Journal of Neuroscience, Vol 7, 2522-2528, Copyright © 1987 by Society for Neuroscience
Adenosine A1 receptor-mediated inhibition of adenylate cyclase in rabbit retina
C Blazynski
The purine adenosine has been postulated as playing a role in CNS
neurotransmission or modulation. Evidence is now provided that inhibition
of adenylate cyclase in rabbit retinal homogenates is mediated via
adenosine A1 receptors. Nanomolar concentrations of the A1 receptor
agonists, cyclohexyladenosine (CHA) and phenylisopropyladenosine (PIA),
significantly inhibited the activity of forskolin-stimulated adenylate
cyclase in preparations in which endogenous adenosine was destroyed by
pretreatment with adenosine deaminase. With increasing concentrations of
either agonist, biphasic effects on enzyme activity were observed. The
effect of the mixed A1-A2 agonist, N-ethyl-carboxamidoadenosine (NECA), on
forskolin-stimulated, as well as basal adenylate cyclase, was also
investigated. At micromolar concentrations, NECA significantly increased
the activity of adenylate cyclase. Isobutylmethylxanthine, a potent
antagonist at extracellular adenosine receptors, blocked the effects
observed with PIA, CHA, and NECA. The uptake of both 3H-CHA and
3H-adenosine into retinal cells was demonstrated autoradiographically. Both
agonists labeled ganglion cell bodies and certain cell bodies located in
the proximal portion of the inner nuclear layer.