Pore-forming (alpha) subunit of voltage-gated rapidly inactivating A-type potassium channels. May contribute to I(To) current in heart and I(Sa) current in neurons. Channel properties are modulated by interactions with other alpha subunits and with regulatory subunits. Homotetramer or heterotetramer with KCND1 and/or KCND2. Associates with the regulatory subunits KCNIP1, KCNIP2, KCNIP3 and KCNIP4. Interacts with DLG1, KCNE1, KCNE2, SCN1B and KCNAB1 (By similarity). Interaction with palmitoylated KCNIP2 and KCNIP3 enhances cell surface expression. The segment S4 is probably the voltage-sensor and is characterized by a series of positively charged amino acids at every third position. Regulated through phosphorylation at Ser-569 by CaMK2D. May be due to intron retention. Belongs to the potassium channel family. D (Shal) (TC 1.A.1.2) subfamily. Kv4.3/KCND3 sub-subfamily.