Slack sodium-activated potassium channel membrane expression requires p38 mitogen-activated protein kinase phosphorylation

- Slack KNa channel is subject to regulation by intracellular proteins.
- Two putative p38 MAPK phosphorylation sites reside in the Slack channel C terminus.
- Pharmacological modulation of p38 MAPK alters tonic KNa and Slack current.
- p38 MAPK regulates the Slack channel through direct phosphorylation at Serines 736 and S742.
- p38 MAPK phosphorylation is required for surface expression of the Slack channel.

p38 MAPK has long been understood as an inducible kinase under conditions of cellular stress, but there is now increasing evidence to support its role in the regulation of neuronal function. Several phosphorylation targets have been identified, an appreciable number of which are ion channels, implicating the possible involvement of p38 MAPK in neuronal excitability. The KNa channel Slack is an important protein to be studied as it is highly and ubiquitously expressed in DRG neurons and is important in the maintenance of their firing accommodation. We sought to examine if the Slack channel could be a substrate of p38 MAPK activity. First, we found that the Slack C-terminus contains two putative p38 MAPK phosphorylation sites that are highly conserved across species. Second, we show via electrophysiology experiments that KNa currents and further, Slack currents, are subject to tonic modulation by p38 MAPK. Third, biochemical approaches revealed that Slack channel regulation by p38 MAPK occurs through direct phosphorylation at the two putative sites of interaction, and mutating both sites prevented surface expression of Slack channels. Based on these results, we conclude that p38 MAPK is an obligate regulator of Slack channel function via the trafficking of channels into the membrane. The present study identifies Slack KNa channels as p38 MAPK substrates.