The AMPK activator A-769662 inhibits human TASK3 potassium channels in an AMPK-independent manner
Heteromeric TASK1/3 channels play a fundamental role in oxygen-sensing by carotid body type 1 cells, where hypoxia-induced inhibition of TASK3 and/or TASK1/3 potassium currents leads to depolarisation, voltage-gated calcium entry, exocytotic transmitter release and increases in carotid body afferent input responses that initiate corrective changes in breathing patterns. However, the mechanism by which hypoxia leads to TASK-1/3 channel inhibition is still debated. It had been proposed that the AMP-activated protein kinase (AMPK) might directly phosphorylate and inhibit TASK channels, in particular TASK-3, although subsequent studies on rat type I cells argued against this view. Here we report on the effects of novel, highly selective AMPK activators on recombinant human TASK-3 potassium channels. Sequence alignment identified an AMPK recognition motif in TASK-3, but not TASK-1, with Ser55 representing a potential site for AMPK-dependent phosphorylation in TASK-3. However, neither of the AMPK activators, AICAR or MK-8722, caused a significant reduction of human TASK-3 current amplitude. By contrast, high concentrations of the AMPK activator A-769662 (100-500 {micro}M) inhibited human TASK-3 currents in a concentration-dependent manner. Importantly, A-769662 (300 {micro}M) also inhibited human TASK-3 channels in HEK293 cells that stably over-expressed an AMPK-{beta}1 subunit mutant (S108A) that renders AMPK insensitive to activators binding the Allosteric Drug and Metabolite (ADaM) site, such as A-769662. We therefore identify A-769662 as a novel human TASK-3 channel inhibitor and provide conclusive evidence that AMPK does not regulate TASK-3 channel currents.