Effect of monensin on cell ultrastructure and glycoprotein migration in adult mouse jejunal epithelium in organ culture.

Explants from adult mouse jejunum were cultured for 3 h in a medium which contained both 3H-fucose (10 or 25 microCi/ml) and monensin (100 microM) or 3H-fucose only (control). Radiochemical analysis of cell fractions showed that 3H-fucose labelling of the brush border fraction decreased 42% in monensin-treated explants, suggesting that in absorptive cells the intracellular transport of newly synthesized glycoproteins to the apical plasma membrane had been inhibited. Electron-microscopic examination of treated explants revealed a variation in response to the drug from region to region. In some areas, both absorptive and goblet cells exhibited little alteration. In others, the Golgi cisternae of both absorptive and goblet cells were entirely replaced by large vacuoles, and in the latter cell type, the cisternae of the rough endoplasmic reticulum were greatly distended. Electron-microscopic radioautographic analysis showed that in absorptive and goblet cells exhibiting little morphological change, intracellular transport of newly synthesized glycoproteins was similar to that in controls. In regions where absorptive cells exhibited extensive Golgi modifications, intracellular transport remained normal in some cases; more often-however, there was a marked inhibition (over 70%) of transport of labelled glycoproteins to the apical surface. Transport to the basolateral membrane was never affected. In goblet cells exhibiting modifications of the Golgi apparatus and rough endoplasmic reticulum, no incorporation of 3H-fucose label in the Golgi apparatus occurred, suggesting a block of intracellular transport proximal to the site at which 3H-fucose is added. In absorptive cells, this does not appear to be the case, since the level of 3H-fucose incorporation in all treated cells remained similar to that in controls.