Biophysical properties of hepatic cells: active sodium transport as a primary determinant of bile formation in the rat.

The importance of the biliary excretion of inorganic ions in bile formation was investigated. The distribution of erythritol-14C, inulin-3H, sodium, potassium and chloride between plasma, liver cells and bile was measured in rats with increased bile flow produced either by taurocholate infusion or by chronic administration of phenobarbital and decreased bile flow produced by acute ileal resection. Liver cell and bile duct potentials (PD) were measured in each animal. A 37.6 (±0.5 SEM) mV PD was recorded across the liver cell sinusoidal membrane (cell negative with respect to extracellular fluid). The PD across the liver cell canalicular membrane was estimated to be 32 mV (cell negative with respect to bile). The results demonstrate that sodium is actively transported out of the liver cell across the sinusoidal and canalicular membranes. Potassium is transported into the liver sell across these membranes. Based on the following observations the active transport of sodium into bile is considered to be the primary determinant of bile flow in the rat. 1) There is a large frication of bile flow which is bile salt-independent. 2) There is virtually no sodium-independent bile flow. 3) There is a close correlation between bile flow and sodium excretion. 4) Increasing sodium excretion increases bile flow independent of taurocholate excretion. 5) Increasing taurocholate excretion requires that sodium excretion also increases before an increase in bile flow can be observed. 6) The daily administration of phenobarbital (75 mg/kg) for 4 days increases bile flow and sodium excretion by 30%, whereas taurocholate excretion decreases by 46%.