Downregulation of Kv1.5 K+ Channels by the AMP-Activated Protein Kinase

Background: The voltage gated K+ channel Kv1.5 participates in the repolarization of a wide variety of cell types. Kv1.5 is downregulated during hypoxia, which is known to stimulate the energy-sensing AMP-activated serine/threonine protein kinase (AMPK). AMPK is a powerful regulator of nutrient transport and metabolism. Moreover, AMPK is known to downregulate several ion channels, an effect at least in part due to stimulation of the ubiquitin ligase Nedd4-2. The present study explored whether AMPK regulates Kv1.5. Methods: cRNA encoding Kv1.5 was injected into Xenopus oocytes with and without additional injection of wild-type AMPK (alpha 1 beta 1 gamma 1), of constitutively active (gamma R70Q)AMPK (alpha 1 beta 1 gamma 1(R70Q)), of inactive mutant (alpha K45)RAMPK (alpha 1(K45R)beta 1 gamma 1), or of Nedd4-2. Kv1.5 activity was determined by two-electrode voltage-clamp. Moreover, Kv1.5 protein abundance in the cell membrane was determined by chemiluminescence and immunostaining with subsequent confocal microscopy. Results: Coexpression of wild-type AMPK(WT) and constitutively active AMPK(gamma R70Q), but not of inactive AMPK(alpha K45R) significantly reduced Kv1.5-mediated currents. Coexpression of constitutively active AMPK(gamma R70Q) further reduced Kv1.5 K+ channel protein abundance in the cell membrane. Coexpression of Nedd4-2 similarly downregulated Kv1.5-mediated currents. Conclusion: AMPK is a potent regulator of Kv1.5. AMPK inhibits Kv1.5 presumably in part by activation of Nedd4-2 with subsequent clearance of channel protein from the cell membrane. Copyright (C) 2012 S. Karger AG, Basel