Molecular physiology of salt reabsorption- part 2 Flashcards
What is the ASL?
Airways surface liquid
covers the epithelial cells
subdivided into the true liquid layer and a mucus layer
includes the PCL and mucus layer
What’s the physiological problem with the ASL?
As you move up the respiratory tract- structures become larger and the SA decreases
This means the ASL increase in height as you go up, due to the SA decreasing but the volume load remaining the same
=having a too high ASL- problem- impacts the ability to clear mucus
What are the two proposed mechanisms of how the ASL height is controlled?
Passive mechanism
Active mechanism
What was the study that involved cultured human airway epithelial cells?
They added fluid to the top of the cells (height reached 30 microns)
saw that the height dropped over time until it reached the optimum height (7 microns)
Wanted to see what was controlling this change in height
What did they see in terms of % inhibition of Vte when they added amiloride and bumetanide?
As the ASL layer dropped, the Vte fell from 14mv to 5-6mv
Over 48 hours the amount of amiloride-sensitive current inhibition of the Vte dropped- aka the amount of sodium absorption dropped (the blocker was having less of an affect)
Over 48 hours the amount of bumetanide-sensitive current inhibition of the Vte increased- aka the amount of chloride secretion increased
What does the cell model look like for upper respiratory tract cell?
Enac channel in apical membrane
CFTR channel in apical membrane
NA/K ATPase in basolateral membrane
Na-K-2Cl co -transporter in basolateral membrane
Potassium channel in basolateral membrane
What is RSV and what are its symptoms?
Respiratory syncytial virus nasal congestion runny nose bronchiolitis in children can lead to pneumonia in adults
How does RSV affect Enac?
Inhibits ENac function
highlighted by the drop in amiloride-sensitive current when RSV is added to mouse tracheal cells
How did they establish if glycoproteins were to blame for the Enac inhibition?
Add RSV and NA (an inhibitor of glycoproteins) to tracheal cells and measure the amiloride-sensitive current
Saw a fall in AMC
Clearly not glycoproteins inhibiting ENac
How did they establish if PKC was to blame for the inhibition of Enac?
Add RSV and BIM (PKC inhibitor) to the tracheal cells and measure the amiloride-sensitive current
No change in the AMC
Tells us that downstream of the virus is the activation of PKC
How did they establish if glycolipids were to blame for ENac inhibition?
Add RSV and PPMP (inhibitor of glycolipids) to M1 cells and measure the AMC
Saw the restoration of the AMC
The virus is binding to glycolipids- which is then stimulating pathways including PKC- downstream effect is inhibiting the epithelial sodium channels
What proteins are found on the influenza virion?
The virion contains main glycoproteins-
matrix protein M1
haemoggluttin
M2- acid activated proton channel
What does the overexpression of M2 in airway cells result in?
Reduced ENac currents
- impacts on the open probability of the channels
- they open but not for long
- western blot data- less enac- alpha and beta- expressed
What is M2 doing to ENac channels to inhibit them?
Triggering their endocytosis
In liddle’s version of ENac- these channels arent affected by M2- they cant be endocytosed
How is ROS also involved in Enac inhibition?
Via immunostaining
Where M2 is overexpressed- areas of ROS
