Gap junctions Flashcards
What are impermeable junctions called in invertebrates?
septate junctions
What are impermeable junctions called in vertebrates?
tight junctions
What is the role of a tight junction?
Allow active glucose transporters to absorb glucose from gut, passive transporters
export it to extracellular space/blood
What does current “rectifies” mean?
Current can flow either direction but favours one direction
What is a role of gap junctions between axons?
Gap junctions between neuronal axons are suggested to synchronize neuronal firing
How is the gap junction structure formed?
6 connexins form a hemichannel, connexon. Connexons are taken to the cell surface (via vesicles, via microtubules), connexons can then diffuse to cell-to-cell contact regions, and partner to a connexon from a neighbouring cell.
What do gap junctions do?
allow the exchange of ions, second messengers, and small metabolites between adjacent cells and are formed by two unrelated protein families, the pannexins and connexins
What is the size of the gap junction channel hole?
1.5 nm
allows RNA, small ions, peptides, sugars, vitamins
Which factors close gap junctions?
acid pH
high [Ca]i
What are some features of Pannexin channels?
may be opened by low [Ca]o, or ischaemia, releasing intracellular constituents like ATP, glutamate.
Which tissue contains high density of gap junctions?
liver
At the AV node are there many or few gap junctions?
few
slows propagation of impulse - allows unidirectional squeese
this can cause problems/prone to go wrong
What does it mean that gap junction connexons are promiscous?
bind to connexons across cell and species barriers
What role do gap junctions play in gut?
sychronisation of peristalsis
What is the effect of low [Ca]o on gjs?
likely to open (promoted conformational change –> twisting open)
What is an example of metabolic cooperation through gap junctions?
mutant cell lacking thymidine kinase
- no silver
normal cell with thymidine kinase containing silver grains can pass phosphorylated thymidine to mutant cell through gap junction
Why are gap junctions important in lens/cornea?
No blood vessels to pass nutrients
in cataracts opacity of lens due to failure of metabolic cooperation
Does low ph open or close gap junctions?
closes gap junctions
How might ca affect gene expression in development?
Ca rise activates ATP release → P2X, P2Y rs raise [ca] more
The rise of [Ca] may fall with distance, giving a mechanism for differential gene expression according to location – could be relevant to specifying positional information in development
