Cloning of a pH sensitive K+ channel in the kidney

The renal collecting tubules are responsible for secretion of K+ into the urine and play a major regulatory role in K+ homeostasis of mammals. There are several factors which affect K+ secretion, including aldosterone, K intakes and acid-base balance. We have cloned a complementary DNA encoding a K+ channel of the rabbit renal cortical collecting tubule cells (RACTK1). RACTK1 is a voltage-independent, pH sensitive K(+)-permeable channel, encoding 284 amino-acids, and putatively having two transmembrane segments. This channel is located not only in the luminal membrane of the collecting duct but also in the vascular smooth muscles of the several arteries. The expression of RACTK1 is regulated by external pH but neither by aldosterone nor by K+ concentration in cultured cells. Thus RACTK1 seems to be a unique and distinct from K+ channels in that it is regulated specifically by changes in ambient pH, contributing to the pH dependent urinary K+ excretion.