Lecture 7

Question 1

What are the features of Atypical CF?

Answer 1

• Mild symptoms
• 1 or NO CFTR mutations
• 1-2% Northern Europe 2 mutations NOT observed
• Modifier genes – genes that code for proteins that regulate CFTR, or regulate expression of CFTR, help it to function normally

Question 2

What is the hypothesis for ENaC mutations in the airway?

Answer 2

• These are gain of function mutations
• More Na+ absorbed
• Depletion ASL (PCL)
• CF like symptoms

Question 3

Classical CF - nasal potential differences?

Answer 3

 More neg transepithelial potential
 CFTR mutated – no Cl secretion
 Enhanced ENaC

Question 4

ENaC mutation plus 1 CFTR mutation

Answer 4

 50% normal CFTR
 Quite normal Cl secretion/ CFTR function
 Enhanced response to amiloride

Question 5

Mild CFTR polymorphism

Answer 5

 High cl secretion – close to normal

 Enhanced response to amiloride – depletion of Na from the ASL – height decreases

Question 6

What are the features of W493R mutation?

Answer 6

• Found on EC loop of subunit
• increased ENaC currents
• ENaC currents massively enhanced
• Doesn’t matter which background you have
• Could be due to open probability (or number of channels

Question 7

What are the features of Na feedback inhibition?

Answer 7

• Promotes the endocytosis of ENaC from the membrane
• Way to look – activate channel but with low EC Na+
o Less going in – low IC Na+ - don’t stimulate endocytosis
o Mutant = less endocytosis
• If this doesn’t work – end number higher
1. ENaC opens – Na+ floods into the cell
2. IC Na+ increases
3. ENaC retrieved from the membrane
4. Feedback inhibition prevented by low EC Na+

Question 8

what is the effect of alphaW493R on amiloride currents?

Answer 8

• Bigger currents in mutant – involves channel opening

* Percentage drop in both is v similar

Question 9

What are the features of uncleaved channels?

Answer 9

o Near silent
o Low Po
o Generate smaller ENaC currents

Question 10

What are the features of cleaved channels?

Answer 10

o Very active
o High Po
o Generate larger ENaC currents

Question 11

what is alphaW493R response to chymotrypsin?

Answer 11

o In absence of chymotrypsin – open probability v high
o No activation of near silent channels.
o Reduced response to chymotrypsin not due to increased endogenous cleavage before chymotrypsin added.
o Mutation in ENaC made channels resistant to cleavage – but open probability still high

Question 12

What is the effect of the mutation on Na self inhibition?

Answer 12

o Increase in currents but no Na self-inhibition

o Currents stay big

Question 13

what was the effect of the betaV348M mutation on open probability?

Answer 13

measured amiloride sensitive whole cell currents
open probability increased
enhanced ENaC function
no change in channel number

Question 14

what is MTSET used for?

Answer 14

• MTSET used – sulfhydryl agent, binds to cysteine, stabilises open state of channel – keeps in open configuration

Question 15

what is the effect of overexpressing SCNN1b in mice?

Answer 15

•	Mutant - Height is reduced – cilia bent – seen in classical CF 
o	Reduced PCLheight 
o	Poor mucus clearance in model 
•	Enhanced ENaC function
o	Mimics wants seen in CF patients

Question 16

What mutations cause all forms of CF?

Answer 16

• Loss of function CFTR
• Loss of function ENaC
• Gain of function ENac
• NOT gain of function CFTR

Question 17

what is the effect of SCNN1b on mortality?

Answer 17

• By 28 days after birth less than 50% of animals remaining

Question 18

what is the effect of SCNN1b on the lungs?

Answer 18

• Lungs congested – lots of mucous plaques and plugs

o Increased thickness of mucous