The patch-clamp technique has made it possible to de® ne not only the biophysical properties and localization of K channels along the nephron but also to gain insight into the factors that control their activity and their role in transport processes. In addition, advances in the cloning of K channels of renal origin have made it possible to determine their molecular structure and the relationship of the structure of channel proteins to their function. The de® nition of the structure of the ATP-sensitive K channels in renal tubules has also led to insights into the mechanism of the inherited renal disorder known as Bartter's syndrome.

Not only do K channels play an important role in the process of K secretion but they are also involved in the mechanism by which tubule cells maintain uid and electrolyte equilibrium. Firstly, K channels participate in the generation of the cell-negative potential that provides an important driving force for the movement of charged solutes across both apical and basolateral membranes of tubule cells. Several K channels in proximal and distal tubule cells contribute to the conductance of the basolateral membranes and their activity has been shown to determine the magnitude of the cell membrane potential (Giebisch 1995, 1999, Wang et al. 1997a, b, Giebisch et al. 2000, Wang & Hebert 2000).