Degradation and resynthesis of gap junction protein in plasma membranes of regenerating liver after partial hepatectomy or cholestasis

Publisher Website
Google Scholar
Abstract
Changes in the total amount of the gap junction protein (MW 26,000) after partial hepatectomy or bile duct ligation and recanalization were investigated in rat liver membranes by quantitative immunoblot with rabbit antiserum to the MW 26,000 protein. The loss and reappearance of the MW 26,000 protein roughly paralleled the loos and reappearance of gap junction plaques analyzed previously under similar physiological conditions by freeze-fracture of hepatocyte surfaces. The total amount of the hepatic MW 26,000 protein in liver plasma membranes and the total area of the hepatocyte surface occupied by gap junction plaques appeared to be proportional under these conditions. At the minimum, 28-35 h after partial hepatectomy, 15% of the MW 26,000 protein was still found, in contrast to < 1% of gap junction plaques, determined by morphometric analysis. This discrepancy is probably due to the fact that very small gap junction plaques, single connexons and free MW 26,000 gap junction subunits are missed by the morphometric analysis. At the times of the minimal amount of the MW 26,000 protein in hepatic plasma membranes after partial hepatectomy or bile duct ligation, it was found that crude hepatic lysosomal membranes of these rats contained less MW 26,000 protein than lysosomal membranes of nonoperated control animals. Thus, the decrease and increase of the total amount of the MW 26,000 protein apparently cannot be explained only by dispersal and reuse of gap junction subunits but are largely due to degradation and resynthesis of the MW 26,000 protein. No significant change in the amount of the MW 21,000 protein that had been isolated with gap junction plaques was observed in liver plasma membranes after partial hepatectomy. This confirms the previous conclusion that the MW 26,000 and MW 21,000 proteins are independent of each other.