Cationic Ferritin Labeling Of Anionic Sites At Cellular Surfaces

Cationic and anionic ferritins were used to map the distribution of charged sites on intracellular and extracellular surfaces. The distribution of tracers at cell surfaces and injected into live cells was examined by electron microscopy.;The distribution of microinjected ferritin showed that intracellular surfaces are negatively charged. Highly cationic ferritins (HCF pI \u3e 9) were mostly bound to and caused swelling of the rough endoplasmic reticulum. Cationic ferritin (CF pI 7.0-8.0) and anionic ferritin (AF pI 4.0-4.4) caused no changes in morphology. Ferritin distribution in the cytoplasmic space varied with its charge. Significantly more CF was bound to surfaces than was found in the free cytoplasmic space. Comparison of the structures in the secretory pathway showed that there were no significant differences in the amount of CF (pI 7.0-8.0) bound. The Golgi complex beads were not distinguished by their charge. Differences in charge do not regulate membrane-membrane interactions in the secretory pathway.;The microinjection of cationic but not anionic molecules causes swelling of the rough endoplasmic reticulum. Calcium buffers, lanthanum chloride, lysozyme, bovine serum albumin and 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 rough endoplasmic reticulum became swollen. Binding of polycationic molecules to the rough endoplasmic reticulum may cause the membrane to become permeable to certain solutes and swell due to osmotic forces.;Clusters of anionic sites, labeled by HCF, are present throughout the basal lamina. The penetration of ferritins through the basal lamina into the spaces between fat body cells varies with the charge of the tracer. Cationic ferritins penetrated the basal lamina and bound to anionic sites on membrane surfaces. Little anionic ferritin was found in the spaces surrounding the fat body. The basal lamina therefore acts like a negatively charged sieve to control the composition of the fluid that bathes the fat body cells. More CF was bound to the membranes of the plasma membrane reticular system than to the lateral plasma membrane, suggesting that there are regional differences in surface charge