Isolated Rat Hepatocyte Couplets: A Primary Secretory Unit for Electrophysiologic Studies of Bile Secretory Function

Hepatocyte couplets were isolated by collagenase perfusion from rat liver. Between adjacent cells, the bile canaliculus forma a closed space into which secretion occurs. As in intact liver, Mg²⁺-ATPase is localized at the canalicular lumen, the organic anion fluorescein is excreted, and secretion is modified by osmotic gradients. By passing a microelectrode through one cell into the canalicular vacuole, a transepithelial potential profile was obtained. In 27 cell couplets the steady-state intracellular (-26.3 ± 5.3 mV) and intracanalicular (-5.9 ± 3.3 mV) potentials were recorded at 37 degrees C with reference to the external medium. Input resistances were determined within the cell (86 ± 23 MΩ ) and in the bile canalicular lumen (32 ± 17 MΩ ) by passing current pulses through the microelectrode. These data define electrical driving forces for ion transport across the sinusoidal, canalicular, and paracellular barriers and indicate ion permeation across a leaky paracellular junctional pathway. These findings indicate that the isolated hepatocyte couplet is an effective model for electrophysiologic studies of bile secretory function.