Ca2+ causes active contraction of bile canaliculi: direct evidence from microinjection studies.

Cytoplasmic microinjection of Ca2+ triggers contraction of bile canaliculi in freshly isolated monolayer cultures of rat hepatocytes. Unseparated paired hepatocytes were used to demonstrate this motility-based phenomenon. Only one cell of the pair was injected, but fluorescein spread from the target cell to the opposite cell; also, the contractions were always uniform, equally involving both hepatocytes that form the canaliculus, indicating that communication exists between the cell pairs. Inhibitors of calmodulin and actin filaments, trifluoperazine and cytochalasin B, respectively, inhibited the Ca2+-induced contractions. Hence, the mechanism of contraction has features in common with actin-myosin based cytoplasmic motility behavior found in other non-muscle cells.