title: Is dopamine-induced inhibition of adenylate cyclase involved in the autoreceptor-mediated negative control of tyrosine hydroxylase in striatal dopaminergic terminals?
abstract: The mechanism of the negative control of tyrosine hydroxylase (TH) activity induced by the stimulation of presynaptic 3,4-dihydroxyphenylethylamine (dopamine, DA) autoreceptors was investigated using rat striatal slices and synaptosomes incubated under control ([ K+] = 4.8 mM) or depolarizing ([ K+] = 60 mM) conditions. The stimulation of DA autoreceptors by 7-hydroxy-2-(di-n-propylamino)tetralin (1 microM 7-OH-DPAT) produced a significant decrease in TH activity extracted from striatal slices maintained under control conditions. This effect was associated with the complete conversion of TH into an enzyme form with a low affinity for its pterin cofactor (Km approximately 0.80 mM). Furthermore, compared to TH extracted from control tissues, that from 7-OH-DPAT-exposed striatal slices was more sensitive to the stimulatory effects of exogenous heparin and cyclic AMP-dependent phosphorylation. Such changes were opposite to those induced by incubating striatal slices with the adenylate cyclase activator forskolin. Indeed, forskolin treatment completely converted TH into an enzyme form with a high affinity for its pterin cofactor (Km approximately 0.16 mM). Such conversion was associated with a shift in the optimal pH for TH activity from 5.8 (control) to 7.2 (forskolin). Under depolarizing conditions, the blockade by (-)-sulpiride of the stimulation of DA autoreceptors by endogenous DA was associated with a marked activation of TH. Modifications of enzymatic characteristics triggered by (-)-sulpiride were then similar to those induced by forskolin treatment. These data suggest that presynaptic DA autoreceptors modulate the activity of TH by controlling the degree of cyclic AMP-dependent phosphorylation of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D003342:Corpus Striatum / Q000201:enzymology*; D000242:Cyclic AMP / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology*; D006493:Heparin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000378:metabolism*; D013469:Sulpiride / Q000494:pharmacology; D013574:Synaptosomes / Q000201:enzymology; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D001552:Benzazepines; D011954:Receptors, Dopamine; D013764:Tetrahydronaphthalenes; D010566:Virulence Factors, Bordetella; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D013469:Sulpiride; D006493:Heparin; D000242:Cyclic AMP; D014446:Tyrosine 3-Monooxygenase; D000262:Adenylyl Cyclases; D004298:Dopamine