摘要:

AbstractCGP 12177A originally was developed as a hydrophilic antagonist to detect cell surfaceβ1- andβ2-adrenergic receptors, and sub-sequently was found to be a partial agonist for the atypical orβ3-adrenergic receptor. Using hamster cells stably expressing either the humanβ1-, humanβ2- or ratβ1-adrenergic receptor, we found that CGP 12177A behaved as an agonist forβ1-adrenergic receptors. Whereas at low concentrations, CGP 12177A behaved as an antagonist and inhibited isoproterenol stimulation of adenylyl cyclase activity, at higher concentrations, it stimulated a response even in the absence of isoproterenol. The agonistic properties of CGP 12177A were positively correlated with the level ofβ1-adrenergic receptor expression. Thus, at low receptor densities, CGP 12177A behaved as a weak, partial agonist whereas as high receptor densities, the drug was a full agonist. At similar high densities of theβ2-adrenergic receptor, CGP 12177A acted only as a partial agonist. Competition binding studies to membranes from cells expressingβ1-adrenergic receptors indicated that -90% of the receptors were in a high affinity, guanine nucleotide-insensitive state for CGP 12177A whereas -10% of the receptors were in a lower affinity, guanine nucleotide-sensitive state for CGP 12177A. We propose that the latter receptors are precoupled to stimulatory G proteins and recognize CGP 12177A as an agonist whereas the high affinity, uncoupled receptors recognize CGP 12177A as an antagonist.

ISSN:1079-9893    

DOI:10.3109/10799899609039938

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe in vitro contractile effect of neuropeptide Y (NPY) on rat myometrial strips was for the first time demonstrated and characterised, and the EC50value estimated to be 267±87 nM. This effect is presumably mediated by the NPY1receptor being responsible for postsynaptic effects throughout the peripherial nervous system, thus indicating a direct uterotonic effect of NPY. Further, the effect was demonstrated to be dependent on extracellular Ca2+. Short-term exposures to NPY markedly desensitized the tissue affecting subsequent responses to NPY as well as to oxytocin (OT). This desensitization was time-and concentration-dependent, but lasted less than three hours. However, long-term infusions of NPY for 5 days increased the response to both NPY and OT. Long-term infusions of OT caused a marked decrease of the NPY response, and it is concluded that common pathways for up and down regulation of the myometrial responsiveness to several peptide hormones may exist.

ISSN:1079-9893    

DOI:10.3109/10799899609039939

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractGTP is one of the major cellular molecules involved in fundamental functions of cell life. Ribavirin, an antiviral and antitumoral agent, the primary site of action of which is the IMP deshydrogenase, was used in order to depress the intracellular GTP level. Consequential effects were tested on the property and dynamic of the VIP receptor on human melanoma IGR 39 cells. A concentration of 100μM of Ribavirin reduced the intracellular GTP level by more than 60% and induced a reversible growth arrest. Nevertheless this drug displayed no effect on: i) the VIP binding parameters (Kdand Bmax) of both high and low affinity receptors; ii) the cycling of the VIP receptor; iii) the basal and VIP-stimulated cAMP production and iv) the subcellular GTP distribution. We show that Ribavirin, in the range of concentrations used, is very efficient to inhibit GTP synthesis in the human melanoma cell line IGR 39 and its growth, without affecting VIP receptor functions.

ISSN:1079-9893    

DOI:10.3109/10799899609039940

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe formyl peptide receptor on human neutrophils recognizes bacterial, N-formylated peptides and initiates a cascade of intracellular signals via a pertussis toxin sensitive G1protein. We used fluorescence techniques to investigate the interactions of ligand (L), receptor (R), and G proteins (G), the ternary complex, in both live and fixed human neutrophils. By lightly fixing permeabilized neutrophils with a procedure that retained ligand binding, we were able to“capture”R and G in different configurations in the absence of ligand. Fixed receptors were trapped in a high affinity form (attributed to LRG) that could not be rapidly converted to low affinity by the addition of GTP[S]. Adding saturating nucleotide prior to fixation trapped receptors in a low affinity form (attributed to LR). The low affinity receptors retained the sensitivity of the native receptors to the presence of Na+. The distribution between high and low affinity receptors was modulated by GTP[S] in a dose dependent manner. The ability to redistribute low and high affinity receptor forms prior to fixation was unique to GTP[S], as compared to other non-activating nucleotides, suggesting that GTP[S] can regulate the distribution between R and RG. We suggest that precoupled receptors that give rise to high affinity ligand binding are likely to exist in native membranes in human neutrophils.

