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 (α1 β1γ1), of constitutively active ^γR70QAMPK (α1 β1γ1(R70Q)), of inactive mutant ^αK45RAMPK (α1(K45R)β1γ1), or of the ubiquitin ligase 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^γR70Q, but not of inactive AMPK^αK45R signifcantly reduced Kv1.5-mediated currents. Coexpression of constitutively active AMPK^γR70Q further reduced Kv1.5 K⁺ channel protein abundance in the cell membrane. Co-expression of Nedd4-2 similarly downregulated Kv1.5-mediated currents.

Conclusions:

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.