Does Na+-K+-atpase have any role in bile secretion?

Abstract

In this review, I have attempted to summarize the evidence supporting the view that Na+-K+-ATPase (the enzymatic basis for the sodium pump) plays a key role in bile secretion. First, experiments in the isolated perfused liver, in isolated and cultured hepatocytes, and more recently in hepatocyte membrane vesicles strongly suggest that bile acid uptake by the hepatocyte is a secondary active transport that is energized by the Na+ gradient maintained by the Na+-K+-ATPase. Thus, Na+-K+-ATPase appears important in coupling the energy from ATP to transport activity, resulting in the so-called bile acid-dependent bile flow. Second, experiments with liver plasma membranes have shown a correlation between Na+-K+-ATPase activity in these preparations and the so-called bile acid-independent bile flow. In view of the recognized sinusoidal-lateral localization of the Na+-K+-ATPase in the liver cells, several possibilities are proposed to explain how the enzyme activity could be coupled to ion transport and secretion into bile. These possibilities include Na+ movement from the intercellular space into the canalicular lumen through the paracellular pathway and movement of another ion using the Na+ gradient.