 min. Thereafter the membrane-associated PKC activity decreased and persisted for at least 24 h of PMA treatment. Taken together, these results suggest that activation of PKC may inhibit the phosphoinositide hydrolysis and consequently attenuate the [Ca2+]i increase or inhibit independently both responses. The PMA-induced inhibition of responses to ET-1 was associated with an increase in membranous PKC activity.

A mannose receptor mediates mannosyl-rich glycoprotein-induced mitogenesis in bovine airway smooth muscle cells

The putative mannose receptor (MR), previously implicated in mannosyl-rich glycoprotein-induced mitogenesis in bovine airway smooth muscle (ASM) cells, was studied to determine its properties. Specific binding of the mitogenic neoglycoprotein, mannosylated bovine serum albumin (Man-BSA) to ASM cells was saturable, with an apparent Kd = 5.0 x 10(-8) M. Cell-bound ManBSA-colloidal gold conjugate was localized by electron microscopy to clathrin-coated pits on the cell surface, and was found to undergo internalization to endosomes; this was inhibitable by weak bases and swainsonine, that also inhibited ligand-induced mitogenesis. The ASM-MR, isolated by mannose-affinity chromatography, had the same apparent molecular mass as the macrophage (Mø) MR (M(r) = 175 kD), and was immunoprecipitated by an anti-MøMR immune serum. This antiserum blocked 125I-labeled-ManBSA binding to intact ASM cells, stimulated mitogenesis, and immunolocalized the ASM-MR in cytoplasmic vesicles compatible with endosomes. A monoclonal antibody directed against the MøMR also reacted with the ASM-MR; like the polyclonal antibodies, it stimulated mitogenesis as effectively as beta-hexosaminidases. These data indicate that the ASM-MR shares a number of functional and structural properties with the MøMR and suggest that similar receptors may have different main functions in different cells.

5-Hydroxytryptamine-stimulated calcium mobilization in cultured canine tracheal smooth muscle cells

5-Hydroxytryptamine (5-HT)-induced increase of intracellular Ca2+ concentration ([Ca2+]i) was monitored in cultured canine tracheal smooth muscle cells (TSMCs) using a fluorescent Ca2+ indicator Fura-2. Stimulation of TSMCs by 5-HT produced an initial transient peak followed by a sustained, concentration-dependent elevation of [Ca2+]i. The log (EC50) values of 5-HT for the peak and sustained plateau responses were -7.43 and -7.60 M, respectively. 5-HT1A and 5-HT3 receptor antagonists, NAN-190 and metoclopramide, inhibited the 5-HT-stimulated increase in [Ca2+]i with pKB values of 6.3 and 6.2, respectively, indicating that the 5-HT receptors mediating Ca2+ signal had low affinity for these receptor antagonists. In contrast, 5-HT2A receptor antagonists, ketanserin and mianserin, had high affinity in antagonizing the changes in [Ca2+]i response to 5-HT with pKB values of 8.3 and 8.3, respectively. The sustained elevation of [Ca2+]i was dependent on the presence of extracellular Ca2+. Removal of extracellular Ca2+ by addition of 2 mM EGTA during the sustained phase caused a rapid decline in [Ca2+]i to the resting level. In the absence of extracellular Ca2+, only an initial peak was observed which then declined to the resting level; the sustained elevation of [Ca2+]i could then be evoked by addition of 1.8 mM Ca2+ in the continued presence of 5-HT. Ca2+ influx was required for the changes of [Ca2+]i, since the Ca(2+)-channel blockers, diltiazem, verapamil, and Ni2+, decreased both the initial and sustained elevation of [Ca2+]i in response to 5-HT. These Ca(2+)-channel blockers also decreased the sustained elevation of [Ca2+]i when applied during the plateau phase. In conclusion, these findings indicate that the initial increase in [Ca2+]i stimulated by 5-HT acting on 5-HT2A receptors is due to the release of Ca2+ from internal stores, followed by the influx of external Ca2+ into the cells. The influx of extracellular Ca2+ partially involves a diltiazem and verapamil sensitive Ca2+ channel.

Bradykinin-stimulated calcium mobilization in cultured canine tracheal smooth muscle cells

