English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The structure and function of the gap junction has become a modern, cell biological problem of extreme interest in view of physiological studies suggesting that the gap junction mediates an intercellular communication, creating metabolic and electrical coupling between adjacent cells (2) . The most significant point in the model of the gap junction is a continuous, hydrophilic channel, transversing both junctional membranes, although electron micrographs showing a direct evidence of such a channel are limited. In this report we tried to visualize the channel under an electron microscope using alkali-metal ions such as Cs+ or Rb+ served as a physiological isotope for K+ and an electron microscopic observation revealed dense precipitates within the gap junction, suggesting that the gap junction is involved in the intracellular ion transport. The ultrastructure of the gap junction has been examined by the thin sectioning technique, negative staining and freeze-replica methods which have shown that it is composed of packed arrangements of 8-9 nm particles, called connexons, which are embedded in the opposing gap junction membranes (1, 4, 7, 12, 13, 17) . The connexon is thought to be constructed from protein oligomers arranged in the form of an annulus and delineating a narrow hydrophilic channel through the membrane. The hydrophilic channel has been indicated repeatedly in various models of the gap junction, which is supposed to explain most of the available permeability data, obtained by fluorescence-labeled materials, showing that the channel allows a passage of small molecules up to 800-1200 daltons (11, 14). However, direct electron microscopic evidence showing the existence of a transversing channel has not been attained, although there have been reports indicating stain-penetrated cores of ca. 2 nm in diameter which appear to span the full 15 nm thickness of junctional membrane profiles in the negatively stained gap junction (5). However, alternative explanations of such images have been reported (8). We now report an electron microscopic study showing direct morphological evidence for the existence of a hydrophilic channel by using alkali-metal ions which pass through the channel physiologically. The experimental approach attempted here takes advantage of the fact that alkali-metal ions such as K+, Rb+ or Cs+ are accumulated in cells by the same osmotic pressure in that they replace each other in a mole for mole fashion under physiological conditions (9, 10), so that Cs+ or Rb+ serves as a physiological isotope for K+. In addition, Rb+ (an atomic weight of 85) and Cs+ (an atomic weight of 133) are heavy enough to be visualized by electron microscopy (3, 15). However, since the ultracytochemical demonstration of these water-soluble ions involves problems such as the difficulty of visualization and diffusibility of ions, we had to devise the following two techniques to resolve these

Direct visualization of the hydrophilic channel in the gap junction under an electron microscope using alkali-metal ions.