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 (By similarity). Homotetramer or heterotetramer with KCND2 and/or KCND3. Associates with the regulatory subunits KCNIP1, KCNIP2, KCNIP3 and KCNIP4. Interacts with DPP10 (By similarity). The segment S4 is probably the voltage-sensor and is characterized by a series of positively charged amino acids at every third position. Belongs to the potassium channel family. D (Shal) (TC 1.A.1.2) subfamily. Kv4.1/KCND1 sub-subfamily.