title: Bitter tastants induce relaxation of rat thoracic aorta precontracted with high K(+).
abstract: It has been reported that bitter tastants decrease blood pressure and relax precontracted vascular smooth muscle. However, the underlying mechanisms remain unclear. The aim of the present study was to determine the mechanism underlying the vasorelaxant effect of the bitter tastants. Thoracic aortic rings were isolated from Wistar rats and contractions were measured using an isometric myograph. Intracellular Ca(2+) ([Ca(2+)]i) in single rat thoracic aortic smooth muscle cells was recorded by calcium imaging. Calcium currents in single cells were recorded using patch-clamp techniques. High K(+) (140 mmol/L) induced contractions in rat thoracic aortic rings that were inhibited by 3 mmol/L chloroquine, 3 mmol/L denatonium and 10 μmol/L nifedipine. In single rat thoracic aortic smooth muscle cells, high K(+) increased [Ca(2+)]i and this effect was also blocked by 3 mmol/L chloroquine and 10 μmol/L nifedipine. Under Ca(2+) -free conditions, high K(+) failed to induce contractions in rat thoracic aortic rings. On its own, chloroquine had no effect on the muscle tension of rat aortic rings and [Ca(2+) ]i. The vasorelaxant effects of chloroquine on precontracted rat thoracic aortic rings were not altered by either 1 μg/mL pertussis toxin (PTX), an inhibitor of Gαo/i-protein, or 1 mmol/L gallein, an inhibitor of Gβγ-protein. The results of patch-clamp analysis in single cells indicate that 1 mmol/L chloroquine blocks voltage-dependent L-type Ca(2+) channel (VDLCC) currents from both extracellular and intracellular sides. Together, the results indicate that chloroquine can block VDLCC, independent of PTX- and gallein-sensitive G-proteins, resulting in relaxation of high K(+)-precontracted thoracic aortic smooth muscle.
authors.affiliation: Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China, College of Life Sciences, South-Central University for Nationalities, Wuhan, China.
authors.forename: Wen-Bo
authors.initials: WB
authors.lastname: Sai
authors.forename: Meng-Fei
authors.initials: MF
authors.lastname: Yu
authors.forename: Ming-Yu
authors.initials: MY
authors.lastname: Wei
authors.forename: Zhongju
authors.initials: Z
authors.lastname: Lu
authors.forename: Yun-Min
authors.initials: YM
authors.lastname: Zheng
authors.forename: Yong-Xiao
authors.initials: YX
authors.lastname: Wang
authors.forename: Gangjian
authors.initials: G
authors.lastname: Qin
authors.forename: Donglin
authors.initials: D
authors.lastname: Guo
authors.forename: Guangju
authors.initials: G
authors.lastname: Ji
authors.forename: Jinhua
authors.initials: J
authors.lastname: Shen
authors.forename: Qing-Hua
authors.initials: QH
authors.lastname: Liu
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology; D002118:Calcium; D002738:Chloroquine / Q000494:pharmacology; D005421:Flavoring Agents / Q000494:pharmacology*; D037342:Pertussis Toxin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D014661:Vasoconstriction / Q000187:drug effects*; D014966:Xanthenes / Q000494:pharmacology
chemical_list: D005421:Flavoring Agents; D014966:Xanthenes; D002738:Chloroquine; C007820:gallein; D037342:Pertussis Toxin; D011188:Potassium; D002118:Calcium
keywords: L-type Ca2+ channels; bitter tastants; chloroquine; intracellular Ca2+; patch clamp; relaxation