An unusual membrane specialization of mammalian cells in vitro

An unusual membrane specialization, termed "particle rows," was revealed by freeze-fracture electron microscopy in cultured mammalian cells including dissociated central nervous system tissue and peripheral connective tissue. The specialization consisted of rows of particles slightly elevated on the P fracture face, with a regular periodicity of 35 nm between the rows and a uniform length of the rows of 100 nm. It was usually associated with caveolae (pits) and sometimes accompanied gap junctions, or tight and gap junctional complexes within the same membrane. The particle rows are probably expressed by more than one cell type, all in immature form.