Pore-forming (alpha) subunit of voltage-gated rapidly inactivating A-type potassium channels. May contribute to I(To) current in the heart and I(Sa) current in neurons. Channel properties are modulated by subunit assembly. 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.