Usnic acid (UA), a secondary lichen metabolite, has long been popular as one of natural fat-burning dietary supplements. Similar to 2,4-dinitrophenol, the weight-loss effect of UA is assumed to be associated with its protonophoric uncoupling activity. Recently, we have shown that the ability of UA to shuttle protons across both mitochondrial and artificial membranes is strongly modulated by the presence of calcium ions in the medium. Here, by using fluorescent probes, we studied the calcium-transporting capacity of usnic acid in a variety of membrane systems comprising liposomes, isolated rat liver mitochondria, erythrocytes and rat basophilic leukemia cell culture (RBL-2H3). At concentrations of tens of micromoles, UA appeared to be able to carry calcium ions across membranes in all the systems studied. Similar to the calcium ionophore A23187, UA caused degranulation of RBL-2H3 cells. Therefore, UA, being a protonophoric uncoupler of oxidative phosphorylation, at higher concentrations manifests itself as a calcium ionophore, which could be relevant to its overdose toxicity in humans and also its phytotoxicity.

中文翻译：

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松萝酸作为钙离子载体和肥大细胞的刺激剂。

松萝酸（UA）是一种次生的地衣代谢产物，长期以来一直作为天然脂肪燃烧膳食补充剂之一广受欢迎。与2,4-二硝基苯酚相似，UA的减肥作用被认为与其质子脱偶联活性有关。最近，我们已经表明，UA质子跨线粒体和人造膜穿梭的能力受到培养基中钙离子的强烈调节。在这里，我们通过使用荧光探针，研究了松香酸在包括脂质体，分离的大鼠肝线粒体，红细胞和大鼠嗜碱性白血病细胞培养物（RBL-2H3）在内的各种膜系统中的钙转运能力。在数十微摩尔的浓度下，UA在所有研究的系统中似乎都能将钙离子携带通过膜。与钙离子载体A23187类似，UA引起RBL-2H3细胞脱粒。因此，UA是高浓度的氧化磷酸化的质子脱偶联剂，其自身表现为钙离子载体，这可能与其在人体内的药物过量毒性以及植物毒性有关。