Ouabain-mediated sodium uptake and bile formation by isolated perfused rat liver

Ouabain exhibits a dose-dependent choleretic effect in the isolated perfused rat liver. Its uptake from the perfusate into the liver is maintained against a concentration gradient and becomes clearly saturated at higher perfusate concentrations. A low extracellular sodium concentration inhibits the rate of ouabain transfer into liver cells, resulting in a marked decrease of the maximal transport rate. Dibucaine completely abolishes the uptake of the glycoside by the isolated liver. Determination of Na-22 tracer fluxes suggests that ouabain uptake is accompanied by a net flux of sodium into the cell, which seems to be due to a cotransport of sodium with ouabain rather than to the inhibition of the sinusoidal Na+ -K+ -ATPase. Sodium introduced into the cell in this way apparently is extruded into the bile canaliculi. The increase of isotonic bile flow, which is simultaneously observed, points to a dilution of the canalicular sodium gradient by water and electrolytes through an intercellular pathway. Our results present further evidence that bile secretion is controlled by transcellular sodium movements.