title: Desensitization of adenosine A(1) receptors in rat immature cortical neurons.
abstract: Adenosine plays an important neuroprotective role in brain, usually mediated by the activation of adenosine A₁ receptors. Prolonged activation of a G-protein-coupled receptor generally leads to the partial loss of the responsiveness of receptor-mediated transduction pathways (desensitization). Rat immature cortical neurons were treated with 100 nM⁻N⁶-phenylisopropyladenosine (R-PIA), a selective A₁ receptor agonist, and the effect on adenosine A₁ receptor/adenylyl cyclase pathway was studied. Incubation with R-PIA for 6, 12, 24 and 48 h elicited a time-dependent decrease in adenosine A₁ receptors in plasma membranes (92, 58, 43 and 26% of control, respectively), which was associated with variations in microsomal fraction (21, 56, 124 and 233% of control, respectively), suggesting the internalization and down-regulation of adenosine A₁ receptors. Moreover, real-time PCR assays showed a significant increase in mRNA levels coding adenosine A₁ receptor after the longest treatment period (48 h). In addition, αGi₁₋₂ protein levels detected in microsomes and mRNA levels coding αGi₁ protein were increased after 48 h of treatment with R-PIA, suggesting the synthesis of new αGi₁ proteins. Finally, adenylyl cyclase inhibition elicited by 2-Chloro-N6-cyclopentyladenosine (CPA), a selective adenosine A₁ receptor agonist, was significantly reduced after 12, 24 and 48h of treatment (37, 24 and 23%, respectively) as compared to controls (54%), suggesting the desensitization of adenosine A₁ receptor/adenylyl cyclase pathway. These results suggest that adenosine A₁ receptors desensitize slowly after prolonged receptor activation in immature cortical neurons, showing mechanisms of desensitization similar to those described not only in fetal but also in adult rat brain.
authors.affiliation: Departamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de Ciencias Químicas, Centro Regional de Investigaciones Biomédicas, Universidad de Castilla-La Mancha, Ciudad Real, Spain
authors.forename: María Ángeles
authors.initials: MÁ
authors.lastname: Ruiz
authors.forename: David Agustín
authors.initials: DA
authors.lastname: León
authors.forename: José Luis
authors.initials: JL
authors.lastname: Albasanz
authors.forename: Mairena
authors.initials: M
authors.lastname: Martín
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D058907:Adenosine A1 Receptor Agonists / Q000494:pharmacology*; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000096:biosynthesis; D005786:Gene Expression Regulation / Q000187:drug effects; D009474:Neurons / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D043682:Receptor, Adenosine A1 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
chemical_list: D058907:Adenosine A1 Receptor Agonists; D043682:Receptor, Adenosine A1; C047235:N-(1-methyl-2-phenylethyl)adenosine; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases; D000241:Adenosine