Formation of actin filament networks in cultured rat hepatocytes treated with DMSO and glucagon.

Actin filament organization may play an important role in the maintenance of differentiated functions in epithelial cells. We previously reported our success in inducing and maintaining gap junctions, which are two kinds of differentiated function, in primary rat hepatocytes cultured with 2% DMSO and 10-7 M glucagon. In the present study, we demonstrated the formation of actin filament networks in the hepatocytes cultured with 2% DMSO and 10-7 M glucagon. Actin filaments in hepatocytes cultured in medium with only 2% DMSO added from 96 h after plating were concentrated under the plasma membrane and were observed to be circumferential. In hepatocytes cultured in the medium with both 2% DMSO and 10-7 M glucagon added from 96 h, not only the circumferential actin filaments but also the formation of actin filament networks were observed and the networks developed well with time in culture. The networks were observed as a dome-like structure under the cell face and terminated at the circumferential actin filaments. They were composed of electron-dense star-like vertices connected by microfilament bundles of varying length and were also very sensitive to the actin disruptor cytochalasin B. However, during the network formation, there were no significant increases in the amounts of actin protein and mRNA. The actin filament networks of the hepatocytes in this culture system might be closely related to the maintenance of differentiated functions.