Homologous Desensitization Research Articles

Calcium signaling via two-pore channels: local or global, that is the question

Recently, we identified, for the first time, two-pore channels (TPCs, TPCN for gene name) as a novel family of nicotinic acid adenine dinucleotide phosphate (NAADP)-gated, endolysosome-targeted calcium release channels. Significantly, three subtypes of TPCs have been characterized, TPC1-3, with each being targeted to discrete acidic calcium stores, namely lysosomes (TPC2) and endosomes (TPC1 and TPC3). That TPCs act as NAADP-gated calcium release channels is clear, given that NAADP binds to high- and low-affinity sites associated with TPC2 and thereby induces calcium release and homologous desensitization, as observed in the case of endogenous NAADP receptors. Moreover, NAADP-evoked calcium signals via TPC2 are ablated by short hairpin RNA knockdown of TPC2 and by depletion of acidic calcium stores with bafilomycin. Importantly, however, NAADP-evoked calcium signals were biphasic in nature, with an initial phase of calcium release from lysosomes via TPC2, being subsequently amplified by calcium-induced calcium release (CICR) from the endoplasmic reticulum (ER). In marked contrast, calcium release via endosome-targeted TPC1 induced only spatially restricted calcium signals that were not amplified by CICR from the ER. These findings provide new insights into the mechanisms that cells may utilize to “filter” calcium signals via junctional complexes to determine whether a given signal remains local or is converted into a propagating global signal. Essentially, endosomes and lysosomes represent vesicular calcium stores, quite unlike the ER network, and TPCs do not themselves support CICR or, therefore, propagating regenerative calcium waves. Thus “quantal” vesicular calcium release via TPCs must subsequently recruit inositol 1,4,5-trisphoshpate receptors and/or ryanodine receptors on the ER by CICR to evoke a propagating calcium wave. This may call for a revision of current views on the mechanisms of intracellular calcium signaling. The purpose of this review is, therefore, to provide an appropriate framework for future studies in this area.

Involvement of canonical and non-canonical D1 dopamine receptor signalling pathways in L-dopa-induced dyskinesia

Chronic L-3,4-dihydroxyphenylalanine (L-dopa) treatment of Parkinson Disease (PD) often leads to debilitating involuntary movements, termed L-dopa-induced dyskinesia (LID). The past few years have seen an unprecedented increase in understanding the neural mechanisms underlying LID manifestation in PD associating them mostly with D1 dopamine (DA) receptor sensitisation and deregulated homologous desensitisation as well as hyperactivity of both canonical and non-canonical DA signalling pathways. We here review these recent findings and demonstrate that decreasing DA receptor-mediated signalling (i) by increasing D1 receptor internalization and (ii) by inhibiting the Ras-Extracellular signal-Regulated Kinase 1/2 non-canonical DA signalling cascade, might reduced LID severity. Strategy (i) uses the lentivirus-mediated over-expression of the G protein-coupled receptor kinase 6 that control the desensitisation of DA receptors. Strategy (ii) proposes to use statins that, besides being specific inhibitors of the rate-limiting enzyme in cholesterol biosynthesis, can also inhibit Ras isoprenylation and activity and subsequently the phosphorylation of ERK1/2. Experiments were performed in both the rodent and primate models of LID. Those results strongly suggest that different strategies might represent a treatment option for managing LID in PD.

Muscarinic Acetylcholine Receptor Modulation of Mu (μ) Opioid Receptors in Adult Rat Sphenopalatine Ganglion Neurons

