Cytochalasin B affects the gap and tight junctions of mouse hepatocytes in vivo.

This study investigates the effect of cytochalasin B at a dosage of 0.2 mg per mouse per day for a period of 7 days in an in vivo experiment on mouse liver. Using thin-sectioning and freeze-fracture technique both quantitative and qualitative analysis was made of membranes and cell contacts (gap and tight junctions). Significant alterations of both membranes and junctions were observed. The intercellular space showed vacuolar dilatation in some cases and there were vacuoles observed within the cytoplasm. The microvillar bile canaliculi were dilated. However, no colloidal tracer was observed within the lumen following lanthanum perfusion. With the aid of the freeze-fracture method it was possible to demonstrate that the strands of the tight junctions were highly disorganized. In some cases reduction and in other cases proliferation of tight junctions was observed. Large, proliferative plaques of tight junctions were found both in contact with the tight junctions of the bile canaliculus and ending freely on the plasmalemma. The gap junctions appeared enlarged as well. Their average size increased from 0.42 micron 2 to 0.90 micron 2 (p less than 0.005). The enlargement was also accompanied by an increase in the proportion of the plasma membrane occupied by the junctions: 3.42% in control animals, 10.25% in the livers of mice treated with cytochalasin B. Frequently evaginated and internalized gap junctions were seen in the experimental group. In view of the fact that cytochalasin B, in addition to other effects, also has an effect on the microfilament system of the cell, it may be supposed that microfilaments play a role in maintenance of the orderly structure or in the formation of tight and gap junctions. This remains hypothetical, however, and additional studies are necessary in order to conclusively clarify this issue.