Pathophysiology of ENaC Flashcards
(39 cards)
The airway surface layer is divided in to
1) The true liquid layer
2) The mucous layer
What is the role of the mucous layer?
It is the first line of defence against respiratory pathogens
Describe the problem of volume load in the movement of ASL in the lungs
The alveoli have a large surface area, however this decreases up the lungs
This means we have the same amount of liquid over 50cm2 rather than 200cm2 up the respiratory tract
This means the height of the ASL would have to rise which would affect cilia movement if it is higher than the optimum and mucous would not be cleared effectively
Describe two ways it is thought that the ASL can be controlled
1) Passive - the mucous layer acts as a reservoir e.g. if the height of the liquid layer is too high then water will move in to the mucous layer
2) Active - Active ion transport where the concentration of salt is controlled in the liquid layer which subsequently controls how much water is in the liquid layer
Describe an in vitro experiment which shows the airway surface layer has an optimum height
Fluid was added to the top of cells (epithelia) so that the height was higher than the optimum (30ul)
The height of the layer went down over time to 7 ul where the height remained constant
What is the optimum height in vitro?
14 ul
What does amiloride block?
ENaC
What does bumetanide block?
NKCC1
What is the effect of bumetanide?
It blocks NKCC1 on the basolateral membrane which inhibits chloride secretion
Describe an in vitro experiment which shows the mechanisms involved in maintaining the optimum ASL height
Amiloride and Bumetanide was used and they looked at how much each blocked the Vte at time zero and at time 48 hours
e.g. on the graph bigger bar = bigger inhibition
Amiloride - at time zero amiloride gave 60% inhibition of the Vte which suggests lots of sodium is being reabsorbed so water follows = decrease in height
At 48 hours this had been down regulated
Bumetanide - at time zero only around 18% if the Vte was generated by chloride secretion but after 48 hours bumetanide inhibited around 50% of the Vte
Describe what the experiment with amiloride and bumetanide shows about the control of the ASL
When the ALS height is too high than Na+ reabsorption is greater than Cl- secretion
When the ALS height is too low then C;- secretion is greater than Na+ reabsorption
It also shows that the balance between the two is important for maintenance of the ASL height
Why is ENaC important at birth?
It is important for lung clearance at birth i.e. amniotic fluid needs to be cleared
Describe the cell model for the cells in the upper airway respiratory tract
Apical - ENaC, cilia and CFTR
Basolateral - Na+/K+ ATPase, NKCC1, potassium channel
1) K+ channel and ATPase set up the driving force for Na, 2Cl and K to move in to the cell through NKCC1
2) Na and K recycle = Cl accumulates
3) CFTR opens = cl secretion
What is RSV?
Respiratory syncitial virus
What are the symptoms of RSV?
Nasal congestion, bronchiolitis in children and pneumonia in adults
Major respiratory pathogen in children = 20% of hospital admissions
Describe the effect of RSV on short circuit current in mouse trachea
Mouse was exposed to RSV for an hour before amiloride was added
Before RSV exposure ENaC had a large function but after exposure this was smaller so it seems that RSV inhibits ENaC
So adding RSV reduced the short circuit current
RSV blocks ENaC so blocks Na+ reabsorption so there is excess fluid in the nose
How does RSV cause a runny nose?
RSV blocks ENaC so Na+ reabsorption is inhibited = more fluid is in the nose
What were the three possible mechanisms that RSV could work through?
PKC activation (ie inhibits ENaC)
Glycoproteins
Glycolipids
Which cell types were used to investigate RSV mechanisms to inhibit ENaC?
mouse trachea cells or principal cells
Does RSV work though PKC activation and what is the evidence?
Yes
SSC was measured with control conditions, with BIM (PKC inhibitor) or BIM and RSV
Hypothesis: if PKC is needed then when RSV is added with BIM, RSV will have no effect on the short circuit current
Results: There was no change in the SSC when BIM was added with RSV
So PKC is needed to be activated to inhibit ENaC
Does RSV work through glycoproteins and what is the evidence?
No
SSC was measured in control conditions with or without NA which inhibits binding to glycoproteins
Hypothesis: If glycoproteins are needed then adding RSV with NA will give no change in SSC
Results: When NA is added then the virus is still able to act through ENaC as SSC decreases
So Glycoproteins are not involved in a mechanism through which RSV inhibits ENaC
Does RSV work through glycolipids and what is the evidence?
Yes
SSC is meausured in control conditions or with PPMP which inhibits binding to glycolipids
Hypothesis: When glycoproteins are needed then adding PPMP with RSV will show no change in SSC
Results: PPMP and RSV = no change in SSC
So glycolipids are involved in ENaC inhibition through RSV
RSV works through which mechanisms?
PKC and glycolipids
Influenza works through which two mechanisms?
PKC and glycoproteins