Ultrastructural Changes of the Cultured Hepatocytes in Microfilamentous Dysfunction induced by Drugs

Kim, Jin Gook; Ko, Jeong Sik; Ahn, E Tay; Park, Kyung Ho

Abstract

To examine the role of actin microfilaments which are located at beneath the plasma membrane, we observed the ultrastructural changes of rat hepatocyte induced by alteration of the microfilamentous integrity. The isolated hepatocytes from Sprague-Dawley were cultured in the L-15 medium containing phalloidin (agent that cause polymerization of actin) or cytochalasin D (agent that cause depolymerization of actin) for 30 min, 1 hour, 2 hours, 4 hours, 10 hours and 20 hours, respectively. The results observed with scanning and transmission electron microscope were as follows. 1. Following the alteration of actin microfilaments, bile canaliculi were dilated and devoid of microvilli. In phalloidin treated group, the thickening of microfilamentous ectoplasm was more marked than that of cytochalasin D treated group. Whereas, the dilation of bile canaliculi was more marked in cytochalasin D group. 2. Both drugs, phalloidin or cytochalasin D, produced the alteration of cell shape to form cytoplasmic protrusions at the cell surface. In the phalloidin treated group, protrusions were pedunculated, and the microfilament networks were accumulated at the narrow neck region. 3. In cytochalasin D treated group, no microfilament barrier was seen at the broad base of protrusion which exhibit direct continuity with the internal cytoplasm. 4. Single hepatocyte tend to recover their structural integrity as those in vivo. The new bile canaliculus was sealed off at the intercellular space by tight junctions, and intercellular contacts were established by the junctional complexes. The results demonstrated that excessive accumulation or depletion of microfilaments induced by phalloidin or cytochalasin D altered the cell shape different, respectively. The microfilaments of ectoplasm play an important role in the maintenance of the structural integrity of cultured hepatocytes.