Aggregated plasmalemmal vesicles and microvilli in human astrocytoma.

Plasmalemmal vesicles and microvilli or filopodia in human astrocytoma were examined with thin-section and freeze-fracture techniques. The plasmalemmal vesicles, although sparsely scattered in distribution, were often aggregated in a curvilinear, semicircular, or circular fashion, and the involved plasma membrane was often protruded externally like a mound. Microvilli or filopodia were cross-fractured when fracture travelled within the plasma membrane resulting in a fracture face interrupted by numerous holes of cytoplasms. The microvilli were distributed in a concentrated manner on the free surface of the cell and often closely oriented in a linear, curvilinear, or circular fashion. They varied in size, form, and length. When they were arisen from a common hillock of the plasma membrane, its fracture face was elongated, up to 0.8 mu in length. Fenestrae were occasionally visible in attenuated cytoplasm which surrounded peripheral vacuole in the cell.