Gu Xiang Q, Pamenter Matthew E, Siemen Detlef, Sun Xiaolu, Haddad Gabriel G
Section of Respiratory Medicine, Department of Pediatrics, University of California San Diego, La Jolla, California.
Glia. 2014 Apr;62(4):504-13. doi: 10.1002/glia.22620. Epub 2014 Jan 20.
Tumor cells are resistant to hypoxia but the underlying mechanism(s) of this tolerance remain poorly understood. In healthy brain cells, plasmalemmal Ca(2+)-activated K(+) channels ((plasma)BK) function as oxygen sensors and close under hypoxic conditions. Similarly, BK channels in the mitochondrial inner membrane ((mito)BK) are also hypoxia sensitive and regulate reactive oxygen species production and also permeability transition pore formation. Both channel populations are therefore well situated to mediate cellular responses to hypoxia. In tumors, BK channel expression increases with malignancy, suggesting these channels contribute to tumor growth; therefore, we hypothesized that the sensitivity of (plasma)BK and/or (mito)BK to hypoxia differs between glioma and healthy brain cells. To test this, we examined the electrophysiological properties of (plasma)BK and (mito)BK from a human glioma cell line during normoxia and hypoxia. We observed single channel activities in whole cells and isolated mitoplasts with slope conductance of 199 ± 8 and 278 ± 10 pA, respectively. These currents were Ca(2+)- and voltage-dependent, and were inhibited by the BK channel antagonist charybdotoxin (0.1 μM). (plasma)BK could only be activated at membrane potentials >+40 mV and had a low open probability (NPo) that was unchanged by hypoxia. Conversely, (mito)BK were active across a range of membrane potentials (-40 to +40 mV) and their NPo increased during hypoxia. Activating (plasma)BK, but not (mito)BK induced cell death and this effect was enhanced during hypoxia. We conclude that unlike in healthy brain cells, glioma (mito)BK channels, but not (plasma)BK channels are oxygen sensitive.
肿瘤细胞对缺氧具有抗性，但其耐受的潜在机制仍知之甚少。在健康脑细胞中，质膜钙激活钾通道（(plasma)BK）作为氧传感器，在缺氧条件下会关闭。同样，线粒体内膜中的BK通道（(mito)BK）也对缺氧敏感，可调节活性氧的产生以及通透性转换孔的形成。因此，这两种通道群体都处于良好位置，可介导细胞对缺氧的反应。在肿瘤中，BK通道的表达随恶性程度增加而升高，表明这些通道有助于肿瘤生长；因此，我们推测(plasma)BK和/或(mito)BK对缺氧的敏感性在胶质瘤细胞和健康脑细胞之间存在差异。为了验证这一点，我们检测了人胶质瘤细胞系中的(plasma)BK和(mito)BK在常氧和缺氧条件下的电生理特性。我们在全细胞和分离的线粒体中观察到单通道活性，其斜率电导分别为199±8和278±10 pA。这些电流依赖于钙和电压，并被BK通道拮抗剂蝎毒素（0.1μM）抑制。(plasma)BK仅在膜电位>+40 mV时被激活，且开放概率较低（NPo），缺氧时该概率不变。相反，(mito)BK在一系列膜电位（-40至+40 mV）下均有活性，且其NPo在缺氧时增加。激活(plasma)BK而非(mito)BK会诱导细胞死亡，且这种效应在缺氧时增强。我们得出结论，与健康脑细胞不同，胶质瘤中的(mito)BK通道而非(plasma)BK通道对氧敏感。
