Gap junctions: consist of a single type of protein
subunit, connexin
A single junction consists of two apposed hexagonal rings
of connexins, called connexons, one from each of the
adjoining plasma membranes.
Channels are 16-20 Å in diameter: only molecules of
< 1000 D can pass through
Channel diameter varies with [Ca 2+]: open when
concentration is < 10-7 M, narrow and close when > 5 x 10-5 M;
protects other cells from cell death
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