Uc Aliye, Reszka Krzysztof J, Buettner Garry R, Stokes John B
The University of Iowa, Carver College of Medicine, Iowa City, IA 52242, USA.
Am J Physiol Cell Physiol. 2007 May;292(5):C1906-14. doi: 10.1152/ajpcell.00550.2006. Epub 2007 Jan 10.
Heme induces Cl(-) secretion in intestinal epithelial cells, most likely via carbon monoxide (CO) generation. The major source of endogenous CO comes from the degradation of heme via heme oxygenase (HO). We hypothesized that an inhibitor of HO activity, tin protoporphyrin (SnPP), may inhibit the stimulatory effect of heme on Cl(-) secretion. To test this hypothesis, we treated an intestinal epithelial cell line (Caco-2 cells) with SnPP. In contrast to our expectations, Caco-2 cells treated with SnPP had an increase in their short-circuit currents (I(sc)) in Ussing chambers. This effect was observed only when the system was exposed to ambient light. SnPP-induced I(sc) was caused by Cl(-) secretion because it was inhibited in Cl(-)-free medium, with ouabain or 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). The Cl(-) secretion was not via activation of the CFTR, because a specific inhibitor had no effect. Likewise, inhibitors of adenylate cyclase and guanylate cyclase had no effect on the enhanced I(sc). SnPP-induced I(sc) was inhibited by the antioxidant vitamins, alpha-tocopherol and ascorbic acid. Electron paramagnetic resonance experiments confirmed that oxidative reactions were initiated with light in cells loaded with SnPP. These data suggest that SnPP-induced effects may not be entirely due to the inhibition of HO activity but rather to light-induced oxidative processes. These novel effects of SnPP-photosensitized oxidation may also lead to a new understanding of how intestinal Cl(-) secretion can be regulated by the redox environment of the cell.
血红素可诱导肠上皮细胞分泌氯离子，最有可能是通过生成一氧化碳（CO）来实现的。内源性CO的主要来源是血红素经血红素加氧酶（HO）降解产生。我们推测，HO活性抑制剂锡原卟啉（SnPP）可能会抑制血红素对氯离子分泌的刺激作用。为验证这一假设，我们用SnPP处理了一种肠上皮细胞系（Caco-2细胞）。与我们的预期相反，用SnPP处理的Caco-2细胞在尤斯灌流小室中的短路电流（I(sc)）增加。只有当系统暴露于环境光时才会观察到这种效应。SnPP诱导的I(sc)是由氯离子分泌引起的，因为在无氯培养基中，用哇巴因或5-硝基-2-(3-苯丙基氨基)苯甲酸（NPPB）处理可抑制该效应。氯离子分泌并非通过激活囊性纤维化跨膜传导调节因子（CFTR），因为一种特异性抑制剂对此没有作用。同样，腺苷酸环化酶和鸟苷酸环化酶的抑制剂对增强的I(sc)也没有作用。SnPP诱导的I(sc)可被抗氧化维生素α-生育酚和抗坏血酸抑制。电子顺磁共振实验证实，在加载SnPP的细胞中，光照会引发氧化反应。这些数据表明，SnPP诱导的效应可能并非完全归因于HO活性的抑制，而是光诱导的氧化过程。SnPP光敏氧化的这些新效应也可能会使人们对细胞氧化还原环境如何调节肠道氯离子分泌有新的认识。
