Enac Pathophysiology Flashcards
What is the ASL and what does it consist of? What is its main function?
Airway surface layer - consists of true liquid layer and the mucous layer. Interchangably called the PCL.
Main function is that it is the first line of defence against pathogens –> beats to remove microbes from the respiratory tract via motile cilia. it has an Optimum height for which to do this!
What is the problem with the ASL wrt surface area and the cilia?
As you move up the respiratory tract, structures get bigger and the surface area goes down. Means the volume load gets bigger as you move up the tract and there is more of a load for cilia to move
How does the ASL ACTIVELY control its height?
Via epithelial cells –> when the height is too low, salt ions are secreted - water follows causing the height to increase
When the height is too high, ions are reabsorbed, water follows and the height decreases
How does the ASL passively control its height?
The mucous layer behaves as a reservoir –> when too high, fluid moves into the mucous layer and cilia beat to remove from the respiratory tract
When the layer is too low, water moves out of the mucous layer and into the PCL, allowing maintenance of optimum height
Cultured human epithelial airway cells –> how did this experiment show that cells were activating processes to allow excess liquid to be reabsorbed?
Fluid was added to the cultured cells and the height of the ASL was monitored using a fluorescent indicator
After 24 hours the height of the layer dropped dramatically –> cells were therefore activating processes to allow excess liquid to be reabsorbed
Pharmacologial approach to investigating the ASL –> use of Amiloride ?
Measured the Tme across cultured cells upon addition of Amiloride and Bumetanide
- Normally caused a drop in the height of the ASL – by blocking Enac you are preventing reabsorption of Na+ and therefore by blocking Enac you are downregulating the reabsorption of Na+ and causing a reduction in Tme
Pharmacologial approach to investigating the ASL –> use of Bumetanide (blocker of Cl- secretion) ?
Less change in height of ASL seen –> at a steady state, more Cl- is secreted than Na+ reabsorbed.
At a high liquid layer height, more Na+ is being absorbed than Cl- secreted (hence less water reabsorbed and liquid layer higher!)
In the cell model, how is Cl- and Na+ controlled to change the height of the liquid layer?
NKCC1 on the basolateral membrane creates a gradient for the secretion of Cl- by creating high IC [Cl-] for when the layer is too low, as well as the recycling of K+ causing hyperpolarisation of the membrane which creates a driving force for the secretion of Cl-
Na+/K+ ATPase creates a low intracellular [Na+] as well as recycles K+ back out of the cell, creating a driving force for the reabsoprtion of Na+ (when layer is too high)
Respiratory Syncitial virus – symptoms of disease and general pathophysiology?
Causes nasal congestion, pneumonia in adults and bronchitis in children
What was shown using amiloride in mouse models of RSV?
Expose mice to virus, inject with amiloride –> a smaller shift in currents is seen in mice with virus
Amiloride is having less of an inhibitory effect therefore in presence of virus –> RSV is inhibiting ENac!!!!
How does RSV cause symptoms via ENac? Evidence?
Virus binds to glycolipids which stimulate signalling pathways via PKC –> this leads to the INHIBITION OF ENac
In trachea cells where virus present and PKC inhibitor, no impact to inhibitory currents is seen
What are the main, most relevant molecules of the influenza virus?
M1 - matrix protein
M2 - H+ channel inhibitor
Haemaglutin - activates PKC and therefore causes inhibition of ENac
What are the impacts of overexpressing influenza virus particle M2?
Impacts the Po of Enac by promoting its endocytosis from the membrane (this was shown by western blotting)
Increases the production of ROS which cause inhbition of ENac –> this can be reversed by the addition of antioxidants
ENAC L.O.F - PSEUDOHYPOALDOSTERONISM (PHA) in the kidney?
Loss of function in RENAL FORM –> AUTOSOMAL DOMINANT - loss of Na+ in urine, metabolic acidosis, high renin/aldesterone, salt wasting
ENAC L.O.F - PSEUDOHYPOALDOSTERONISM (PHA) in the systemic organs?
Loss of function in systemic sense –> AUTOSOMAL RECESSIVE - lower respiratory tract illness is seen! Higher liquid layer as Na+ is not being reabsorbed (so water follows), and salt in the mucus. Cilia cannot clear this high amount of mucus
