Cyclopentyladenosine-induced homologous down-regulation of A1 adenosine receptors (A1AR) in intact neurons is accompanied by receptor sequestration but not a reduction in A1AR mRNA expression or G protein alpha-subunit content.
We showed previously that exposure of cerebellar granule cells to the A1 adenosine receptor (A1AR)-selective agonist, cyclopentyladenosine, decreases A1AR density and G protein coupling corresponding to blunted agonist-induced adenylyl cyclase (EC 4.6.1.1) inhibition. We have now determined that A1AR-mediated adenylyl cyclase inhibition was desensitized in a homologous manner. Carbachol- and baclofen-induced inhibition of adenylyl cyclase was unaffected by 48-h exposure to 10 microM cyclopentyladenosine. Expression of G protein alpha-subunits was not affected dramatically by agonist exposure. The fraction of sequestered A1AR was increased significantly at 4, 24, and 48 h of cyclopentyladenosine exposure (35, 57, and 81% increase over control, respectively). The time course of agonist-induced A1AR sequestration was slower than that reported for other G protein-coupled receptors. Incubation with the adenosine receptor antagonist, 8-p-sulfophenyltheophylline or adenosine deaminase did not alter sequestration significantly. Neither steady-state A1AR mRNA levels nor transcript stability was affected by 48-h agonist exposure. We determined that A1AR half-life in cerebellar granule cells is 20.9 h, which is considerably longer than that reported for several other G protein-coupled receptors. The slow time course of A1AR sequestration and the stability of the corresponding mRNA may be a reflection of the tonic inhibitory tone exerted by adenosine in brain.
Hettinger
B D
BD
College of Pharmacy, Oregon State University, Corvallis, USA.
Leid
M
M
Murray
T F
TF
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D015536:Down-Regulation / Q000187:drug effects; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D009474:Neurons / Q000737:chemistry* / Q000187:drug effects / Q000201:enzymology; D058906:Purinergic P1 Receptor Agonists; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018047:Receptors, Purinergic P1 / Q000235:genetics* / Q000378:metabolism*; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D014316:Tritium; D014970:Xanthines / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D058906:Purinergic P1 Receptor Agonists; D012333:RNA, Messenger; D018047:Receptors, Purinergic P1; D014970:Xanthines; D014316:Tritium; C048599:N(6)-cyclopentyladenosine; C031433:8-(4-sulfophenyl)theophylline; C051360:1,3-dipropyl-8-cyclopentylxanthine; D013806:Theophylline; D019205:GTP-Binding Protein alpha Subunits, Gs; D000262:Adenylyl Cyclases; D000241:Adenosine