Seabra V, Stachlewitz R F, Thurman R G
Department of Pharmacology, University of North Carolina at Chapel Hill, 27599-7365, USA.
J Leukoc Biol. 1998 Nov;64(5):615-21. doi: 10.1002/jlb.64.5.615.
Activation of Kupffer cells by lipopolysaccharide (LPS) plays a pivotal role in the onset of pathophysiological events that occur during endotoxemia and intracellular calcium ([Ca2+]i) is involved in LPS-stimulated cytokine production. Recently, it was shown that Kupffer cells contain a glycine-gated chloride channel. Because taurine, a ubiquitous sulfur-containing beta-amino acid, acts similarly to glycine in neurons by causing hyperpolarization, it was hypothesized that taurine would act via a similar mechanism, blunting the LPS-induced increase in [Ca2+]i in Kupffer cells. To test this hypothesis, Kupffer cells were isolated from female Sprague-Dawley rats and cultured for 24 h. LPS-induced changes in [Ca2+]i were monitored fluorometrically in single cells, whereas levels of tumor necrosis factor alpha (TNF-alpha) released by Kupffer cells after exposure to LPS were measured by enzyme-linked immunosorbent assay. Taurine significantly blunted the LPS-induced increase in [Ca2+]i in a dose-dependent manner (IC50, 0.1 mM). This effect was reversed by strychnine (1 microM) and was prevented when chloride was removed from the extracellular media. Moreover, taurine increased 36Cl- uptake by Kupffer cells in a dose-dependent manner (EC50, 0.2 mM). Furthermore, strychnine (1 microM) reversed the effect of taurine on 36Cl- uptake. These results indicate that taurine activates a glycine-gated chloride channel in Kupffer cells causing chloride influx. In addition, LPS-induced TNF-alpha production was reduced by more than 40% by taurine, an effect that was also reversed by strychnine. In conclusion, taurine blocks the increase in [Ca2+]i due to LPS and significantly reduces TNF-alpha production by mechanisms involving chloride influx into the Kupffer cell.
脂多糖（LPS）激活库普弗细胞在内毒素血症期间发生的病理生理事件的起始中起关键作用，并且细胞内钙（[Ca2+]i）参与LPS刺激的细胞因子产生。最近，研究表明库普弗细胞含有甘氨酸门控氯离子通道。由于牛磺酸是一种普遍存在的含硫β-氨基酸，在神经元中通过引起超极化发挥与甘氨酸类似的作用，因此推测牛磺酸会通过类似机制发挥作用，减弱LPS诱导的库普弗细胞中[Ca2+]i的增加。为了验证这一假设，从雌性Sprague-Dawley大鼠中分离出库普弗细胞并培养24小时。通过荧光法监测单细胞中LPS诱导的[Ca2+]i变化，而通过酶联免疫吸附测定法测量库普弗细胞在暴露于LPS后释放的肿瘤坏死因子α（TNF-α）水平。牛磺酸以剂量依赖性方式显著减弱LPS诱导的[Ca2+]i增加（IC50，0.1 mM）。士的宁（1 microM）可逆转此效应，并且当从细胞外培养基中去除氯离子时该效应被阻止。此外，牛磺酸以剂量依赖性方式增加库普弗细胞对36Cl-的摄取（EC50，0.2 mM）。此外，士的宁（1 microM）逆转了牛磺酸对36Cl-摄取的作用。这些结果表明牛磺酸激活库普弗细胞中的甘氨酸门控氯离子通道，导致氯离子内流。此外，牛磺酸使LPS诱导的TNF-α产生减少超过40%，该效应也被士的宁逆转。总之，牛磺酸通过涉及氯离子流入库普弗细胞的机制阻断LPS引起的[Ca2+]i增加，并显著降低TNF-α产生。