The sphenopalatine ganglion (SPG) neurons represent the parasympathetic branch of the autonomic nervous system involved in controlling cerebral blood flow. In the present study, we examined the coupling mechanism between mu (mu) opioid receptors (MOR) and muscarinic acetylcholine receptors (mAChR) with Ca(2+) channels in acutely dissociated adult rat SPG neurons. Successful MOR activation was recorded in approximately 40-45% of SPG neurons employing the whole cell variant of the patch-clamp technique. In addition, immunofluorescence assays indicated that MOR are not expressed in all SPG neurons while M(2) mAChR staining was evident in all neurons. The concentration-response relationships generated with morphine and [d-Ala2-N-Me-Phe4-Glycol5]-enkephalin (DAMGO) showed IC(50) values of 15.2 and 56.1 nM and maximal Ca(2+) current inhibition of 26.0 and 38.7%, respectively. Activation of MOR or M(2) mAChR with morphine or oxotremorine-methiodide (Oxo-M), respectively, resulted in voltage-dependent inhibition of Ca(2+) currents via coupling with Galpha(i/o) protein subunits. The acute prolonged exposure (10 min) of neurons to morphine or Oxo-M led to the homologous desensitization of MOR and M(2) mAChR, respectively. The prolonged stimulation of M(2) mAChR with Oxo-M resulted in heterologous desensitization of morphine-mediated Ca(2+) current inhibition, and was sensitive to the M(2) mAChR blocker methoctramine. On the other hand, when the neurons were exposed to morphine or DAMGO for 10 min, heterologous desensitization of M(2) mAChR was not observed. These results suggest that in rat SPG neurons activation of M(2) mAChR likely modulates opioid transmission in the brain vasculature to adequately maintain cerebral blood flow.

Mechanism regulating proasthmatic effects of prolonged homologous β2-adrenergic receptor desensitization in airway smooth muscle

Use of long-acting beta(2)-adrenergic receptor (beta2AR) agonists to treat asthma incurs an increased risk of asthma morbidity with impaired bronchodilation and heightened bronchoconstriction, reflecting the adverse effects of prolonged homologous beta2AR desensitization on airway smooth muscle (ASM) function. Since phosphodiesterase 4 (PDE4) regulates ASM relaxation and contractility, we examined whether the changes in ASM function induced by prolonged homologous beta2AR desensitization are attributed to altered expression and action of PDE4. Cultured human ASM cells and isolated rabbit ASM tissues exposed for 24 h to the long-acting beta2AR agonist salmeterol exhibited impaired acute beta2AR-mediated cAMP accumulation and relaxation, respectively, together with ASM constrictor hyperresponsiveness. These proasthmatic-like changes in ASM function were associated with upregulated PDE4 activity due to enhanced expression of the PDE4D5 isoform and were prevented by pretreating the ASM preparations with the PDE4 inhibitor rolipram or with inhibitors of either PKA or ERK1/2 signaling. Extended studies using gene silencing and pharmacological approaches demonstrated that: 1) the mechanism underlying upregulated PDE4D5 expression following prolonged beta2AR agonist exposure involves PKA-dependent activation of G(i) protein signaling via its betagamma-subunits, which elicits downstream activation of ERK1/2 and its induction of PDE4D5 transcription; and 2) the induction of PDE4 activity and consequent changes in ASM responsiveness are prevented by pretreating the beta2AR agonist-exposed ASM preparations with inhibitors of G(i)-betagamma signaling. Collectively, these findings identify that the proasthmatic changes in ASM function resulting from prolonged homologous beta2AR desensitization are attributed to upregulated PDE4 expression induced by G(i)-betagamma-mediated cross-talk between the PKA and ERK1/2 signaling pathways.

A splice variant of the guanylyl cyclase-A receptor interferes with atrial natriuretic peptide (ANP) signaling

Background Activation of the homodimeric transmembrane guanylyl cyclase-A (GC-A) receptor upon binding of its extracellular ligands, atrial (ANP) and B-type (BNP) natriuretic peptides, leads to cyclic GMP formation in many types of cells. This NP/GC-A pathway has a critical role in the endocrine regulation of arterial blood pressure and volume and in the local counter-regulation of cardiac hypertrophy and fibrosis. Alterations of this system result in arterial hypertension, hypervolemia and cardiac hypertrophy. Many studies have shown that exposure of GC-A to high concentrations of ANP/BNP or to growth hormones such as angiotensin II (Ang II) or endothelin provokes homologous versus heterologous desensitization of the receptor [1]. However, the mechanisms accounting for this loss of function of GC-A in vivo are largely unknown. In the present study we identified and characterized a novel isoform of GC-A (GC-AΔLys-Gln 330) with unique structural properties. Our data reveal that this splice variant functions as dominant negative isoform and suggest that increased alternative splicing of GC-A may contribute to homologous or heterologous desensitization of the NP/GC-A system.

