Modulation of K2P3.1 (TASK-1), K2P9.1 (TASK-3), and TASK-1/3 heteromer by reactive oxygen species

Reactive oxygen species (ROS) generated by mitochondria or NADPH oxidase have been implicated in the inhibition of K+ current by hypoxia in chemoreceptor cells. As TASKs are highly active background K+ channels in these cells, we studied the role of ROS in hypoxia-induced inhibition of TASKs. In HeLa cells expressing TASKs, H2O2 applied to inside-out patches activated TASK-1, TASK-3, and TASK-1/3 heteromer starting at ~16 mM. When applied to cell-attached or outside-out patches, 326 mM H2O2 did not affect TASK activity. Other K2P channels (TREK-1, TREK-2, TASK-2, TALK-1, TRESK) were not affected by H2O2 (tested up to 326 mM). A reducing agent (dithiothreitol) and a cysteine-modifying agent (2-aminoethyl methanethiosulfonate hydrobromide) had no effect on basal TASK activity and did not block the H2O2-induced increase in channel activity. A TASK mutant in which the C-terminus of TASK-3 was replaced with that of TREK-2 showed a normal sensitivity to H2O2. Xanthine/xanthine oxidase mixture used to generate superoxide radical showed no effect on TASK-1, TASK-3, and TASK-1/3 heteromer from either side of the membrane, but it strongly activated TASK-2 from the extracellular side. Acute H2O2 (32–326 mM) exposure did not affect hSlo1/b1(BK) expressed in HeLa cells and BK in carotid body glomus cells. In carotid body glomus cells, adrenal cortical cells, and cerebellar granule neurons that show abundant hypoxia-sensitive TASK activity, H2O2 (>16 mM) activated the channels only when applied intracellularly, similar to that observed with cloned TASKs. These findings show that ROS do not support or inhibit TASK and BK activity and therefore are unlikely to be the hypoxic signal that causes cell excitation via inhibition of these K+ channels.