what is the incidence of cystic fibrosis?
- 1 in 2000/2500 live births
- 1 in 20 are carriers
- most common lethal genetic disease in caucasians
give some features of CF
- exocrine pancreas insufficiency - digestive issues
- increase in sweat [Cl]
- male infertility in 95% (vas deferens fails to form)
- increased risk of developing airway disease/infection - unsufficient lung functionality/ tissue to support life
Why is there a higher risk of airway infection in CF patients?
- reduced function of CFTR - less Cl- secretion, and less water movement into the lumen
- Lower height of liquid layer
- cilia bent over - cannot beat effectively due to low height of PCL - cannot clear mucous/bacteria from lungs/airway effectively
what was the shark rectal gland a good model for?
- first important model for Cl- secretion - secretes large amounts of Cl- and is a robust tissue (unlike mammalian tissue)
- leaky epithelia - secretes large amounts of NaCl
what channels are on the basolateral membrane of the shark rectal gland cells?
Na/KATPase - Na out of cell, K into cell
NKCC1 - Na, 2Cl and K into the cell
K+ channel - out of cell
what does barium block in shark rectal gland tissue and what are the consequences of this?
- barium blocks K+ channel - the membrane depolarises more towards 0 - less driving force for Na movement as a decrease in NKCC1, this causes a decrease in Cl- secretio
what does ouabain block and what are the consequences of this?
Ouabain blocks Na/K+ ATPase - IC Na+ increases, therefore driving force for NKCC1 is less and this reduces the function of NKCC1 and other proteins which rely on a Na+ gradient
- less Cl- comes into the cell
- less Cl- available for secretion - less Cl- secretion
what does furosemide block?
furosemide (or bumetanide) blocks NKCC1
- block Cl- influx via the basolateral membrane, less Cl- available for secretion - reduction in Cl- secretion
what does Cl- secretion depend on?
depends on amount of K+ and Na+ in perfusate - determines driving for for Na+ and K+ movement
What happens is K+ or Na+ is removed from the perfusate?
If Na+ or K+ is removed form the perfusate Cl- secretion is inhibited
what basolateral channels/models are applicable to most cl- secreting epithelia?
- NA/K ATPase
- NKCC1
- K+ secreting channel
what is meant by electrochemical equilibrium in terms of Cl-?
- If there is am accumulation of Cl- in the cells, but then Cl- channels open - the cell drops to electrochemical equilibrium - no excess Cl- in the cell - just going straight out
what should [Cl-] be if it is passively distributed in the cell? What was shown in shark rectal gland?
- if passively distributed, [Cl-] should be between 17-28mM
- But was 70mM - shows [Cl-] is above electrochemical equilibrium - ACCUMULATING to a higher conc in cell then what is expected
what is accumulation of Cl- in cell above electrochemical equilibrium due to?
- due to active transport by Na/K ATPase - use energy to set up Na gradient for NKCC1 to bring Na/K/Cl into the cell - causes Cl- accumulation
( is not passive)
what can bring cl- to equilibrium?
Use of furosemide - inhibits NKCC1 - brings Cl- to equilibrium - stops accumulation of Cl- into the cell
what does cAMP stimulate?
stimulates CFTR and Cl- secretion across the apical membrane
How can distal obstructive syndrome be caused?
By no or inactive CFTR - less Cl-secretion - less water movement into lumen
what can be caused by overactive CFTR?
Overactive CFTR - more Cl- secretion, more water secretion into the lumen
what cells in the colon secrete Cl- via CFTR?
lower to mid crypt cells
how can Cl- secretion be stimulated?
Cl- secretion can be stimulated by Ach or prostaglandins (e.g. PGE2)- increase Ca2+ or cAMP
what happens to colon cells when Ach applied?
Ach increases the IC Ca2+ levels
- This activates Ca2+ activated K+ channels - drive K+ secretion
- this hyperpolarises the cell, and creates a driving force to NKCC1 to bring Na/K/Cl into the cell - drives more Cl- secretion
(NKCC1 causes Cl- accumulation into the cell)
give some features of the CFTR channel
- 12 TMD
- 2 NBDs (nucleotide binding domains) (bind nucleotide which regulates the opening and closing of the channel)
What is the delta F508 mutation?
- mutation - phenylalanine deletion in NBD1 (common mutaiton in CF, 70-90% of patients)
What is the G551D mutation?
in 13% of CF cases
- also in NBD1
- mutation - aa substitution (glycine to aspartic acid)
