title: Lack of cholinergic modulation of tyrosine hydroxylase activation by potassium.
abstract: Cholinergic modulation on the regulation of tyrosine hydroxylase was studied in guinea pig atria depolarized with high potassium concentration. In these conditions there was an increment in tyrosine hydroxylase activity as well as in the release of radioactivity from atria preincubated with 3H-noradrenaline. Both effects were concentration-dependent. Incubation in the presence of 10 microM methacholine, 31 microM 1,1 dimethyl-4-phenylpiperazinium iodide (DMPP), 0.15 microM atropine or 83 microM hexamethonium did not affect tyrosine hydroxylase activation by 100 mM K+. The percentage of activation was reduced however, when 7 microM physostigmine (acetylcholinesterase inhibitor) was present during depolarization. This effect is unlikely to be related to the increase of acetylcholine concentration in the interface, but more probably to a direct effect on the enzyme. In conclusion, tyrosine hydroxylase activation induced by 100 mM potassium appears to be unrelated to the stimulation of nicotinic and muscarinic presynaptic receptors.
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004789:Enzyme Activation; D005260:Female; D006168:Guinea Pigs; D006325:Heart Atria / Q000187:drug effects; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D008297:Male; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D010830:Physostigmine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D011621:Pteridines / Q000494:pharmacology; D011950:Receptors, Cholinergic / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D006584:Hexamethonium Compounds; D008688:Methacholine Compounds; D011621:Pteridines; D011950:Receptors, Cholinergic; D016210:Methacholine Chloride; D018738:Hexamethonium; D004246:Dimethylphenylpiperazinium Iodide; C005063:2-amino-4-hydroxy-6,7-dimethyl-5,6,7,8-tetrahydropteridine; D001285:Atropine; D010830:Physostigmine; D014446:Tyrosine 3-Monooxygenase; D011188:Potassium