The intracellular localization of inorganic cations with potassium pyroantimonate. Electron microscope and microprobe analysis

Inorganic cations in rat kidney. Localization with potassium pyroantimonate--perfusion fixation

For localization of pyroantimonate-precipitable cations, rat kidney was fixed by perfusion with a saturated aqueous solution of potassium pyroantimonate (pH about 9.2, without addition of any conventional fixative). A remarkably good preservation of the tissue and cell morphology was obtained as well as a consistent and reproducible localization of the insoluble antimonate salts of magnesium, calcium, and sodium. All proximal and distal tubules and glomeruli were delimited by massive electron-opaque precipitates localized in the basement membrane and, to a lesser extent, in adjacent connective tissue. In the intraglomerular capillaries the antimonate precipitate was encountered in the basement membranes and also between the foot processes. In addition to a more or less uniform distribution in the cytoplasm and between the microvilli of the brush border, antimonate precipitates were found in all cell nuclei, mainly between the masses of condensed chromatin. The mitochondria usually contained a few large antimonate deposits which probably correspond to the so-called "dense granules" observed after conventional fixations.

The distribution of inorganic cations in mouse testis. Electron microscope and microprobe analysis

For localization of pyroantimonate-precipitable cations, mouse testes were fixed with a saturated aqueous solution of potassium pyroantimonate (pH about 9.2, without addition of any conventional fixative), hardened with formaldehyde, and postosmicated. A good preservation of the cell membranes and over-all cell morphology is obtained as well as a consistent and reproducible localization of the insoluble antimonate salts of magnesium, calcium, and sodium. Four sites of prominent antimonate deposits are revealed, besides a more or less uniform distribution of the precipitates. These sites are: (a) In the walls of the seminiferous tubules, localized in two concentric layers corresponding to the inner and outer layers of the tubular wall; (b) Around the blood vessels and adjacent connective tissue; (c) At the area of contact between the Sertoli cell and spermatids, where a double line of precipitate surrounds the head of the mature spermatids; and (d) In the cell nuclei, disposed between regions of the condensed chromatin. The nucleus of mature spermatids did not show any sign of antimonate precipitation. The implications of this inorganic cation distribution are discussed with relation to their anionic counterparts, their localization in other animal and plant tissues, and the possibility that those sites may represent barriers to the free passage of ions.

The septate junction: a structural basis for intercellular coupling

Electron microscopy, freeze-etching, and optical diffraction show how the structure of the septate junction may provide the basis for the low-resistance pathway between the electrically coupled cells in mussel gill epithelia. Conventional electron microscopy suggests that the septa are pleated sheets that differentiate from and are structurally continuous with the junctional cell membranes. Freeze-etching exposes geometrically arranged rows of 85-A particles within the junctional cell membranes. Diffraction evidence shows that these membrane particles and the alternate vertices of the intercellular septal sheets are congruent and therefore superposable. Together, the membrane particles and septal sheets provide a channel that extends from the cytoplasm of one cell through the septate junction to the cytoplasm of the adjacent cell.