ISSN:1079-9893    

DOI:10.3109/10799899609039941

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWe have synthesized a series of peptides corresponding to portions of the extracellular domain of human granulocyte-macrophage colony stimulating factor receptorαsubunit (hGM-CSFRα). The sequences were chosen according to the homology between hGM-CSFRαand the growth hormone receptor (GHR) and correspond to the regions reported to form the binding site of the latter receptor. The peptides were examined for their binding activity to hGM-CSF by affinity chromatography on resin-immobilized hGM-CSF and by a solid phase binding assay. Four peptides endowed with hGM-CSF binding activity were identified and the postulated homology between the binding sites of hGM-CSFRαand GHR was confirmed.

ISSN:1079-9893    

DOI:10.3109/10799899609039942

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe binding and distribution of radiolabelled SR27897B, a potent CCK-A antagonist, was characterized using in vitro receptor autoradiography. Rapid imaging and quantitative analysis of [3H]SR27897B binding was obtained in a very short period of time (5 days) with a highly sensitive radioimager ensuring very short exposure times for isotopes such as tritium. Tritiated SR27897B binding sites are localized almost exclusively in the area postrema and the medial part of the nucleus tractus solitarius and in this nucleus the rostral-caudal distribution of CCK-A sites differed from that of sulphated CCK8 receptors. Receptor binding properties analyzed on 15μm serial coronal sections showed one site receptor occupancy in these two regions with high affinity and selectivity characteristic of the CCK-A receptor. These results precisely locate the SR27897B binding sites and provide further support for the absence of heterogeneity of the CCK-A receptors in the rat brain.

ISSN:1079-9893    

DOI:10.3109/10799899609039943

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractWe have identified one class of IGF-I-binding sites and two classes of IGF-II-binding sites at the surface of the melanoma cell line IGR39. By means of affinity labeling with125I-IGF-I, a 290–300 kDa form was characterized. Using125I-IGF-II, a 270 kDa polypeptide was labeled, corresponding to the type II IGF receptor. In the two serials of experiments, the order of potency in inhibiting 125I-IGF-I or125I-IGF-II labeling of IGF-related peptides andαIR3, an antibody directed against type I receptorαsubunit, was the same as in competition experiments. When IGR39 cells were cultured in a serum-free medium, the number of both high affinity IGF-II and IGF-I binding sites was increased, by 8-and 5-fold respectively, without any significant change in Kdvalues. In both culture conditions, we found IGFBP-2, -3, -4 and a 30 kDa form which Mr was consistent with IGFBP-5 or -6. Except for IGFBP-2, the amount of secreted IGFBPs was modified depending on culture conditions: in conditioned medium from cells cultured with 10% FCS, the amount of IGFBP-3 or -4 was higher, and the amount of the 30 kDa IGFBP was lower when compared to conditioned medium from cells cultured in serum-free medium.

ISSN:1079-9893    

DOI:10.3109/10799899609039944

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractIn this study we looked for evidence regarding a correlation between M2-muscarinic receptor binding affinity and ligand intrinsic activity. Guanine nucleotide-binding protein-coupled receptors have been shown to exist in both a high affinity and a low affinity, agonist state. The agonist [3H]Oxotremorine-M, was used to determine the affinity of compounds for the high affinity state and the antagonist, [3H]N-methylscopolamine, plus GppNHp, was used to determine the affinity for the low agonist state. The magnitude of the difference in the affinity a compound has for the high versus the low agonist state of the receptor has been related to the intrinsic activity of the compound. NMS/Oxo-M ratios were established for muscarinic agonists, partial agonists and antagonists. NMS/Oxo-M ratios varied from 1695 for the agonist carbachol to 1.9 for the antagonist AFDX-116 with intermediate values for the partial agonists oxotremorine-M, pilocarpine and RS86 (233, 36 and 17 respectively). Intrinsic activity was assessed by receptor-mediated Gi-protein GTPase activity. Indeed, a close correlation (r=0.92) was found between the NMS/Oxo-M ratios of the ligands on the one hand, and their ability to activate the M2-receptor coupled Gi-protein on the other.

ISSN:1079-9893    

DOI:10.3109/10799899609039945

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor