Cellular electrophysiology of potassium transport in the mammalian cortical collecting tubule.

Electrophysiological studies were carried out on single perfused cortical and medullary collecting ducts to define the potassium and sodium transport properties of their apical and basolateral cell membranes. In addition, the effects of chronic mineralocorticoid hormone treatment on the mechanism of transport of potassium ions were evaluated. Studies included the measurement of transepithelial and cell potentials, and the resistance of individual cell membranes. The apical cell membrane of principal cells of the cortical collecting duct is characterized by separate potassium and sodium conductances. The basolateral cell membrane has also a potassium conductance, whereas the intercellular shunt pathway is largely permeable to chloride ions. Stimulation of potassium secretion by mineralocorticoids is associated with the following events. Increased cell potassium uptake across the basolateral cell membrane due to stimulation of Na-K ATPase and a more favorable electrical driving force for passive entry, facilitated exit of potassium from the cell to the tubule lumen by a more favorable electrochemical gradient (apical cell membrane depolarization) and enhanced potassium secretion by in increase of the potassium conductance of the apical cell membrane. Some properties of single potassium channels in the apical membrane of rabbit cortical collecting tubules are also described.