β-Arrestin 2 is required for the induction and strengthening of integrin-mediated leukocyte adhesion during CXCR2-driven extravasation

Leukocyte extravasation involves interdependent signaling pathways underlying the complex dynamics of firm adhesion, crawling, and diapedesis. While signal transduction by agonist-bound chemokine receptors plays a central role in the above responses, it is unclear how it contributes to the sustained and concurrent nature of such responses, given the rapid kinetics of chemokine-induced trimeric G protein coupling and homologous desensitization. Our findings unveil a novel role of beta-arrestins in regulating the activation of signaling pathways underlying discrete integrin-mediated steps in CXCR2-driven leukocyte extravasation. By combining in vivo approaches in beta-arrestin knockout mice with in vitro studies in engineered cellular models, we show that membrane-recruited beta-arrestin 2 is required for the onset and maintenance of shear stress-resistant leukocyte adhesion mediated by both beta(1) and beta(2) integrins. While both beta-arrestin isoforms are required for rapid keratinocyte-derived chemokine (KC)-induced arrest onto limiting amounts of vascular cell adhesion molecule-1 (VCAM-1), adhesion strengthening under shear is selectively dependent on beta-arrestin 2. The latter synergizes with phospholipase C in promoting activation of Rap1A and B, both of which co-operatively control subsecond adhesion as well as postarrest adhesion stabilization. Thus, receptor-induced Galpha(i) and beta-arrestins act sequentially and in spatially distinct compartments to promote optimal KC-induced integrin-dependent adhesion during leukocyte extravasation.

607 Caveolae-Dependent Internalization and Homologous Desensitization of VIP/PACAP Receptor, VPAC 2 in Gastrointestinal Smooth Muscle

607 Caveolae-Dependent Internalization and Homologous Desensitization of VIP/PACAP Receptor, VPAC 2 in Gastrointestinal Smooth Muscle

Epidermal growth factor induces lysophosphatidic acid type 1 receptor regulation through phosphorylation

Lysophosphatidic acid (LPA) is a local hormone/autacoid/ growth factor involved in many cellular responses such as: cell migration, proliferation and surviving, platelet aggregation, smooth muscle contraction, neurotransmitter release, establishment of focal adhesions, neurite retraction and cell rounding (among many others). The actions of LPA are mediated through a family of G protein coupled receptors (GPCRs) that includes five subtypes LPA1‐5 receptors which can couple to different G proteins. Phosphorylation of GPCRs is one of the earliest events that regulate their function. Current evidence indicates that homologous desensitization of these receptors mainly involves G protein‐coupled receptor kinases (GRKs), whereas in heterologous desensitization second messenger‐activated kinases play a key role. The primary goal of this work was to study the possibly regulation of LPA1 receptor induced by EGF receptor activation. The LPA1 receptor, tagged with the green fluorescent protein, was transfected into C9 cells. Stimulation with LPA induces an increase in intracellular calcium concentration, LPA1 receptor phosphorylation and internalization. Activation of EGF receptors decreases (50%) LPA‐induced intracellular calcium increase. In addition, EGF receptor activation also induced LPA1 receptor phosphorylation and internalization. This "crosstalk" seems to involve protein kinase C, since pharmacological inhibitors markedly decreased EGF‐induced LPA1 receptor phosphorylation.This research was partially supported by Grants from DGAPA (IN206302) and CONACyT (079908).

Regulation of Group II Metabotropic Glutamate Receptors by G Protein-Coupled Receptor Kinases: mGlu2 Receptors Are Resistant to Homologous Desensitization

