*4.1. Animals*

C57/BL6J wild-type mice were used in this study. Kv4.2TA mice were generated as described before [42]. Mice were group housed in plastic mouse cages with free access to standard rodent chow and water. The colony room was maintained at 22 ± 2 ◦C with a 12 h: 12 h light: dark cycle. Kv4.2TA mice were backcrossed at least three generations onto C57/Bl6J mice. Age-matched male adult WT and

Kv4.2TA were used. All animal procedures were performed in accordance with guidelines approved by the *Eunice Kennedy Shriver* National Institute of Child Health and Human Development Animal Care and Use Committee and in accordance with NIH guidelines (20-042, 3 April 2020).

## *4.2. Expression Constructs*

The human Myc-DDK-Kv4.2 construct was purchased from Origene (Rockville, MD, USA, RC215266). The p38 construct was from Addgene (Watertown, MA, USA, 20351).
