Membrane structure in cultured astrocytes.

Astrocytes cultured from the brains of neonatal rat pups acquire at least two specializations of intramembrane particle distribution: 'assemblies' and gap junctions. The number and appearance of assemblies in the cultured astrocytes is not markedly influenced by the presence or absence of a collagen substrate, and the range of concentrations of assemblies in astrocytic membranes is fairly stable from 7 through 28 days in culture. The assemblies are not concentrated in apposition to the substrate, even though the astrocytic membranes containing the highest concentration of assemblies in vivo are apposed to basal lamina. Quantitative analysis shows that assemblies are not uniformly distributed over the plasmalemma of a single cell, raising the possibility that the nature of cells around an astrocytic process may influence its membrane composition in vitro.