L7 Atypical CF Flashcards
What are the two types of cystic fibrosis
Classical and atypical
Stats regarding atpyical CF
Mild symptoms observed with only 1 or NO CFTR mutations
In Northern Europe - small incidence of two mutations and no symptoms
Upper airway cell model
APICAl
ENaC - Na absorption
CFTR - Cl secretion
Upper airway cell model
NKCC1
Na/K ATPase
K Channel - recycle K to allow function of NKCC1
What is the effect of increased Na absorption
Bring down the height of ASL - just in the CFTR mutants
Normal subunit composition of ENaC
abg(amma)
Where can mutations occur in ENaC
In all three o the mutants
How many ENaC mutations have been screened
45 different mutations
What is a common ENaC variant
A663 - no effect on function
What is an effect of the A663 mutation
This mutation predisposes to other mutations
How were the EnaC mutants screened
OE express a number of common ENaC mutations and record the amiloride sensitive Na current
What were the results of the ENaC mutant screening
Some - size of the current is exactly the same so unlikely this mutation is having any affect on function
Some there an increase in the function - could cause symptoms
Two there is a loss of function
- height of the ASL would increase
What is the activity of ENaC in classical CF - why is this
ENaC enhanced
No longer inhibition of ENaC
Where does the aW493R occur
In the effector loop of one of the subunits
Describe the trace seen for aW493R compared to the wildtype
When amiloride removed greater current seen in the mutant compared to the wildtype
In the aW493R mutant is there a difference on the T/A backgrounds
No effect on these results
What is Na feedback inhibition
As Na moves into the cells and [Na] increases
This promotes the endocytosis of ENaC from the membrane
What is the question asked regarding Na feedback inhibition
Is there a change in this in mutants
Does the mutations prevent the endocytosis of ENaC
Describe how the question of the mutations affecting Na feedback inhibition was adressed
Use ECF of low Na - Na still able to move in but endocytosis prevented
Does aW493R affect Na feedback inhibition
Comparing low and high Na
Decreased currents with high Na outside
This is also seen in the mutant
Percentage drop is similar low to high
Describe how else ENaC channel activity may be activated
Cleavage by proteases to increase the Po
Two classes of cleavage
Uncleaved
Cleaved
Describe the uncleaved channels
Near silent
Low Po
Generate smaller currents
Describe the cleaved channels
Very active
High Po
Generate larger currents