Biomedical subjects

Christophe Blanchet

Publications and source records attributed to Christophe Blanchet.

3 recordsLinked to original sources

PubMed2003

Integrated databanks access and sequence/structure analysis services at the PBIL.

The World Wide Web server of the PBIL (Pôle Bioinformatique Lyonnais) provides on-line access to sequence databanks and to many tools of nucleic acid and protein sequence analyses. This server allows to query nucleotide sequence banks in the EMBL and GenBank formats and protein sequence banks in the SWISS-PROT and PIR formats. The query engine on which our data bank access is based is the ACNUC system. It allows the possibility to build complex queries to access functional zones of biological interest and to retrieve large sequence sets. Of special interest are the unique features provided by this system to query the data banks of gene families developed at the PBIL. The server also provides access to a wide range of sequence analysis methods: similarity search programs, multiple alignments, protein structure prediction and multivariate statistics. An originality of this server is the integration of these two aspects: sequence retrieval and sequence analysis. Indeed, thanks to the introduction of re-usable lists, it is possible to perform treatments on large sets of data. The PBIL server can be reached at: http://pbil.univ-lyon1.fr.

Databases, Genetic↗

PubMed2003

Two distinct forms of desensitization of G-protein coupled inwardly rectifying potassium currents evoked by alkaloid and peptide mu-opioid receptor agonists.

Mu-opioid receptors (MORs) activate G-protein coupled inwardly rectifying potassium (GIRK) channels. The peptide agonist [D-Ala(2), NMe-Phe(4), Gly(5)-ol]enkephalin (DAMGO), but not the alkaloid morphine (MS), leads to acute desensitization of this response. Furthermore, DAMGO, as opposed to MS, triggers rapid internalization of MORs. Given this dichotomy, we probed the relationship between receptor internalization and GIRK current desensitization in neurons of the locus coeruleus (LC) using acute rat brain slices. Interfering with MOR recycling by selective impairment of dynamin-dependent endocytosis left GIRK current desensitization unchanged. Conversely, coapplication of MS with a low concentration of DAMGO, a cocktail reported to enhance MOR internalization, revealed competition between the two agonists and normal desensitization. We also examined the case of methadone (MD), an alkaloid that has been reported to strongly trigger endocytosis. Interestingly, MD and other alkaloids agonists did induce GIRK current desensitization, but only at suprasaturating concentrations. Furthermore, responses to alkaloids were blunted in LC neurons and the same agonists inhibited GIRK currents in cells that do not express MORs. Our results indicate that two distinct forms of MOR-evoked GIRK current desensitization exist. Peptide agonists induce receptor-mediated desensitization while alkaloid agonists lead to apparent desensitization by receptor-independent inhibition of GIRK channels.

Alkaloids↗

PubMed2002

Desensitization of mu-opioid receptor-evoked potassium currents: initiation at the receptor, expression at the effector.

Many G protein-coupled receptor-mediated responses desensitize within minutes. Sustained stimulation of mu-opioid receptors (MORs), which primarily signal through G(i/o) proteins, leads to activation and subsequent desensitization of G protein-coupled inwardly rectifying potassium (GIRK) currents. We observed that in neurons of the locus coeruleus, which express among the highest levels of MORs in the brain, the degree of desensitization depended on the intensity of receptor stimulation, indicating that the process is initiated at the receptor. Interestingly, while GIRK-mediated postsynaptic inhibition substantially desensitized within 15 min, presynaptic inhibition of afferent transmission, which involves other effector systems, remained constant, suggesting that the postsynaptic desensitization we observed is expressed at the effector. We show that desensitized GIRK currents can gradually be reactivated by additional G protein signals of increasing intensity and present evidence that desensitization is a G protein-mediated process. Finally, desensitization of MOR-induced GIRK currents had heterologous effects on responses mediated by other G protein-coupled receptors converging onto the same population of GIRK channels. Taken together, our results provide evidence for a form of desensitization mediated by a slowly developing G protein-dependent pathway, initiated at the MORs and leading to competitive inhibition of GIRK channel activation. This implies that MORs exert a bidirectional action on GIRK channels.

Animals↗