Hello everyone. I've been trying to understand the action of principal cells in the kidney collecting ducts in alkalosis. My professor told me that the activity of proton-potassium pumps in the basolateral membrane lead to high potassium concentrations in the principal cell and therefore lead to higher potassium secretion to the lumen. The confusing thing is, if the plasma has a low proton level, so should the filtrate in the lumen and the principal cell should have active proton-potassium pumps on the luminal surface as well. Which would lead to potassium intake from the lumen and proton secretion to the lumen. This contradicts my professor. Or is it that there are no proton-potassium pumps in the luminal surface? Or, there are such pumps on the luminal surface but the intake of potassium from the lumen contributes to high potassiu concentration in the cell and therefore subsequent secretion through regular potassium channels? I know this looks complicated but I would appreciate it if you tried. Many thanks.