Pump leak model

The pump leak model is a mechanism for the reabsorption of sodium in the kidney nephrons (in order to achieve the euvolemic state)

Pump - active transport of sodium from the tubular cell into the interstitial space (at the basolateral membrane) via carrier proteins (i.e. Na+/K+ ATPase)

Leak - the action of active transport (of the Na+/K+ ATPase) creates a diffusion gradient that opposes its own action by favouring back-diffusion.

Sodium is passively transported from the tubular fluid into the tubular cells at the apical membrane (via ion channels), and then actively pumped out of the tubular cells at the basolateral membrane (via Na+/K+ ATPase), which then enters the blood.