Bradykinin (BDK)-induced increases in intracellular Ca2+ concentration ([Ca2+]i) were monitored in cultured canine tracheal smooth muscle cells (TSMCs) using a fluorescent Ca2+ indicator, Fura-2. BDK and kallidin caused an initial transient peak followed by a sustained elevation of [Ca2+]i in a concentration-dependent manner, with half-maximal stimulation (log EC50) obtained at -8.10 M and -8.04 M, respectively. The BDK-induced rise in [Ca2+]i was not affected by the BDK B1 receptor antagonist, des-Arg9[Leu8]-BDK (10 microM). However, the BDK B2 receptor antagonists des-Arg[Hyp3, Thi5,8, D-Phe7]-BDK and Hoe 140 had high affinity in antagonizing BDK with pKB values of 7.5 +/- 0.3 and 8.7 +/- 0.3, respectively. The sustained phase of the rise in [Ca2+]i was dependent on the presence of external Ca2+, as evidenced by a decline to the resting level on addition of EGTA. In the absence of external Ca2+, only an initial transient peak was seen which then declined to the resting level; a sustained elevation of [Ca2+]i could then be evoked by addition of 1.8 mM Ca2+ in the continued presence of BDK. Ca2+ influx was required for the changes in [Ca2+]i, since Ca(2+)-channel blockers, diltiazem, verapamil, and Ni2+, decreased both the initial and sustained elevation of [Ca2+]i in response to BDK. In conclusion, these findings indicate that the initial increase in [Ca2+]i stimulated by BDK acting on BDK B2 receptors is due to the release of Ca2+ from internal stores, followed by the influx of external Ca2+ into the cells. The influx of extracellular Ca2+ partially involves a diltiazem- and verapamil-sensitive Ca2+ channel.

Effect of phorbol ester on phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells

In cultured canine tracheal smooth muscle cells (TSMCs), muscarinic receptor stimulation led to phosphoinositide (PI) hydrolysis, formation of inositol phosphates (IPs), and mobilization of intracellular Ca2+. Desensitization of IPs accumulation and Ca2+ mobilization evoked by carbachol was investigated using [3H]inositol labelling and Ca(2+)-sensitive dye fura-2. Treatment of TSMCs with phorbol 12-myristate 13-acetate (PMA) for 30 min blocked the carbachol-stimulated formation of IPs and mobilization of Ca2+. The concentrations of PMA that gave half-maximal and maximal inhibition of carbachol-induced IPs accumulation were 70 nM and 1 microM, respectively. The inhibitory effect of PMA on carbachol-induced responses was reversed by staurosporine, a protein kinase C (PKC) inhibitor, suggesting that the inhibitory effect of PMA was mediated through the activation of PKC. Treatment of TSMCs with PMA for 24 h, the cells remained the ability to response to carbachol-induced IPs accumulation and Ca2+ mobilization with the same extent as that observed in the control group. Inactive phorbol ester, 4 alpha-phorbol 12, 13-didecanoate at 1 microM, did not inhibit the responses. The KD and Bmax of the muscarinic receptor for [3H]N-methyl scopolamine binding were not significantly changed by PMA treatment for either 30 min or 24 h. The locus of this inhibition was further investigated by examining the effect of PMA on AlF4(-)-stimulated IPs accumulation in canine TSMCs. AlF4(-)-induced response was inhibited by PMA treatment, supporting that G protein(s) can be directly activated by AlF4- which was uncoupled to phospholipase C (PLC) by PMA treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphoinositide metabolism in airway smooth muscle

Agonist-stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate, which generates inositol 1,4,5-trisphosphate and sn-1,2-diacylglycerol, is thought to be one of the major mechanisms underlying pharmacomechanical coupling in airway smooth muscle. This article is a review of the currently available information on phosphoinositide and inositol 1,4,5-trisphosphate metabolism in this tissue and includes data on inositol 1,4,5-trisphosphate-induced Ca2+ release and the receptor mediating this effect. The final section outlines the potential mechanisms underlying physiological regulation of phosphoinositide metabolism by other second-messenger pathways operative in this tissue.

5-Hydroxytryptamine receptor-mediated phosphoinositide hydrolysis in canine cultured tracheal smooth muscle cells

