Surface extensions on bhk cells grown in monolayers and agar suspension

Three types of surface extensions found on a subline of BHK cells capable of growing in agar are described. These are:Microvilli-borne on the cell surface, lacking rigid cores, found on trypsinized cells and on cells growing in solid tissue type growth;Microspikes-borne on the cell margins, containing rigid cores, found on spread, attached cells, but not trypsinized cells or cells growing in solid tissues;Retraction fibrils-coreless ‘passive’ cell extensions drawn out distally as motile cells move across a surface. Microvilli also seem to be associated with micropinocytic vesicles. It is suggested that microvilli on tissue cells in vitro may be homologous with the cell membrane interdigitations found in, for example, gut epithelium, and possibly also with the microvilli of brush borders. Their association with these structures suggests they may play a role in producing a local environment near the cell membrane in which micropinocytosis may function more effectively.