Adenosine A2a receptor‐mediated inhibition of rod opsin mRNA expression in tiger salamander

• Published in: Journal of neurochemistry 2002-11, Vol.83 (3), p.665-672
• Main Authors: Alfinito, Peter D., Alli, Roshni, Townes‐Anderson, Ellen
• Format: Article
• Language: English
• Subjects: A2a receptor; adenosine; Biological and medical sciences; Cell physiology; Fundamental and applied biological sciences. Psychology; Molecular and cellular biology; mRNA expression; opsin; retina; rod photoreceptor; Vision, photoreception
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.2002.01162.x

The neuromodulator adenosine mediates dark‐adaptive changes in retinal photoreceptors through A2a 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 A2a/A2b 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 µm of the A2a antagonist 8‐(3‐chlorostyryl)caffeine (CSC) but not by 10 µm of the A2b 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 µm adenosine reduced opsin mRNA 61%. EHNA alone reduced opsin mRNA by 26%. Consistent with an A2a receptor mechanism, 100 nm forskolin (adenylate cyclase agonist) decreased opsin mRNA 34%. Finally, northern blots showed that intravitreal injection of 10 µm 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 A2a‐like receptor binding and stimulation of adenylate cyclase activity.