Cell membrane structure of human giant-celled glioblastoma.

A giant-cell glioblastoma was examined by electron microscopy and by the freeze-fracture technique. The cell membranes bordering the extensive extracellular space often showed complicated undulations and peripheral vacuoles as well as occasional microvilli or filopodia. The undulations were mainly composed of plasmalemmal vesicles as well as of large (400--800 nm in diameter) and small (30--50 nm in diameter) localized protrusions and invaginations of the cell membrane. Deep invaginations of the cell membrane apparently resulted in two separate cytoplasmic portions. Locking of protruded cytoplasmic tongues and adherens junctions were sometimes seen in closely approximated cell membranes. The average number of membrane particles per micrometer2 was 630 +/- 130 on the P face and 180 +/- 30 on the E face. The membrane particles were occasionally aggregated to form clusters about 30 to 150 micrometer in diameter. Gap junctions were occasionally found, but there were no tight junctions. Large particles about 30 nm in diameter were found in places.