Tight junction structure in relation to transepithelial resistance in the frog choroid plexus.

In this communication we report observations on the tight junctions of the frog choroid plexus obtained by thin section and freeze-fracture electron microscopy. It is shown that the choroid plexus epithelial tight junctions comprise a relatively high number (mean 5-6, range 3-10) of continuous, anastomosing strands. This is remarkable in relation to: (1) recent observations that the frog choroidal epithelium has a very low transepithelial resistance, and (2) current concepts of the proportional relationship between transepithelial resistance and number of tight junction strands. It is concluded that there exists a marked lack of correlation between tight junction structure and function in the frog choroid plexus epithelium.