Intracellular polycationic molecules cause reversible swelling of the rough endoplasmic reticulum

The microinjection of polycationic but not anionic molecules causes swelling of the rough endoplasmic reticulum (RER) in salivary gland cells of a fly larva. Ca-EGTA buffers, lanthanum chloride, lysozyme, bovine serum albumin, cationic and anionic ferritin were microinjected into salivary gland cells and their effects observed by light and electron microscopy. Immediately after the microinjection of polycationic molecules, the cytoplasm changed from transparent to opaque as the RER became swollen. Binding of polycationic molecules to the RER may cause the membrane to become permeable to some solute and swell due to osmotic forces.