Morphological characterization of the plasma membrane of a pituitary tumor cell line (GH3).

Freeze-fracturing and deep-etching have been used to characterize the internal morphology and surface charge of the plasma membrane of GH3-cells from cell culture in fixed and unfixed material. Glutaraldehyde does not effect intramembrane particle pattern but induces structural modifications on the cell surface in a way that additional attachment sites for cationized ferritin are exposed at specific areas of the membrane. Negative surface charges are not directly linked to the intramembrane particles, but to other (surface-) proteins, independently enough to be dislocated by external ligands; this process is restricted to the membrane surface. Thermotropic phase changes induce separation of lipidic regions from proteinaceous regions. Peripheral and integral protein are thus aggregated simultaneously, resulting in clustered membrane particles and aggregated surface charges.