We examined the regulation of mGlu2 and mGlu3 metabotropic glutamate receptor signaling prompted by the emerging role of these receptor subtypes as therapeutic targets for psychiatric disorders, such as anxiety and schizophrenia. In transfected human embryonic kidney 293 cells, G-protein-coupled receptor kinase (GRK) 2 and GRK3 fully desensitized the agonist-dependent inhibition of cAMP formation mediated by mGlu3 receptors. In contrast, GRK2 or other GRKs did not desensitize the cAMP response to mGlu2 receptor activation. Desensitization of mGlu3 receptors by GRK2 required an intact kinase activity, as shown by the use of the kinase-dead mutant GRK2-K220R or the recombinant GRK2 C-terminal domain. Overexpression of beta-arrestin1 also desensitized mGlu3 receptors and did not affect the cAMP signaling mediated by mGlu2 receptors. The difference in the regulation of mGlu2 and mGlu3 receptors was signal-dependent because GRK2 desensitized the activation of the mitogen-activated protein kinase pathway mediated by both mGlu2 and mGlu3 receptors. In vivo studies confirmed the resistance of mGlu2 receptor-mediated cAMP signaling to homologous desensitization. Wild-type, mGlu2(-/-), or mGlu3(-/-) mice were treated intraperitoneally with saline or the mixed mGlu2/3 receptor agonist (-)-2-oxa-4-aminobicyclo[3.1.0]-exhane-4,6-dicarboxylic acid (LY379268; 1 mg/kg) once daily for 7 days. Inhibition of forskolin-stimulated cAMP formation by LY379268 was measured in cortical slices prepared 24 h after the last injection. Agonist pretreatment fully desensitized the cAMP response in wild-type and mGlu2(-/-) mice but had no effect in mGlu3(-/-) mice, in which LY379268 could only activate the mGlu2 receptor. We predict the lack of tolerance when mixed mGlu2/3 receptor agonists or selective mGlu2 enhancers are used continually in patients.

Role of protein kinase C and mu-opioid receptor (MOPr) desensitization in tolerance to morphine in rat locus coeruleus neurons.

In morphine tolerance a key question that remains to be answered is whether μ-opioid receptor (MOPr) desensitization contributes to morphine tolerance, and if so by what cellular mechanisms. Here we demonstrate that MOPr desensitization can be observed in single rat brainstem locus coeruleus (LC) neurons following either prolonged (> 4 h) exposure to morphine in vitro or following treatment of animals with morphine in vivo for 3 days. Analysis of receptor function by an operational model indicated that with either treatment morphine could induce a profound degree (70–80%) of loss of receptor function. Ongoing PKC activity in the MOPr-expressing neurons themselves, primarily by PKCα, was required to maintain morphine-induced MOPr desensitization, because exposure to PKC inhibitors for only the last 30–50 min of exposure to morphine reduced the MOPr desensitization that was induced both in vitro and in vivo. The presence of morphine was also required for maintenance of desensitization, as washout of morphine for > 2 h reversed MOPr desensitization. MOPr desensitization was homologous, as there was no change in α2-adrenoceptor or ORL1 receptor function. These results demonstrate that prolonged morphine treatment induces extensive homologous desensitization of MOPrs in mature neurons, that this desensitization has a significant PKC-dependent component and that this desensitization underlies the maintenance of morphine tolerance.

The C-terminal Tail of CRTH2 Is a Key Molecular Determinant That Constrains Gαi and Downstream Signaling Cascade Activation

Prostaglandin D(2) activation of the seven-transmembrane receptor CRTH2 regulates numerous cell functions that are important in inflammatory diseases, such as asthma. Despite its disease implication, no studies to date aimed at identifying receptor domains governing signaling and surface expression of human CRTH2. We tested the hypothesis that CRTH2 may take advantage of its C-tail to silence its own signaling and that this mechanism may explain the poor functional responses observed with CRTH2 in heterologous expression systems. Although the C terminus is a critical determinant for retention of CRTH2 at the plasma membrane, the presence of this domain confers a signaling-compromised conformation onto the receptor. Indeed, a mutant receptor lacking the major portion of its C-terminal tail displays paradoxically enhanced Galpha(i) and ERK1/2 activation despite enhanced constitutive and agonist-mediated internalization. Enhanced activation of Galpha(i) proteins and downstream signaling cascades is probably due to the inability of the tail-truncated receptor to recruit beta-arrestin2 and undergo homologous desensitization. Unexpectedly, CRTH2 is not phosphorylated upon agonist-stimulation, a primary mechanism by which GPCR activity is regulated. Dynamic mass redistribution assays, which allow label-free monitoring of all major G protein pathways in real time, confirm that the C terminus inhibits Galpha(i) signaling of CRTH2 but does not encode G protein specificity determinants. We propose that intrinsic CRTH2 inhibition by its C terminus may represent a rather unappreciated strategy employed by a GPCR to specify the extent of G protein activation and that this mechanism may compensate for the absence of the classical phosphorylation-dependent signal attenuation.

