week 19 epithelial fluid secretion Flashcards
which has a greater fluid recover volume? small or large intestine
small 7L
Large 1.9L
what disease inhibits fluid reabsorption in the gut?
cholera
ion movement across a ‘tight’ epithelial monolayers drives _____ movement
water
polarised organisation of channels, pumps, exchangers and junction proteins determines _____ and ______ of water movement
direction and movement
how many routes of transepithelial water movement are there
2
intracellular movement of water occurs where
inside cells
intracellular movement of water occurs within cells and is regulated by what
water channels - aquaporins
paracellular movement of water occurs where
between cells
paracellular movement of water occurs between cells and is regulated by what
tight junction permeability
what are the 2 routes of transepithelial water movement
intracellular
paracellular
ENaC draws fluid from where of the cell nd into the blood
apical surface of the cell
what pump allows Cl- ions into the cell
NKCC
where is the NKCC pump located
on the basolateral surface of the cell
cl- accumulates in the ____ of the cell and creates ________ movement of which ion
lumen
paracellular movement
Na
Cl- channels = fluid _______
secretion
Cl- channels transport from where to where
basolateral to apical transport
Na+ channels = fluid _____
absorption
Na+ channels transport from where to where
apical to basolateral transport
what is the swelling-activated Cl- channel
(IClvol)
what does the swelling-activated Cl- channel (IClvol) do
how is it activated
activated transiently by osmotic shock
sustained opening does not occur
what is the calcium activated Cl- channel
CaCC
what does the Calcium activated Cl- channel do (CaCC)
how is it activated and is it transient?
activated by release of intracellular Ca2+ stores. Activity is transient and therefore unlikely to be sustained in development
what is the outwardly rectifying Cl- channel
(ORCC)
what does the Outwardly rectifying Cl- channel (ORCC) do
how is it regulated
regulated by release of intracellular ATP. Maintains potential by regulated depolarisation to physiological set point
what is the cystic fibrosis transmembrane conductance regulator
CFTR
what does the cystic fibrosis transmembrane conductance regulator do
what does it regulate and where
best characterised channel due to role in cystic fibrosis disease. Long presumed to be channel regulating fluid secretion in adult lung
what is the voltage dependant Cl- channel
CLCN
what does the voltage dependant Cl- channels (CLCN) do
where is it and what process development does it follow (organ)
recently characterised in lung. Expression pattern follows the process of lung development
what is the CFTR a member of
member of the ATP binding cassette (ABS) glycoprotein superfamily
what is the kDa of CFTR
170kDa
how many _ transmembrane domains is CFTR composed of
2x 6 transmembrane domains
how many nucleotide binding domains does CFTR have
2
what are the 2 nucleotide binding domains that CFTR has (common to all ABC proteins)
NBD1 and NBD2
how many R domains are there in CFTR
1
what is a unique feature of CFTR
has one single domain of highly charged amino acids
in CFTR, the R domain is a regulatory site containing several ______ sites for what protein kinases
phosphorylation sites
protein kinases A and C
activation of CGTR Cl- conductance requires ___ binding to what domains
ATP binding
to the NBD domains and phosphorylation of the R domain
how many stages are there in the normal cycle of regulation of CFTR
6
STAGE 1 of normal cycle of regulation of CFTR
what state is the channel in
channel is inactive
STAGE 2 of normal cycle of regulation of CFTR
what does cAMP activate
cAMP activation of protein kinase A phosphorylates R domain
STAGE 3 of normal cycle of regulation of CFTR
What does ATP bind to
ATP binds to NBD1 and NBD2
STAGE 4 of normal cycle of regulation of CFTR
what is hydrolysed
ATP is hydrolysed
STAGE 5 of normal cycle of regulation of CFTR
what happens to the channel
what ion is conducted
channel opens and conducts Cl-
STAGE 6 of normal cycle of regulation of CFTR
what happens to the R domain and subsequently the channel
dephosphorylation of the R domain inactivates the channel
what mutation in the NBD1 region of CFTR causes cystic fibrosis
Phenylalanine 508 (deltaF508 or F508del)
in delta508 CFTR (mutation that causes cystic fibrosis) what occurs
no fluid in the airway secretion
- dry lung
- sticky mucus
- pathogen colonisation
