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Ion transport in collecting tubule principal cells

Ion transport in collecting tubule principal cells
Schematic representation of sodium (Na) and potassium (K) transport in the sodium-reabsorbing principal cells in the collecting tubules. The entry of filtered sodium into these cells is mediated by selective sodium channels in the apical (luminal) membrane (ENaC); the energy for this process is provided by the favorable electrochemical gradient for sodium (cell interior electronegative and low cell sodium concentration). Reabsorbed sodium is pumped out of the cell by the Na-K-ATPase pump in the basolateral (peritubular) membrane. The reabsorption of cationic sodium makes the lumen electronegative, thereby creating a favorable gradient for the secretion of potassium into the lumen via potassium channels (ROMK and BK) in the apical membrane. Aldosterone (Aldo), after combining with the cytosolic mineralocorticoid receptor (Aldo-R), leads to enhanced sodium reabsorption and potassium secretion by increasing both the number of open sodium channels and the number of Na-K-ATPase pumps. The potassium-sparing diuretics (amiloride and triamterene) act by directly inhibiting the epithelial sodium channel; spironolactone acts by competing with aldosterone for binding to the mineralocorticoid receptor.
Graphic 60693 Version 16.0

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