Electron microscopy: sodium localization in normal and ouabain-treated transporting cells.

When rabbit corneas are fixed in an osmic acid fixativeto which potassium pyroantimonate has been added, an electron-opaque precipitate of sodiium pyroantimonate is localized along the cellular side of the lateral plasmla membrane of the endothelial cells. This heavy precipitate represents areas of high Na(+) concentration and may represent the site of a saturated, high-affinity Na(+) carrier. Significantly heavier precipitate occurs at the same site when ouabain is injected into the aqueous humor prior to fixation of the cornea.