Modeling the Role of Homologous Receptor Desensitization in Cell Gradient Sensing

G-protein-coupled chemoattractant receptors signal transiently upon ligand binding to effect cell orientation and motility but then are rapidly desensitized. The importance of desensitization has been unclear, because mutated nondesensitizable receptors mediate efficient chemotaxis. We hypothesized that homologous receptor desensitization is required for cellular navigation in fields of competing attractants. Modeling of receptor-mediated orientation shows that desensitization allows integration of attractant signals. Cells expressing normal receptors are predicted to 1) orient preferentially to distant gradients; 2) seek an intermediate position between balanced agonist sources; 3) and can be repositioned between chemoattractant-defined microenvironmental domains by modest changes in receptor number. In contrast, in the absence of desensitization, orientation is dominated by local agonist sources, precluding continued navigation. Furthermore, cell orientation in competing ligand gradients depends on the relative kinetic rates of receptor desensitization and recycling. We propose that homologous receptor desensitization is critical for cellular navigation in complex chemoattractant fields.

Dual Role of the β2-Adrenergic Receptor C Terminus for the Binding of β-Arrestin and Receptor Internalization

Homologous desensitization of beta2-adrenergic and other G-protein-coupled receptors is a two-step process. After phosphorylation of agonist-occupied receptors by G-protein-coupled receptor kinases, they bind beta-arrestins, which triggers desensitization and internalization of the receptors. Because it is not known which regions of the receptor are recognized by beta-arrestins, we have investigated beta-arrestin interaction and internalization of a set of mutants of the human beta2-adrenergic receptor. Mutation of the four serine/threonine residues between residues 355 and 364 led to the loss of agonist-induced receptor-beta-arrestin2 interaction as revealed by fluorescence resonance energy transfer (FRET), translocation of beta-arrestin2 to the plasma membrane, and receptor internalization. Mutation of all seven serine/threonine residues distal to residue 381 did not affect agonist-induced receptor internalization and beta-arrestin2 translocation. A beta2-adrenergic receptor truncated distal to residue 381 interacted normally with beta-arrestin2, whereas its ability to internalize in an agonist-dependent manner was compromised. A similar impairment of internalization was observed when only the last eight residues of the C terminus were deleted. Our experiments show that the C terminus distal to residue 381 does not affect the initial interaction between receptor and beta-arrestin, but its last eight amino acids facilitate receptor internalization in concert with beta-arrestin2.

HISTAMINE‐INDUCED PROGRESSION FROM HETEROLOGOUS TO HOMOLOGOUS DESENSITIZATION OF CONTRACTION IN SMOOTH MUSCLE OF GUINEA‐PIG TAENIA CAECI

1. We have reported previously that, in the smooth muscle of guinea-pig taenia caeci, the development of carbachol-induced desensitization to carbachol and histamine has a similar time-course whereas desensitization to high K(+) is interrupted by sustained resensitization. 2. In the present study, we evaluated the development of histamine-induced desensitization to histamine, carbachol and high K(+) with respect to their regulation by resensitization, and compared it with carbachol-induced desensitization. 3. Desensitization to histamine developed following pretreatment with 10(-5) mol/L histamine for 30 min with a tendency of transient interruption by resensitization at 1 min. In contrast, histamine-induced desensitization to carbachol and high K(+) was transient, peaking at around 15 s and 2 min, respectively, followed by sustained resensitization up to complete restoration within 2 and 10 min, respectively. 4. Thus, in contrast with carbachol, histamine initially induces heterologous desensitization, followed by sustained resensitization to carbachol and high K(+), resulting in selective and sustained homologous desensitization to histamine. 5. Thus, differences in the development of histamine- and carbachol-induced heterologous desensitization/resensitization contribute to the selective regulation of receptor-mediated signal transduction pathways.

