title: Adenosine A(2a) receptor-mediated inhibition of rod opsin mRNA expression in tiger salamander.
abstract: The neuromodulator adenosine mediates dark-adaptive changes in retinal photoreceptors through A(2a) receptors. In cold-blooded vertebrates, opsin mRNA expression is lower at night than during the day. In the present study, we tested whether adenosine could inhibit opsin mRNA expression in cultured rod cells and if endogenous adenosine acts to suppress opsin mRNA in the intact retina at night. Semi-quantitative in situ hybridization showed that treatment with 100 nm of the A(2a)/A(2b) agonist N(6)-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)-ethyl]adenosine (DPMA) reduced opsin mRNA 41% in cultured rod cells. The effect of DPMA was blocked by 10 microm of the A(2a) antagonist 8-(3-chlorostyryl)caffeine (CSC) but not by 10 microm of the A(2b) antagonist alloxazine. One micromolar adenosine alone had no effect on opsin mRNA. However, in the presence of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA), 1 microm adenosine reduced opsin mRNA 61%. EHNA alone reduced opsin mRNA by 26%. Consistent with an A(2a) receptor mechanism, 100 nm forskolin (adenylate cyclase agonist) decreased opsin mRNA 34%. Finally, northern blots showed that intravitreal injection of 10 microm CSC at night increased opsin I mRNA 38%. Thus, endogenous adenosine suppresses rod opsin I mRNA expression at night; in vitro results indicate this reduction occurs through A(2a)-like receptor binding and stimulation of adenylate cyclase activity.
authors.affiliation: Department of Neurosciences, UMDNJ-New Jersey Medical School, Newark, NJ, USA. alfinipe@umdnj.edu
authors.forename: Peter D
authors.initials: PD
authors.lastname: Alfinito
authors.forename: Roshni
authors.initials: R
authors.lastname: Alli
authors.forename: Ellen
authors.initials: E
authors.lastname: Townes-Anderson
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D058892:Adenosine Deaminase Inhibitors; D000262:Adenylyl Cyclases / Q000187:drug effects / Q000378:metabolism; D000557:Ambystoma; D000818:Animals; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D003624:Darkness; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D058906:Purinergic P1 Receptor Agonists; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017299:Rod Opsins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D058892:Adenosine Deaminase Inhibitors; D004791:Enzyme Inhibitors; D058906:Purinergic P1 Receptor Agonists; D012333:RNA, Messenger; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1; D017299:Rod Opsins; C056426:CGS 24012; D005576:Colforsin; C010192:9-(2-hydroxy-3-nonyl)adenine; D000262:Adenylyl Cyclases; D000225:Adenine; D000241:Adenosine