AMP-activated protein kinase in BK-channel regulation and protection against hearing loss following acoustic overstimulation

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 (AMPK alpha 1 + AMPK beta 1 + AMPK gamma 1), constitutively active AMPK(gamma R70Q), or inactive AMPK(alpha K45R). 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 AMPK alpha 1-deficient mice (ampk(-/-)) and in wild-type mice (ampk(+/+)). As a result, coexpression of AMPK or AMPK(gamma R70Q) but not of AMPK(alpha K45R) 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.-Fuller, M., Jaumann, M., Dettling, J., Saxena, A., Pakladok, T., Munoz, C., Ruth, P., Sopjani, M., Seebohm, G., Ruttiger, L., Knipper, M., Lang, F. AMP-activated protein kinase in BK-channel regulation and protection against hearing loss following acoustic overstimulation. FASEB J. 26, 4243-4253 (2012). www.fasebj.org