Prostaglandin H2 induces the migration of human eosinophils through the chemoattractant receptor homologous molecule of Th2 cells, CRTH2

The major mast cell product PGD2 is released during the allergic response and stimulates the chemotaxis of eosinophils, basophils, and Th2-type T lymphocytes. The chemoattractant receptor homologous molecule of Th2 cells (CRTH2) has been shown to mediate the chemotactic effect of PGD2. PGH2 is the common precursor of all PGs and is produced by several cells that express cyclooxygenases. In this study, we show that PGH2 selectively stimulates human peripheral blood eosinophils and basophils but not neutrophils, and this effect is prevented by the CRTH2 receptor antagonist (+)-3-[[(4-fluorophenyl)sulfonyl] methyl amino]-1,2,3,4-tetrahydro-9H-carbazole-9-acetic acid (Cay10471) but not by the hematopoietic PGD synthase inhibitor 4-benzhydryloxy-1-[3-(1H-tetrazol-5-yl)-propyl]piperidine (HQL79). In chemotaxis assays, eosinophils showed a pronounced migratory response toward PGH2, but eosinophil degranulation was inhibited by PGH2. Moreover, collagen-induced platelet aggregation was inhibited by PGH2 in platelet-rich plasma, which was abrogated in the presence of the D-type prostanoid (DP) receptor antagonist 3-[(2-cyclohexyl-2-hydroxyethyl)amino]-2,5-dioxo-1-(phenylmethyl)-4-imidazolidine-heptanoic acid (BWA868c). Each of these effects of PGH2 was enhanced in the presence of plasma and/or albumin. In eosinophils, PGH2-induced calcium ion (Ca2+) flux was subject to homologous desensitization with PGD2. Human embryo kidney (HEK)293 cells transfected with human CRTH2 or DP likewise responded with Ca2+ flux, and untransfected HEK293 cells showed no response. These data indicate that PGH2 causes activation of the PGD2 receptors CRTH2 and DP via a dual mechanism: by interacting directly with the receptors and/or by giving rise to PGD2 after catalytic conversion by plasma proteins.

G Protein-Coupled Receptor-Receptor Tyrosine Kinase Receptor Crosstalk: Regulation of Receptor Sensitivity and Roles of Autocrine Feedback Loops and Signal Integration

Receptor tyrosine kinases (RTKs) can induce G protein-coupled receptor (GPCR) desensitization and phosphorylation. In some cases phosphorylation by RTKs on GPCRs tyrosine residues is involved, while in others indirect action through diverse protein kinases takes place. GPCRs stimulation can lead to RTK activation through the action of metalloproteinases, shedding of HB-EGF, and EGF receptor activation; such autocrine loop participates in the overall action triggered by GPCRs. Interestingly, it also has a role in GPCR phosphorylation and desensitization induced by activation of unrelated agents acting through their own GPCRs, and even in homologous desensitization. Phosphorylation and desensitization of some GPCRs by RTKs is pertussis toxin-sensitive, suggesting a role of G proteins. This might involve interaction between G proteins and RTKs but also of another autocrine loop, which includes sphingosine kinase I activation, sphingosine 1-phosphate generation and release and sphingosine 1-phosphate GPCR stimulation. RTKs can also use GPCRs as accessory signalling elements placing G proteins downstream of RTKs. In this signal integration mechanism, synthesis/ release of GPCR agonists is not essential. Crosstalk between GPCRs and RTKs has both basic and clinical implications, and has roles in physiologic and pathologic conditions offering multiple sites for therapeutic intervention.

