Surface structures of cultured type 2 astrocytes revealed by atomic force microscopy

The incomplete morphological characterization of type 2 astrocytes is in pa ri responsible for the slow progress of studies on these cells. To examine and characterize type 2 astrocytes morphologically, three-dimensional fine structures of the surfaces of type 2 astrocytes cultured from rat cerebella were studied by a combination of atomic force microscopic and immunocytoch emical techniques. Atomic force microscopy (AFM) revealed irregular ridge-l ike structures that form a meshwork distributed throughout the cell body su rfaces and the thick processes. These ridges were found to be of two height s (31 nm and 82 nm). This finding indicates two possible configurations res ponsible for shaping the meshwork: (1) two structures of different thicknes s are beneath the cell membrane; and (2) two structures are located at two different depths from the cell membrane. On the other hand, immunocytochemi cal studies for tubulin and glial fibrillary acidic protein (GFAP) revealed that these cytoskeletal filaments are similarly distributed within the res olution power of a light microscope. However, no detectable structures were obtained by actin staining. The immunocytochemical findings suggest that t he AFM-revealed ridges forming the irregular meshwork on the cell surfaces may reflect very fine bundles of tubulin and/or GFAP. Therefore, AFM study, with the help of immunocytochemical study, is a powerful tool for characte rizing cell morphology. The results of the present study reveal the first m orphological characterization of type 2 astrocytes.