title: Flavonoid galetin 3,6-dimethyl ether attenuates guinea pig ileum contraction through K(+) channel activation and decrease in cytosolic calcium concentration.
abstract: Flavonoid galetin 3,6-dimethyl ether (FGAL) has been isolated from the aerial parts of Piptadenia stipulaceae and has shown a spasmolytic effect in guinea pig ileum. Thus, we aimed to characterize its relaxant mechanism of action. FGAL exhibited a higher relaxant effect on ileum pre-contracted by histamine (EC50=1.9±0.4×10(-7) M) than by KCl (EC50=2.6±0.5×10(-6) M) or carbachol (EC50=1.8±0.4×10(-6) M). The flavonoid inhibited the cumulative contractions to histamine, as well as to CaCl2 in depolarizing medium nominally Ca(2+)-free. The flavonoid relaxed the ileum pre-contracted by S-(-)-Bay K8644 (EC50=9.5±1.9×10(-6) M) but less potently pre-contracted by KCl or histamine. CsCl attenuated the relaxant effect of FGAL (EC50=1.1±0.3×10(-6) M), but apamin or tetraethylammonium (1mM) had no effect (EC50=2.6±0.2×10(-7) and 1.6±0.3×10(-7) M, respectively), ruling out the involvement of small and big conductance Ca(2+)-activated K(+) channels (SKCa and BKCa, respectively). Either 4-aminopyridine or glibenclamide attenuated the relaxant effect of FGAL (EC50=1.8±0.2×10(-6) and 1.5±0.5×10(-6) M, respectively), indicating the involvement of voltage- and ATP-sensitive K(+) channels (KV and KATP, respectively). FGAL did not alter the viability of intestinal myocytes in the MTT assay and decreased (88%) Fluo-4 fluorescence, indicating a decrease in cytosolic Ca(2+) concentration. Therefore, the relaxant mechanism of FGAL involves pseudo-irreversible noncompetitive antagonism of histaminergic receptors, KV and KATP activation and blockade of CaV1, thus leading to a reduction in cytosolic Ca(2+) levels.
authors.affiliation: Programa de Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Universidade Federal da Paraíba, Campus I, 58051-970 João Pessoa, Paraíba, Brazil.
authors.forename: Luiz H C
authors.initials: LH
authors.lastname: Vasconcelos
authors.affiliation: Programa de Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Universidade Federal da Paraíba, Campus I, 58051-970 João Pessoa, Paraíba, Brazil.
authors.forename: Ana C de C
authors.initials: AC
authors.lastname: Correia
authors.affiliation: Programa de Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Universidade Federal da Paraíba, Campus I, 58051-970 João Pessoa, Paraíba, Brazil.
authors.forename: Iara L L
authors.initials: IL
authors.lastname: de Souza
authors.affiliation: Programa de Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Universidade Federal da Paraíba, Campus I, 58051-970 João Pessoa, Paraíba, Brazil.
authors.forename: Maria da C C
authors.initials: Mda C
authors.lastname: Silva
authors.affiliation: Departamento de Biofísca, Universidade Federal de São Paulo, 04021-001 São Paulo, São Paulo, Brazil.
authors.forename: Edgar J
authors.initials: EJ
authors.lastname: Paredes-Gamero
authors.affiliation: Programa de Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Universidade Federal da Paraíba, Campus I, 58051-970 João Pessoa, Paraíba, Brazil; Departamento de Ciências Farmacêuticas, Universidade Federal da Paraíba, Campus I, 58051-900 João Pessoa, Paraíba, Brazil.
authors.forename: Bárbara V de O
authors.initials: BV
authors.lastname: Santos
authors.affiliation: Programa de Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Universidade Federal da Paraíba, Campus I, 58051-970 João Pessoa, Paraíba, Brazil; Departamento de Fisiologia e Patologia, Universidade Federal da Paraíba, Campus I, 58051-900 João Pessoa, Paraíba, Brazil. Electronic address: fabianacavalcante@ltf.ufpb.br.
authors.forename: Fabiana de A
authors.initials: Fde A
authors.lastname: Cavalcante
authors.affiliation: Programa de Pós-graduação em Produtos Naturais e Sintéticos Bioativos, Universidade Federal da Paraíba, Campus I, 58051-970 João Pessoa, Paraíba, Brazil; Departamento de Ciências Farmacêuticas, Universidade Federal da Paraíba, Campus I, 58051-900 João Pessoa, Paraíba, Brazil.
authors.forename: Bagnólia A
authors.initials: BA
authors.lastname: da Silva
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D005419:Flavonoids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D006633:Histamine Antagonists / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects* / Q000502:physiology; D032342:Muscle Cells / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000819:agonists*; D011189:Potassium Chloride / Q000037:antagonists & inhibitors / Q000494:pharmacology; D019789:Tetraethylammonium
chemical_list: D002712:Chlorides; D005419:Flavonoids; D006633:Histamine Antagonists; D026902:Potassium Channel Blockers; D015221:Potassium Channels; C570563:galetin 3,6-dimethyl ether; D002586:Cesium; D001030:Apamin; D019789:Tetraethylammonium; D011189:Potassium Chloride; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D006632:Histamine; D002217:Carbachol; D015761:4-Aminopyridine; C028019:cesium chloride; D002122:Calcium Chloride; D005905:Glyburide; D002118:Calcium
keywords: Calcium; Flavonoid; Galetin 3,6-dimethyl ether; Galetin-3,6-dimethyl ether (PubChem CID: 5352032); Ileum; Potassium channels; S-(−)-Bay K8644 (PubChem CID: 2303); and 4-aminopyridine (PubChem 4-AP) (CID: 1727).; apamin (PubChem CID: 16218850); calcium chloride (PubChem CID: 6093260); carbachol (PubChem CID: 5831); cesium chloride (PubChem CID: 24293); glibenclamide (PubChem CID: 3488); histamine (PubChem CID: 774); potassium chloride (PubChem CID: 4873); tetraethylammonium chloride (CID: 5413); verapamil (PubChem CID: 62969)