Parlani M, Manzini S, Argentino-Storino A, Conte B
Department of Pharmacology, Menarini Ricerche Sud, Pomezia, Roma, Italy.
J Pharmacol Toxicol Methods. 1992 Sep;28(2):85-90. doi: 10.1016/1056-8719(92)90052-3.
Electrical field stimulation (EFS, 2.5 Hz, 60 V, 1 ms, trains of 5 sec every 5 min) of the rat external urethral sphincter (EUS) produced contractile responses characterized by a "slow" tonic contraction on which was superimposed a series of phasic "twitch-like" contractions. Both responses were abolished by tetrodotoxin (0.6 microM), and their amplitude was significantly lower in samples taken from denervated (15 days before) sphincters. The tonic contraction showed duration, voltage, and frequency dependency, whereas the twitches were markedly duration dependent. No correlation was found between the amplitude of the tonic and that of the twitch-like contractions. Phentolamine (3 microM) reduced by 95% the amplitude of the tonic contraction produced by maximal parameters, whereas it did not affect the twitches. On the other hand, hexamethonium (10 microM) was ineffective on both components. Dantrolene (10 microM) inhibited the twitch response, whereas it did not influence the tonic component. Preincubation with d-tubocurarine (0.2 mM) or succinylcholine (2 mM) significantly inhibited the amplitude of twitches produced by EFS (0.1 Hz, 60 V) up to a duration of 50 microseconds. Stimulus width higher than 50 microseconds, resulted in twitches that were resistant to neuromuscular blocking agents but sensitive to dantrolene (10 microM). Our results indicate that the rat external urethral sphincter is a reliable and easy "in vitro" model for studying the activity of drugs capable of interfering with the nerve-mediated activity of the striated and smooth muscle portion of the urinary bladder outlet.
对大鼠尿道外括约肌（EUS）进行电场刺激（EFS，2.5赫兹，60伏，1毫秒，每5分钟施加5秒的刺激串）可产生收缩反应，其特征为“缓慢”的强直性收缩，并叠加有一系列阶段性的“抽搐样”收缩。两种反应均被河豚毒素（0.6微摩尔）消除，并且在取自去神经支配（15天前）括约肌的样本中，它们的幅度明显较低。强直性收缩表现出持续时间、电压和频率依赖性，而抽搐则明显依赖于持续时间。未发现强直性收缩幅度与抽搐样收缩幅度之间存在相关性。酚妥拉明（3微摩尔）可使最大参数产生的强直性收缩幅度降低95%，而对抽搐无影响。另一方面，六甲铵（10微摩尔）对这两种成分均无效。丹曲林（10微摩尔）抑制抽搐反应，而对强直性成分无影响。用d - 筒箭毒碱（0.2毫摩尔）或琥珀酰胆碱（2毫摩尔）预孵育可显著抑制EFS（0.1赫兹，60伏）产生的抽搐幅度，持续时间可达50微秒。刺激宽度高于50微秒时，产生的抽搐对神经肌肉阻滞剂有抗性，但对丹曲林（10微摩尔）敏感。我们的结果表明，大鼠尿道外括约肌是一种可靠且易于操作的“体外”模型，可用于研究能够干扰膀胱出口横纹肌和平滑肌部分神经介导活动的药物活性。
