Department of Physiology, University of Tübingen, Gmelinstr. 5, D-72076 Tübingen, Germany.
FASEB J. 2012 Oct;26(10):4243-53. doi: 10.1096/fj.12-208132. Epub 2012 Jul 5.
The energy-sensing AMP-activated serine/threonine protein kinase (AMPK) confers cell survival in part by stimulation of cellular energy production and limitation of cellular energy utilization. AMPK-sensitive functions further include activities of epithelial Na+ channel ENaC and voltage-gated K+ channel KCNE1/KCNQ1. AMPK is activated by an increased cytosolic Ca2+ concentration. The present study explored whether AMPK regulates the Ca2+-sensitive large conductance and voltage-gated potassium (BK) channel. cRNA encoding BK channel was injected into Xenopus oocytes with and without additional injection of wild-type AMPK (AMPKα1+AMPKβ1+AMPKγ1), constitutively active AMPKγR70Q, or inactive AMPKαK45R. BK-channel activity was determined utilizing the 2-electrode voltage-clamp. Moreover, BK-channel protein abundance in the cell membrane was determined by confocal immunomicroscopy. As BK channels are expressed in outer hair cells (OHC) of the inner ear and lack of BK channels increases noise vulnerability, OHC BK-channel expression was examined by immunohistochemistry and hearing function analyzed by auditory brain stem response measurements in AMPKα1-deficient mice (ampk-/-) and in wild-type mice (ampk+/+). As a result, coexpression of AMPK or AMPKγR70Q but not of AMPKαK45R significantly enhanced BK-channel-mediated currents and BK-channel protein abundance in the oocyte cell membrane. BK-channel expression in the inner ear was lower in ampk-/- mice than in ampk+/+ mice. The hearing thresholds prior to and immediately after an acoustic overexposure were similar in ampk-/- and ampk+/+ mice. However, the recovery from the acoustic trauma was significantly impaired in ampk-/- mice compared to ampk+/+ mice. In summary, AMPK is a potent regulator of BK channels. It may thus participate in the signaling cascades that protect the inner ear from damage following acoustic overstimulation.
细胞能量感受器 AMP 激活的丝氨酸/苏氨酸蛋白激酶 (AMPK) 通过刺激细胞能量产生和限制细胞能量利用来赋予细胞存活能力。AMPK 敏感的功能还包括上皮钠通道 ENaC 和电压门控钾通道 KCNE1/KCNQ1 的活性。AMPK 被增加的细胞质 Ca2+浓度激活。本研究探讨了 AMPK 是否调节 Ca2+敏感的大电导和电压门控钾 (BK) 通道。将编码 BK 通道的 cRNA 注入非洲爪蟾卵母细胞，同时或不额外注射野生型 AMPK (AMPKα1+AMPKβ1+AMPKγ1)、组成型激活的 AMPKγR70Q 或失活的 AMPKαK45R。利用双电极电压钳测定 BK 通道活性。此外，通过共聚焦免疫显微镜测定细胞膜上 BK 通道蛋白的丰度。由于 BK 通道在内耳的外毛细胞 (OHC) 中表达，并且缺乏 BK 通道会增加噪声易感性，因此通过免疫组织化学检查 AMPKα1 缺陷型 (ampk-/-) 小鼠和野生型 (ampk+/+) 小鼠中的 OHC BK 通道表达，并通过听觉脑干反应测量分析听力功能。结果，共表达 AMPK 或 AMPKγR70Q 但不表达 AMPKαK45R 显著增强了卵母细胞膜上的 BK 通道介导的电流和 BK 通道蛋白丰度。ampk-/- 小鼠内耳中的 BK 通道表达低于 ampk+/+ 小鼠。ampk-/- 和 ampk+/+ 小鼠在声过度暴露前后的听力阈值相似。然而，与 ampk+/+ 小鼠相比，ampk-/- 小鼠从声创伤中的恢复明显受损。总之，AMPK 是 BK 通道的有效调节剂。因此，它可能参与保护内耳免受声过度刺激损伤的信号级联反应。