1. 5-Hydroxytryptamine (5-HT) has been shown to induce contraction of tracheal smooth muscle. However, the mechanisms of action of 5-HT are not known. We therefore investigated the effects of 5-HT on phospholipase C (PLC)-mediated phosphoinositide (PI) hydrolysis and its regulation in canine cultured tracheal smooth muscle cells (TSMCs) labelled with [3H]-inositol. 5-HT-induced inositol phosphates (IPs) accumulation was time- and dose-dependent with a half-maximal response (EC50) and a maximal response at 0.38 +/- 0.05 and 10 microM, respectively. 2. Ketanserin and mianserin (10 and 100 nM), 5-HT2 receptor antagonists, were equipotent in blocking the 5-HT-induced IPs accumulation with pKB values of 8.46 and 8.21, respectively. In contrast, the dose-response curves of 5-HT-induced IPs accumulation were not shifted until the concentrations of NAN-190 and metoclopramide (5-HT1A and 5-HT3 receptor antagonists, respectively) were increased up to 10 microM. 3. Pretreatment of TSMCs with pertussis toxin or cholera toxin did not inhibit the 5-HT-induced IPs accumulation, but partially inhibited the AlF(4-)-induced IPs response. 4. Stimulation of IPs accumulation by 5-HT required the presence of external Ca2+ and was blocked by EGTA. The addition of Ca2+ (3-620 nM) to digitonin-permeabilized TSMCs directly stimulated IPs accumulation. A further Ca(2+)-dependent increase in IPs accumulation was obtained by inclusion of either guanosine 5'-O-(3-thiotriphoshate) (GTP gamma S) or 5-HT. The combination of GTP gamma S and 5-HT elicited an additive effect on IPs accumulation. 5. Treatment with phorbol 12-myristate 13-acetate (PMA, 1 microM, 30 min) abolished the 5-HT-induced IPs accumulation. The concentrations of PMA that gave a half-maximal and maximal inhibition of 5-HT-induced IPs accumulation were 2.2 +/- 0.4 nM and 1 microM, n = 3, respectively. The protein kinase C (PKC) activator, 4 alpha-phorbol 12,13-didecanoate, at 1 microM, did not influence this response. The inhibitory effect of PMA was reversed by staurosporine, a PKC inhibitor, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. 6. The site of this inhibition was further investigated by examining the effect of PMA on AlF(4-)-induced IPs accumulation in canine TSMCs. AlF(4-)-stimulated IPs accumulation was inhibited by PMA treatment, suggesting that the effect of PMA is distal to the 5-HT receptor. 7. Acetylcholine-induced IPs accumulation was completely inhibited by atropine, but not affected by ketanserin or mianserin, suggesting that 5-HT-induced IPs accumulation is not due to release of acetylcholine.8. These results demonstrate that 5-HT directly stimulates PLC-mediated PI hydrolysis via a pertussis toxin- and cholera toxin-insensitive GTP binding protein in canine TSMCs and that this coupling process is negatively regulated by PKC. 5-HT2 receptors may be predominantly mediating IPs accumulation and presumably IP-induced Ca2+ release may function as the transducing mechanism for 5-HT stimulated contraction of tracheal smooth muscle.

Gene expression of atrial natriuretic factor in ovine fetal heart during development

OBJECTIVE

The present study quantified the abundance of atrial natriuretic factor (ANF) messenger RNA (mRNA) and determined the developmental pattern of ANF gene expression in the four cardiac chambers of the ovine fetus during the last two-thirds of gestation.

METHODS

Twenty-one fetuses from 13 time-dated pregnant ewes at gestational ages of 60-145 days were used for this study. Total RNA from fetal atria and ventricles was extracted and ANF mRNA was analyzed by Northern blotting. The ANF mRNA signal was quantified by light densitometry. The abundance of ANF mRNA in the cardiac chambers across gestational ages was analyzed by linear regression analysis and one-way analysis of variance.

RESULTS

Atrial natriuretic factor mRNA was much more abundant in the atria than in the ventricles of all fetuses at each gestational age studied. Atrial ANF mRNA levels were lowest in the younger fetuses at 60 days and increased with advancing gestation. Ventricular ANF mRNA levels were highest in fetuses at 60 days and decreased to almost nondetectable levels near term. No difference in ANF mRNA abundance was noted between the right and left atria or the right and left ventricles at each gestational age.

CONCLUSION

A developmental pattern of ANF gene expression is demonstrated in the ovine fetal heart during the last two-thirds of gestation. This pattern shows that atrial ANF mRNA abundance increases while ventricular abundance decreases as the fetus matures. Expression of the ANF gene in the fetal period may be regulated developmentally or induced by cardiovascular changes in utero.

Activation by histamine of bronchial epithelial cells from nonasthmatic subjects

Histamine is a major mediator of the mast cells that are present between epithelial cells in asthma. In asthma, there is an increased expression of ICAM-1 and HLA-DR and an increased spontaneous release of fibronectin. The effect of histamine was tested on bronchial epithelial cells obtained by bronchial brushing from 22 nonasthmatic subjects. The activation of epithelial cells was assessed by immunocytochemical analysis of the expression of membrane markers (ICAM-1 and HLA-DR) using the alkaline phosphatase-anti-alkaline phosphatase method and the release of fibronectin (enzyme immunoassay). Time-response (three experiments) and dose-response (six experiments) curves showed that the maximal effect was obtained after an incubation time of 24 h and a dose of 1 microM of histamine. For this time course and concentration, there was a highly significant increase in the number of cells expressing ICAM-1 (before histamine: 10 +/- 11%; after histamine: 32 +/- 20%; P < 0.001) and HLA-DR (before histamine: 8 +/- 7%; after histamine: 23 +/- 20%; P < 0.001) and in the release of fibronectin (before histamine: 30 +/- 20 ng/10(5) viable cells; after histamine: 61 +/- 35 ng/10(5) viable cells; P < 0.003). Cycloheximide blocked these effects, suggesting that histamine requires protein synthesis for its action. Pyrilamine (H1-blocker) and ranitidine (H2-blocker) at a concentration of 10 microM decreased the effect of histamine. However, there was no additive effect when both antagonists were added. This study suggests that mast cells present in the airways have a role in the activation of epithelial cells.