Reversible and non-competitive antagonist profile of CPCCOEt at the human type 1 alpha metabotropic glutamate receptor

In transfected CHO cells expressing the human metabotropic glutamate receptor mGlu1 alpha, 7- hydroxyimino)cyclopropan[b]chromen-1a-carboxylic acid ethylester (CPCCOEt) was found to antagonize L-quisqualate-induced phosphoinositide hydrolysis in a non-competitive and reversible manner (apparent pK(i) value, 4.76 +/- 0.18: It = 3. This suggests that CPCCOEt antagonizes type Ir metabotropic glutamate receptor activation by interacting with a site distinct from the agonist binding site. (C) 1998 Elsevier Science Ltd. All rights reserved

Binding and activity of the nine possible regioisomers of myo-inositol tetrakisphosphate at the inositol 1,4,5-trisphosphate receptor

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Complex involvement of pertussis toxin-sensitive G proteins in the regulation of type 1 alpha metabotropic glutamate receptor signaling in baby hamster kidney cells

Previously, we demonstrated that the coupling of the metabotropic glutamate receptor mGlu1 alpha to phosphoinositide hydrolysis is enhanced by pertussis toxin (PTX) in stably transfected baby hamster kidney cells (BHK). Here, we show that the PTX effect on agonist-stimulated [H-3]inositol phosphate accumulation can be resolved into two components: an immediate increase in agonist potency, and a more slowly developing increase in the magnitude of the response observed at maximally effective agonist concentrations. Using G(q)/(11)alpha- and G(i/o)alpha-selective antibodies to immunoprecipitate [S-35]guanosine-5'-O-(3-thio)triphosphate-bound G alpha proteins, we also show that agonist stimulation of mGlu1a in BHK membranes increases specific [S-35]guanosine-5'-O-(3-thio)triphosphate binding to both G(q/11) and G(i/o) proteins. Preincubation of BHK-mGlu1 alpha with L-glutamate (300 mu M) results in a progressive loss (60% in 30 min) of L-quisqualate-induced [H-3]inositol phosphate accumulation (without a change in potency), providing evidence for agonist-induced receptor desensitization. Although such desensitization of mGlu receptor signaling was mimicked by a phorbol ester, agonist-induced phosphorylation of the receptor was not observed and protein kinase C inhibition by Ro 31-8220 did not prevent L-glutamate-mediated desensitization. In contrast, PTX treatment of the cells almost completely prevented L-glutamate-mediated desensitization. Together, these data provide evidence for a multifunctional coupling of mGlu1a to different types of G proteins, including PTX-sensitive G(i)-type G proteins. The latter are involved in the negative control of phospholipase C activity while also influencing the rate of desensitization of the mGlu1 alpha receptor

Compliance for uncertain inventories via probabilistic/fuzzy comparison of alternatives

A direct comparison among highly uncertain inventories of emissions is inadequate and may lead to paradoxes. This issue is of particular importance in the case of greenhouse gases. This paper reviews the methods for the comparison of uncertain inventories in the context of compliance checking. The problem is treated as a comparison of uncertain alternatives. It provides a categorization and ranking of the inventories which can induce compliance checking conditions. Two groups of techniques to compare uncertain estimates are considered in the paper: probabilistic and fuzzy approaches. They show certain similarities which are revealed and stressed throughout the paper. The group of methods most suitable for the compliance purpose is distinguished. They introduce new conditions for fulfilling compliance, depending on inventory uncertainty. These new conditions considerably change the present approach, where only the reported values of inventories are accounted for

Inhibition of N-linked glycosylation of the human type 1 alpha metabotropic glutamate receptor by tunicamycin: effects on cell-surface receptor expression and function

The potential role of N-linked glycosylation of the human type 1 alpha metabotropic glutamate (mGlu1 alpha) receptor was studied in a recombinant, inducible expression system, where receptor expression was induced in the absence and presence of tunicamycin. In the absence of tunicamycin the mGlu1 alpha receptor appeared to be expressed, at least in part, as a dimer consisting of monomers of approx. 145 and 160 KDa relative molecular mass (M-r). In the presence of tunicamycin only a single monomeric protein could be detected approximating the M-r predicted for the human mGlu1 alpha receptor based on its primary amino acid sequence (130 KDa). Exposure to tunicamycin during receptor induction did not appear to affect the cell surface expression of the mGlu1 alpha receptor as determined immunocytochemically or using a cell-surface biotinylation strategy, but reduced agonist-stimulated phosphoinositide hydrolysis by approximately 50% compared to control cell populations. Our data suggest that non-N-glycosylated human mGlu1 alpha receptors can traffic to the cell surface and activate phospholipase C. (C) 1999 Elsevier Science Ltd. All rights reserved