title: Adenosine A(1) receptor-mediated inhibition of protein kinase A-induced calcitonin gene-related peptide release from rat trigeminal neurons.
abstract: Calcitonin gene-related peptide (CGRP), a potent vasodilator, has been implicated in the pathogenesis of migraine. Its release from adult rat trigeminal neurons in culture was shown to be markedly increased by the activation of adenylate cyclase with forskolin. Modulation of this secretion was investigated by a number of agents with known inhibitory effects on cAMP generation mediated via receptor coupling to G(i/o) proteins. Significantly, forskolin-stimulated CGRP release could be closely correlated with the phosphorylation of the protein kinase A (PKA) substrate cyclic AMP response element-binding protein (CREB). Forskolin-stimulated CGRP release could be potently and effectively inhibited by the adenosine A(1) receptor-selective agonist GR79236X (pIC(50) = 7.7 +/- 0.1, maximal inhibition 65 +/- 2.5% at 300 nM), whereas the A(2A) (CGS21680) and the A(3) (2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide) receptor-selective agonists were without effect. GR79236X-mediated inhibition was abolished by the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. Immunocytochemical studies and Western analysis revealed the presence of adenosine A(1) receptors on trigeminal neurons. However, despite the additional detection of 5-hydroxytryptamine (5-HT)(1B) receptors on these cells, the clinically effective antimigraine 5-HT(1B/1D) agonist sumatriptan did not inhibit forskolin-stimulated CGRP release nor did it show any effect on the concomitant CREB phosphorylation. In contrast, the mu-opioid agonist fentanyl elicited a 74 +/- 4% reduction in CGRP levels. Forskolin-stimulated CGRP release and CREB phosphorylation could be mimicked by incubation of the cells with chlorophenylthio-cAMP and blocked by pretreatment with the PKA inhibitor myrPKI(14-22). Taken together, the present data confirm the PKA-dependence of forskolin-stimulated CGRP release and suggest that A(1) adenosine agonists may warrant further investigation in models of migraine and neurogenic inflammation.
authors.affiliation: Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, Tennis Court Rd., Cambridge, CB2 1QJ, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Carruthers
authors.forename: L A
authors.initials: LA
authors.lastname: Sellers
authors.forename: D W
authors.initials: DW
authors.lastname: Jenkins
authors.forename: E M
authors.initials: EM
authors.lastname: Jarvie
authors.forename: W
authors.initials: W
authors.lastname: Feniuk
authors.forename: P P
authors.initials: PP
authors.lastname: Humphrey
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004347:Drug Interactions; D005283:Fentanyl / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010627:Phenethylamines / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D058906:Purinergic P1 Receptor Agonists; D051381:Rats; D017208:Rats, Wistar; D044302:Receptor, Serotonin, 5-HT1B; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000096:biosynthesis; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D018170:Sumatriptan / Q000494:pharmacology; D013572:Synaptic Vesicles / Q000201:enzymology / Q000378:metabolism; D014276:Trigeminal Nerve / Q000166:cytology / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D017362:Cyclic AMP Response Element-Binding Protein; D010627:Phenethylamines; D058906:Purinergic P1 Receptor Agonists; D044302:Receptor, Serotonin, 5-HT1B; D018047:Receptors, Purinergic P1; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D005576:Colforsin; D018170:Sumatriptan; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D015740:Calcitonin Gene-Related Peptide; D000241:Adenosine; C082299:N-((1S,trans)-2-hydroxycyclopentyl)adenosine; D005283:Fentanyl; C090034:2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methyluronamide