CLONING OF A PH-SENSITIVE K+ CHANNEL POSSESSING 2 TRANSMEMBRANE SEGMENTS

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