Molecular analysis of the bovine anaphylatoxin C5a receptor

Recruitment of phagocytes to inflammatory sites involves the coordinated action of several chemoattractants, including the anaphylatoxin C5a. While the C5a receptor (C5aR) has been well characterized in humans and rodents, little is known about the bovine C5aR. Here, we report cloning of bovine C5R1, the gene encoding bovine C5aR. We also analyzed genomic sequence upstream of the C5R1 translation start site. Although the bovine C5aR amino acid sequence was well conserved among species, significant differences in conserved features were found, including major differences in the N terminus, intracellular loop 3, and transmembrane domain VII. Analysis of C5aR expression by flow cytometry and confocal microscopy demonstrated high levels of C5aR on all bovine neutrophils and a subset of bovine monocytes. C5aR was not expressed on resting or activated bovine lymphocytes, although C5aR message was present in these cells. C5aR was also expressed on a small subset of bovine mammary epithelial cells. Pharmacological analysis of bovine C5aR-mediated responses showed that bovine C5a and C5adesArg both induced dose-dependent calcium fluxes and chemotaxis in bovine neutrophils, with similar efficacy for both agonists. Treatment of bovine neutrophils with C5a or C5adesArg resulted in homologous desensitization of bovine C5aR and cross-desensitization to interleukin 8 (IL-8) and platelet-activating factor (PAF); whereas, treatment with IL-8 or PAF did not cross-desensitize the cells to C5a or C5adesArg. Overall, these studies provide important information regarding distinct structural and functional features that may contribute to the unique pharmacological properties of bovine C5aR.

Erratum: Ca2+ responses to thyrotropin‐releasing hormone and angiotensin II: the role of plasma membrane integrity and effect of G11α protein overexpression on homologous and heterologous desensitization

Erratum: Ca²⁺ responses to thyrotropin‐releasing hormone and angiotensin II: the role of plasma membrane integrity and effect of G₁₁<i>α</i> protein overexpression on homologous and heterologous desensitization

Increased RhoGDI2 and peroxiredoxin 5 levels in asthmatic murine model of β2-adrenoceptor desensitization: A proteomics approach

Beta(2)-adrenoceptor (beta(2)AR) desensitization is a common problem in clinical practice. beta(2)AR desensitization proceeds by at least such three mechanisms as heterologous desensitization, homologous desensitization and a kind of agonist-induced rapid phosphorylation by a variety of serine/threonine kinases. It is not clear whether there are other mechanisms. This study aimed to investigate potential mechanisms of beta(2)AR desensitization. Twenty-four BALB/c (6-8 weeks old) mice were divided into three groups, which is, group A, phosphate buffered saline (PBS)-treated; group B, ovalbumin (OVA)-induced; and group C, salbutamol-treated. Inflammatory cell counts, cytokine concentrations of bronchoalveolar lavage fluid (BALF), pathological sections, total serum IgE, airway responsiveness, membrane receptor numbers and total amount of beta(2)AR were observed. Asthmatic mouse model and beta(2)AR desensitization asthmatic mouse model were established. Groups B and C were selected for two-dimensional gel electrophoresis (2DE) analysis so as to find key protein spots related to beta(2)AR desensitization. Asthmatic mouse model and beta(2)AR desensitization asthmatic mouse model were verified by inflammatory cell count, cytokine concentration of BALF, serum IgE level, airway hyperreactivity measurement, radioligand receptor binding assay, Western blot analysis, and pathologic examination. Then the two groups (groups B and C) were subjected to 2DE. Two key protein spots associated with beta(2)AR desensitization, Rho GDP-dissociation inhibitor 2 (RhoGDI(2)) and peroxiredoxin 5, were found by comparative proteomics (2DE and mass spectrum analysis). Oxidative stress and small G protein regulators may play an important role in the process of beta(2)AR desensitization.

Prolonged 5-HT1A/5-HT2A receptor cross-talk is absent prior to adulthood in rats

In adult rats, serotonin 1A (5-HT1A) receptor activation produces heterologous desensitization of serotonin 2A (5-HT2A) neuroendocrine function at 1 h that persists up to 72 h. This study determined whether prolonged 5-HT1A/5-HT2A cross-talk exists before sexual maturation. Adolescent male rats (postnatal day 39) received an injection with saline or (+)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide [(+)8-OH-DPAT] 24 h before receiving a challenge injection of saline, (+)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide, or (-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl [(-)DOI] o assess changes in basal, 5-HT1A, and 5-HT2A receptor-mediated hormone responses. Although homologous desensitization of 5-HT1A neuroendocrine responses was present at 24 h, heterologous desensitization of 5-HT2A neuroendocrine responses was not. These data suggest that 5-HT1A heterologous desensitization of 5-HT2A receptor function does not develop until adulthood, is more transient, or follows a different time course before maturation.