THE mammalian renal collecting ducts are responsible for secreting potassium ions into the urine and are a major regulatory site for potassium homeostasis(1), in which a voltage-independent pH-sensitive K+ channel in the apical membrane plays a central role(2,3). Here we describe a complementary DNA encoding a novel K+ channel from rabbit renal cortical collecting tubule cells (RACTK1). RACTK1 has the functional characteristics of the apical K+-permeable channel and consists of 284 amino acids, putatively with two transmembrane segments. The sequence of RACTK1, however, shows no homology to known voltage-dependent or -independent K+ channels, and has a different K+-driving path and regulatory sites, The study of this protein should provide insight into K+ homeostasis and diseases of K+ metabolism.