List of abbreviations
of micros-
specialist terms
explained in
English +

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

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Dr. med.
H. Jastrow

of use
Overview Gap-junction (Nexus, Macula communicans):
Pages with explanations are linked to the text below the images if available! (Labelling is in German)
An entire English version of this page is in preparation!
gap-junction = Nexus between 2 pilar
cells of the cochlea (guinea pig)
stereo image of a nexus, pilar cells
(guinea pig)
stereo image of a nexus, pilar cells
(guinea pig) 2
nexus in intercalated disc
heart muscle (monkey)
heart mucle: intercaltaed
disc overview (monkey)
detail: nexus and fascia
adhaerens (monkey)
Nexus in intercalated disc
of heart muscle (rat)
gap-junction heart
muscle cell (rat)
gap-junction detail from 
intercalated disk (rat)
Gap-Junction, eye
lens epithelial cells (rat)

A nexus or gap junction is an electrical synapse (nonvesicular synapse; Terminologia histologica: Macula communicans, Nexus, Synapsis non vesicularis, Synapsis electrica). It consists of spot- or stripe-like communicating junctions (Terminologia histologica: Junctiones communicantes) between two neighbouring cells. Nexus are well formed in the intercalated discs of heart muscle cells and here are arragned as round to irregular cell-cell contact areas with a contact surface of up to 1 µm². Otherwise this kind of cell-cell contact shows diameters of 0,1 1 µm whereby the distance between the cell membranes involved is only 2 - 3, maximal 5 nm. In the nexus tunnel proteins (connexons) of the cell membranes of adjacent cells directly continue into each other.

molecular composition:
The connecting tunnels are formed by an exact aggregation of two open pores of the cell membrane of neighbouring cells (1 per cell) which as hlaf-channels are called connexons (Terminologia histologica: Connexonae). One connexon consists of 6 subunits
of the protein connexin (Terminologia histologica: Connexina) in hexagonal arrangement in each cell membrane. Thus a complete tunnel consists of 2 x 6 = 12 connexin molecules. Seventeen different genes are known to code for connexins. In some cases even different kinds of connexins are present in the same nexus. Connexin 43 (molecular weight: 43.000 Da) is typical for the nexus of heart mucles cells, vascular endothelial cells and astrocytes. The nexus of basal cells of the skin consist of connexin 43, the epithelial cells of the above stratum spinosum of connexin 31 (molecular weight: 31.000 Da). Connexin 32 (32.000 Da) and connexin 26 (26.000 Da) are present in nexus between epithelial cells of pancreas, liver and gut. The cell membranes of  Schmidt-Lanterman's incisures of peripheral nerves contain gap junctions with connexin 32. Under normal conditions small molecules and ions can penetrate the myelin sheath here easily.

Function is is only available in the professional version of this atlas.

--> cell-to-cell contacts, tight-junction, desmosome, fascia adhaerens, synapse
--> Electron microscopic atlas Overview
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Three images were kindly provided by Prof. H. Wartenberg; other images, page & copyright H. Jastrow.