title: Stimulation of dopamine synthesis and activation of tyrosine hydroxylase by phorbol diesters in rat striatum.
abstract: In rat striatal synaptosomes, 4 beta-phorbol 12-myristate 13-acetate (PMA) and 4 beta-phorbol 12,13-dibutyrate (PDBu), two activators of Ca2+-phospholipid-dependent protein kinase (protein kinase C) increased dopamine (DA) synthesis measured by following the release of 14CO2 from L-[1-14C] tyrosine. Maximal stimulation (21-28% increase of basal rate) was produced by 0.5 microM PMA and 1 microM PDBu. 4 beta-Phorbol and 4 beta-phorbol 13-acetate, which are not activators of protein kinase C, were ineffective at 1 microM. PMA did not change the release of 14CO2 from L-[1-14C]DOPA. Addition of 1 mM EGTA to a Ca2+-free incubation medium failed to affect PMA stimulation. KC1 (60 mM) enhanced DA synthesis by 25%. Exposure of synaptosomes to either PMA or PDBu prior to KC1 addition resulted in a more than additive increase (80-100%) of DA synthesis. A similar synergistic effect was observed when the phorbol diesters were combined with either veratridine or d-amphetamine but not with forskolin and dibutyryl cyclic AMP. Pretreatment of striatal synaptosomes with phorbol diesters produced an activation on of tyrosine hydroxylase (TH) associated with a 60% increase of the Vmax and a decrease of the Km for the pterine cofactor 6-methyl-5,6,7,8-tetrahydropterin. These results indicate that protein kinase C participates in the regulation of striatal TH in situ and that its activation may act synergistically with DA releasing agents in stimulating DA synthesis.
mesh_terms: D000818:Animals; D003342:Corpus Striatum / Q000201:enzymology*; D004298:Dopamine / Q000096:biosynthesis*; D004789:Enzyme Activation / Q000187:drug effects; D008297:Male; D010703:Phorbol Esters / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000201:enzymology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
chemical_list: D010703:Phorbol Esters; D011189:Potassium Chloride; D014701:Veratridine; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine