Kitazawa T, Takaoka K, Taneike T
Department of Pharmacology, Faculty of Veterinary Medicine, Rakuno Gakuen University, Hokkaido, Japan.
J Auton Pharmacol. 1999 Apr;19(2):65-75. doi: 10.1046/j.1365-2680.1999.00117.x.
The present experiments were designed to clarify the mechanisms of the inhibitory response of 5-hydroxytryptamine (5-HT) in the porcine uterine circular muscle. Inhibitory responses induced by 5-HT (1 nM-1 microM) were not affected by apamin (1 microM), charybdotoxin (100 nM) or glibenclamide (20 microM) but were significantly attenuated by 4-aminopyridine (3 mM) and tetraethylammonium (3 mM). Imidazole (100 microM) decreased but 3-isobutyl-1-methylxanthine (30 microM), milrinone (30 microM) and Ro 20-1724 (10 and 30 microM) potentiated the 5-HT-induced inhibition. On the other hand, zaprinast (3-30 microM) had no significant effect on the inhibitory response of 5-HT. 5-HT caused a time (0-5 min)-and concentration (1 nM-1 microM)-dependent increase in the tissue cyclic AMP level, but had no effect on the tissue cyclic GMP level. A significant correlation (P < 0.05) was observed between the inhibition of contraction and tissue cyclic AMP level. The effect of 5-HT on contractile force and cytosolic Ca2+ level ([Ca2+]i) was investigated using fura-PE3-loaded myometrial strips. A low concentration of 5-HT (< or = 10 nM) inhibited the spontaneous contraction without changing the amplitude of the spontaneous [Ca2+]i increase, but a higher concentration of 5-HT (> or = 100 nM) decreased the resting [Ca2+]i and inhibited both the spontaneous [Ca2+]i increase and spontaneous contraction. High-K+ (50 mM) caused increases in muscle contractile force and [Ca2+]i. 5-HT concentrationdependently inhibited the high-K(+)-induced contraction (EC50, 45 nM) with only a small decrease in [Ca2+]i increase. Carbachol also caused increases in muscle contractile force and [Ca2+]i. 5-HT significantly decreased both the carbachol-induced contraction and [Ca2+]i increase, but was more potent at inhibition of contractile force than [Ca2+]i. In Ca(2+)-loaded myometrial strips, carbachol, but not caffeine, caused a transient increase in [Ca2+]i and contraction in the absence of external Ca2+ (EGTA, 1 mM). 5-HT inhibited both the carbachol-induced increases in [Ca2+]i release and contractile force. In the beta-escin permeabilized myometrium, 5-HT significantly inhibited the Ca(2+)-induced contraction. The present results indicate that 5-HT stimulates tissue cyclic AMP production, and inhibits the porcine uterine muscle contractility by a reduction in [Ca2+]i and in Ca2+ sensitivity of the contractile elements. Activation of K+ channels might be partially involved in 5-HT-induced inhibition of the myometrial contractility.
本实验旨在阐明5-羟色胺（5-HT）对猪子宫环行肌的抑制反应机制。5-HT（1 nM - 1 microM）诱导的抑制反应不受蜂毒明肽（1 microM）、蝎毒素（100 nM）或格列本脲（20 microM）影响，但4-氨基吡啶（3 mM）和四乙铵（3 mM）可使其显著减弱。咪唑（100 microM）可使其降低，但3-异丁基-1-甲基黄嘌呤（30 microM）、米力农（30 microM）和Ro 20-1724（10和30 microM）可增强5-HT诱导的抑制作用。另一方面，扎普司特（3 - 30 microM）对5-HT的抑制反应无显著影响。5-HT可引起组织环磷酸腺苷（cAMP）水平随时间（0 - 5分钟）和浓度（1 nM - 1 microM）依赖性升高，但对组织环磷酸鸟苷（cGMP）水平无影响。收缩抑制与组织cAMP水平之间存在显著相关性（P < 0.05）。使用fura-PE3标记的子宫肌条研究了5-HT对收缩力和胞质钙离子水平（[Ca2+]i）的影响。低浓度的5-HT（≤10 nM）可抑制自发收缩，而不改变自发[Ca2+]i升高的幅度，但高浓度的5-HT（≥100 nM）可降低静息[Ca2+]i，并抑制自发[Ca2+]i升高和自发收缩。高钾（50 mM）可引起肌肉收缩力和[Ca2+]i升高。5-HT浓度依赖性地抑制高钾诱导的收缩（半数有效浓度，45 nM），而[Ca2+]i升高仅有小幅降低。卡巴胆碱也可引起肌肉收缩力和[Ca2+]i升高。5-HT可显著降低卡巴胆碱诱导的收缩和[Ca2+]i升高，但对收缩力的抑制作用比对[Ca2+]i的抑制作用更强。在钙离子负载的子宫肌条中，卡巴胆碱而非咖啡因可在无细胞外钙离子（乙二醇双四乙酸，1 mM）的情况下引起[Ca2+]i短暂升高和收缩。5-HT可抑制卡巴胆碱诱导的[Ca2+]i释放增加和收缩力。在β-七叶皂苷通透的子宫肌层中，5-HT可显著抑制钙离子诱导的收缩。目前的结果表明，5-HT刺激组织cAMP生成，并通过降低[Ca2+]i和收缩元件对钙离子的敏感性来抑制猪子宫肌收缩力。钾通道的激活可能部分参与了5-HT诱导的子宫肌收缩力抑制。