In CLCN1-7 what is the channel opening gated by
membrane potential
IN CLCN1-7 where is it found
epithelia
muscle
nerve tissue
plants
CLCN2 expressed in epithelium is activated at ______ cell membrane potentials
negative (hyperpolarised)
in CLCN 1-7 is composed of how many transmembrane domains
10
in CLCN1-7 the 10 transmembrane domains dimerise to form how many pores
2
in CLCN 1-7 the 10 transmembrane domains dimerise to form 2 pores, each pore is ________
voltage gated
CLCN1 mutation causes what
myotonia
in the CLCN1 mutation causing Myotonia - what does this cause
failure of muscles to relax after contraction as cells remain depolarised
what does a mutation in the CLCN5 mutation cause
Dent’s disease
in the CLCN5 mutation causing dent’s disease - what does this cause
fluid transport problems in kidney resulting in kidney stones, calcium and protein loss in urine
CLCN2 and CLCN3 are developmentally expressed in what foetal organ
lung
CLCN2 and CLCN3 are developmentally expressed in the feotal lung and control what
control lung fluid volume during development
where is the ENaC channel always found within epithelia
secretory epithelia
lung, kidney gut, salivary duct, sweat duct
how many subunits is the ENaC composed of
3
what are the 3 subunits ENac composed of
alpha
beta
gamma
in ENaC a genetic alpha knockout results in what
lethal at birth due to flooding of the lungs
in ENaC knockout of beta or gamma subunits results in what
not lethal but is associated with a marked reduction in the rate of Na+ transport
in ENaC what is the dominant pore forming subunit
alphaENaC
ENaC is composed of alpha, beta, and gamma but how many subunits are there
4
2 alpha subunits
In ENaC what is the extracellular loop rich in
cystine
In ENaC within the extracellular loop what type of tertiary structure is it rich in
CSSC sulphur cross linking
what residue is involved in channel opening and closing within ENaC
histidine glycine residue
in ENaC what residue rich region serves as a binding motif for NEDD4
proline tyrosine
proline tyrosine residue rich region which srves as a binding motif for what
NEDD4
proline tyrosine residue rich region which srves as a binding motif for NEDD4 is what kind of ligase
ubiquitin ligase
proline tyrosine residue rich region which serves as a binding motif for NEDD4, a ubiquitin ligase which targets the subunit for membrane removal and what kind of degradation
proteolytic
what is ENaC inhibited by
amiloride
What is ENaC activated by
Beta2 adrenergic agonist
ENaC conductance is induced by what
catecholamines
pseudohypoalosteronism (PHA) and Liddle’s syndrome are diseases associated with loss and gain of function mutations on what channel subunits
ENaC
PHA disease is associated with resistance to what hormone
aldosterone
As PHA is a disease associated with resistance to aldosterone what ion imbalance does this lead to
increased Na excretion
- dehydration
- hypotension
-hyperkalaemia
- metabolic acidosis
PHA disease is most evident in what organ
kidney
most lethal form of PHA is caused by loss of funtion mutations in what subunit in ENaC
alpha
beta
gamma
Liddle’s syndrome is charcterised by what
hypertension
hypokalaemia
metabolic alkalosis
repressed aldosterone secretion
results from gain of function mutations on what terminus domain if beta and gamma subunit in ENac
C terminal domain
In liddle’s syndrone
results from gain of function mutations in the C terminal domain of beta or gamma ENaC which result in the deletion of how many amino acids in the proline tyrosine rich PY domain
45-75 amino acids
results from gain of function mutations in the C terminal domain of beta or gamma ENaC which result in the deletion of how many amino acids in the deletion of 45-75 amino acids from what domain
proline-tyrosine rich PY domain
what ubiquitin ligase promotes internalisation and degradation of PY motif
NEDD4
channel activating proteases (CAP) increase what activity
ENaC
what increases ENaC activity
Channel Activating Proteases (CAP)
secreted CAP inhibitors block what and in what
secreted CAP inhibitors block CAP activity in concentrated ASL
how many extracellular CAPD are found in ASL
3
three extracellular CAPS dound in ASL can cleave what
ENaC
three extracellular CAPS found in ASL can cleave ENaC does what to its activity
increases the activity of ENaC
High ASL dilutes secreted what and secreted what
dilutes secreted protease inhibtors
dilutes secreted CFTR agonists
Low ASL concentrates secreted CAP protease inhibitors and secreted _____ agonists
CFTR
