Bile canalicular membrane pathology in cytochalasin B-induced cholestasis.

The mechanism of cytochalasin B-induced intrahepatic cholestasis was examined using electron cytochemical techniques. Since previous studies suggested that the earliest lesions were in hepatic canaliculi, markers were used for three canalicular membrane components, namely ruthenium red for the glycoprotein-rich surface coat, the Mg2+-ATPase reaction as an example of a membrane-bound protein, and uranyl acetate en bloc and ruthenium red staining for the canalicular membrane-associated microfilaments. In rat liver infused in vivo with cytochalasin B, reduction in bile flow correlated with bile canalicular dilation, loss of the ruthenium red-positive surface coat from the canalicular membrane, and loss of demonstrable Mg2+-ATPase activity. In addition, structural alterations in microfilaments with widening of the ectoplasmic zone were noted. In isolated liver cells in vitro, identical changes were found. Bile canaliculi isolated from the in vivo cytochalasin B-infused rat liver lacked their normal investment of microfilaments. Detachment of the filaments from the bile canalicular membrane may be involved in the mechanism of cytochalasin B-induced cholestasis.