Intracellular distribution of glycogen synthase and glycogen in primary cultured rat hepatocytes

Changes in the intracellular distribution of liver glycogen synthase (GS) m ight constitute a new regulatory mechanism for the activity of this enzyme at cellular level. Our previous studies indicated that incubation of isolat ed hepatocytes with glucose activated GS and resulted in its translocation from a homogeneous cytosolic distribution to the cell periphery. These stud ies also suggested a relationship with insoluble elements of the cytoskelet on, in particular actin. Here we show the translocation of GS in a differen t experimental model that allows the analysis of this phenomenon in long-te rm studies. We describe the reversibility of translocation of GS and its ef fect on glycogen distribution. Incubation of cultured rat hepatocytes with glucose activated GS and triggered its translocation to the hepatocyte peri phery. The relative amount of the enzyme concentrated near the plasma membr ane increased with time up to 8 h of incubation with glucose, when the glyc ogen stores reached their maximal value. The lithium-induced covalent activ ation of GS was not sufficient to cause its translocation to the cell perip hery. The intracellular distribution of GS closely resembled that of glycog en, Our results showed an interaction between GS and an insoluble element o f the hepatocyte matrix. Although no colocalization between actin filaments and GS was observed in any condition, disruption of actin cytoskeleton res ulted in a significantly lower percentage of cells in which the enzyme tran slocated to the cell periphery in response to glucose. This observation sug gests that the microfilament network has a role in the translocation of GS.