Kusama Nobuyoshi, Kajikuri Junko, Yamamoto Tamao, Watanabe Yoshimasa, Suzuki Yoshikatsu, Katsuya Hirotada, Itoh Takeo
Department of Cellular and Molecular Pharmacology, Graduate School of Medical Sciences, Nagoya City University, Kawasumi 1, Nagoya, Aichi 467-8601, Japan.
Br J Pharmacol. 2005 Oct;146(4):487-97. doi: 10.1038/sj.bjp.0706363.
This study was undertaken to determine whether long-term in vivo administration of nitroglycerine (NTG) downregulates the hyperpolarization induced by acetylcholine (ACh) in aortic valve endothelial cells (AVECs) of the rabbit and, if so, whether antioxidant agents can normalize this downregulated hyperpolarization. ACh (0.03-3 microM) induced a hyperpolarization through activations of both apamin- and charybdotoxin-sensitive Ca2+-activated K+ channels (K(Ca)) in rabbit AVECs. The intermediate-conductance K(Ca) channel (IK(Ca)) activator 1-ethyl-2-benzimidazolinone (1-EBIO, 0.3 mM) induced a hyperpolarization of the same magnitude as ACh (3 microM). The ACh-induced hyperpolarization was significantly weaker, although the ACh-induced [Ca2+]i increase was unchanged, in NTG-treated rabbits (versus NTG-untreated control rabbits). The hyperpolarization induced by 1-EBIO was also weaker in NTG-treated rabbits. The reduced ACh-induced hyperpolarization seen in NTG-treated rabbits was not modified by in vitro application of the superoxide scavengers Mn-TBAP, tiron or ascorbate, but it was normalized when ascorbate was coadministered with NTG in vivo. Superoxide production within the endothelial cell (estimated by ethidium fluorescence) was increased in NTG-treated rabbits and this increased production was normalized by in vivo coadministration of ascorbate with the NTG. It is suggested that long-term in vivo administration of NTG downregulates the ACh-induced hyperpolarization in rabbit AVECs, possibly through chronic actions mediated by superoxide.
本研究旨在确定长期体内给予硝酸甘油（NTG）是否会下调兔主动脉瓣内皮细胞（AVECs）中乙酰胆碱（ACh）诱导的超极化，如果是，抗氧化剂是否能使这种下调的超极化恢复正常。ACh（0.03 - 3 microM）通过激活兔AVECs中对蜂毒明肽和美洲箭毒素敏感的钙激活钾通道（K（Ca））诱导超极化。中间电导K（Ca）通道（IK（Ca））激活剂1 - 乙基 - 2 - 苯并咪唑啉酮（1 - EBIO，0.3 mM）诱导的超极化幅度与ACh（3 microM）相同。在NTG处理的兔中，尽管ACh诱导的细胞内钙浓度（[Ca2 +]i）增加未改变，但ACh诱导的超极化明显减弱（与未处理的NTG对照兔相比）。在NTG处理的兔中，1 - EBIO诱导的超极化也较弱。在NTG处理的兔中观察到的ACh诱导的超极化减弱，在体外应用超氧化物清除剂锰 - 四（4 - 苯甲酸）卟啉（Mn - TBAP）、钛铁试剂或抗坏血酸时未得到改善，但当抗坏血酸与NTG在体内共同给药时，这种超极化恢复正常。在NTG处理的兔中，内皮细胞内的超氧化物产生（通过乙锭荧光估计）增加，而在体内将抗坏血酸与NTG共同给药可使这种增加的产生恢复正常。提示长期体内给予NTG可能通过超氧化物介导的慢性作用下调兔AVECs中ACh诱导的超极化。
