Ultrastructure of cultured marginal cells of the guinea pig cochlea.

Explants of stria vascularis and spiral ligament of guinea pig cochlea were kept in primary culture. On the explant, proliferating marginal cells advanced by 15 microns/day, suggesting that in vivo defects of the strial epithelium can be covered by new marginal cells. The marginal cells growing in the cell culture dish had a diameter of 12.8 +/- 0.7 microns and formed an epithelial monolayer. Adjacent cells were connected by desmosomes and tight junctions. The cells were uniformly polarized. The apical membrane had small invaginations and numerous microvillus-like extensions, and the convoluted lateral membrane interdigitated with adjacent cells. The basal infoldings were smaller in cultured cells than in vivo; mitochondria were dispersed in the entire cytoplasm rather than concentrated in basolateral infoldings. The basal membrane infoldings of cultured marginal cells did not interdigitate with underlying fibroblast-like cells. Marginal cells were separated from underlying fibroblast-like cells by a fluid-filled space which was sometimes enlarged, leading to the formation of "domes" in the otherwise planar epithelium.