Figure 119

Mechanism of sodium chloride reabsorption in collecting duct cells. Sodium transport in the collecting duct is mainly via amiloride-sensitive sodium channels in the apical membrane. Some evidence for other mechanisms such as an electroneutral sodium-chloride cotrans-port mechanism and a different sodium channel also has been reported. Again, the basolateral sodium-potassium ATPase (Na+-K+ ATPase) creates the driving force for overall sodium transport. There are some differences between the cortical collecting duct and the deeper inner medullary collecting duct (IMCD). In the cortical collecting duct, sodium transport occurs in the predominant principal cell type interspersed between acid-base transporting intercalated cells. The principal cell also is an important site of potassium secretion by way of apical potassium channels and water transport via antidiuretic sensitive water channels. Regulation of sodium channels may involve either insertion (from subapical compartments) or activation of preexisting sodium channels.

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