Activation of adenosine A1 receptor by N6-(R)-phenylisopropyladenosine (R-PIA) inhibits forskolin-stimulated tyrosine hydroxylase activity in rat striatal synaptosomes.
We investigated the effect of the relatively selective A1 adenosine receptor agonist N6-(R)-phenylisopropyladenosine (R-PIA) on tyrosine hydroxylase activity (TH) of synaptosomes obtained from rat striatum. TH activity was assayed in supernatant obtained following sonication and centrifugation of the tissue preincubated with the test compounds. R-PIA produced a modest decrease of basal enzyme activity, but significantly reduced the activation of the enzyme by submaximal (0.1-0.5 microM) concentrations of forskolin (FSK) a stimulator of adenylate cyclase. The IC 50 value of R-PIA was 17 nM and the maximal inhibition corresponded to 30-40% decrease of the enzyme activity stimulated by FSK. The S-isomer of PIA failed to affect TH activity under control and stimulated conditions. Moreover, the inhibitory effect of R-PIA was completely antagonized by 8-cyclopentyl- 1,3 -dimethylxanthine, an adenosine receptor blocker. R-PIA inhibited both basal and FSK-stimulated adenylate cyclase activity. These results indicate that in striatal dopaminergic terminals TH activity can be modulated in an inhibitory manner by activation of presynaptic A1 adenosine receptors.
Olianas
M C
MC
Department of Neurosciences, University of Cagliari, Italy.
Onali
P
P
D000241:Adenosine / Q000031:analogs & derivatives*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D010660:Phenylisopropyladenosine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011983:Receptors, Purinergic / Q000187:drug effects* / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000201:enzymology; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors*
D011983:Receptors, Purinergic; D005576:Colforsin; D010660:Phenylisopropyladenosine; D014446:Tyrosine 3-Monooxygenase; D000241:Adenosine