Lecture 23 Flashcards
Where is vasopressin produced?
in the hypothalamus
Where is vasopressin stored and released from?
The posterior pituitary gland
Where does vasopressin bind and to which receptor?
It binds to the vasopressin receptor (V2) on the basolateral membrane of LDT and CD cells
What is the effect of vasopressin binding to its receptor on the cells of the LDT and CD?
Results in incorporation of AQP2 channels
into the apical membrane = increase H2O flow
How long does it take AQP2 to appear in the apical membrane of cells of the LDT and CD after vasopressin binds to the V2 receptor?
30-40mins
What are the osmoreceptors that detect the changes?
The osmoreceptors in the hypothalamus stimulate the process of the ADH release. Macula densa cells in the thick ascending limb monitor Na+ to control H2O balance
What happens when vasopressin binds to its V2 receptor?
The GPCR activates adenylate cyclase which converts ATP to cAMP which activates PKA and this initiates the movement of vesicles out to the membrane
What are 5 symptoms of diabetes insipidus?
- ________ - large volume - _________ urine(>15L/d)
- ________ - excessive __________
- First year of life - v________, f______, slow g________, developmental ________
- Severe ________
- Severe cases - mental _________ due to dehydration of the ______–
- Polyuria - large volume - hypotonic urine(>15L/d)
- Polydipsia - excessive drinking
- First year of life - vomiting, fever, slow growth, developmental delay
- Severe dehydration
- Severe cases - mental deficiency due to dehydration of the brain
What are the two types of diabetes insipidus?
Central/neurogenic diabetes insipidus
Nephrogenic diabetes insipidus
Describe CDI
this is due to a lack of production of vasopressin by the hypothalamus due to a problem with the supraoptic or paraventricular nuclei or release from the posterior pituitary gland
Describe NDI
This is a problem at the level of the kidney
What are the two types of NDI? What causes each of these?
- congenital X-linked NDI: due to a mutated V2
receptor which occurs in 90% of NDI patients (normally males) - autosomal NDI: due to mutated AQP2 channel which occurs in 10% of NDI patients (there is normal V2 function)
How many mutations in the V2 receptor can result in congenital NDI?
200
What mutations cause autosomal NDI
the mutations in the NPA boxes (aparagine-proline-alanine) or in the pore itself
Mutations of the V2 receptor can arise in a number of different ways:
• non-functional ________ channels and _______ receptors
• ineffective ________ of _________ (AQP2 or V2)
• simple binding _________ of V2 receptors
• intracellular _________ problems (AQP2 or V2)
• accelerated ________ of AQP2 channel or V2 receptor to the _________ or ___________
- non-functional AQP2 channels and V2 receptors
- ineffective biosynthesis of protein (AQP2 or V2)
- simple binding impairment of V2 receptors
- intracellular trafficking problems (AQP2 or V2)
- accelerated degradation of AQP2 channel or V2 receptor to the proteasome or lysosome
Which of the following statements is TRUE?
A. Vasopressin is produced in the supraoptic and
paraventricular nuclei of the posterior pituitary gland.
B. Central diabetes insipidus is a problem with vasopressin production, storage and release from the hypothalamus
C. Nephrogenic diabetes insipidus (NDI) is a problem at the level of the late distal tubule and collecting duct.
D. Individuals with NDI exhibit reduced urine production.
C. Nephrogenic diabetes insipidus (NDI) is a problem at the level of the late distal tubule and collecting duct.
What is Bartter’s syndrome? What are the symptoms?
An autosomal recessive disorder that results from a problem with the transport proteins of the epithelial cells of the Thick Ascending Limb. This causes salt wasting, hypereninism and hyperaldosteronism, metabolic alkalosis, hypokalemia
Why does Bartter’s syndrome result in hypereninism and hyperalsosteronism?
Because the macula densa cells monitoring the Na+ in the filtrate detects high Na+ in the filtrate so releases aldosterone and renin
How many different types of Bartter’s syndrome are there?
3
What causes the three different types of Bartter’s syndrome?
In the thick ascending limb of the loop of Henle:
- mutation in the NKCC2 in the apical membrane causes Bartter’s syndrome type 1
- a mutation in the ROMK1 channel in the apical membrane causes Bartter’s syndrome type 2
- a mutation in the Cl- channel CLCNKB in the basolateral membrane results in Bartter’s syndrome type 3
How does type 1 Bartter’s syndrome affect the movement of Na+, Mg2+ and Ca2+?
When the NKCC2 channel is impaired, this affects the overall function of the transporter which affects the charge separation across the membrane and this affects the transport of Mg2+, Na+, Ca2+
What mutation causes Bartter’s syndrome type 2?
Y60X mutation in ROMK1
How does Bartter’s syndrome type 2 affect the movement of Na+?
If K+ can’t leave the apical membrane due to a mutation in the ROMK1 channel, K+ won’t enter via the NKCC2 channel and therefore Na+ won’t come in either
How does Bartter’s syndrome type three affect the movement of Na+?
If Cl- can’t leave the basolateral membrane due to a mutation in the CLCNKB channel, Cl- won’t enter via the NKCC2 channel and therefore Na+ won’t come in either
The loss of Na+ in the thick ascending limb as a result of Barter’s syndrome means what for the reabsorption in later parts of the nephron? What symptoms does this cause?
The reabsorption in the late distal tubules and collecting duct cells increases which can result in metabolic alkalosis and hypokalemia
Mutations of NKCC2, ROMK1 and CLCNKB mean what happens?
• non-functional _______ or ___________
• ineffective _________ of ___________
• simple binding __________ of __________
• intracellular _________ problems
• accelerated _________ of the ________ or _________
- non-functional channels or co-transporters
- ineffective biosynthesis of protein
- simple binding impairment of NKCC2
- intracellular trafficking problems
- accelerated degradation of the channels or co-transporters
Multiple choice question on Bartter’s Syndrome
Which of the following statements is TRUE?
A. Bartter’s Syndrome Type 3 (BS3) is a problem with the
Distal tubule.
B. BS patients exhibit hyporeninism and hypoaldosteronism.
C. BS1 patients have a mutations of the Na-K-2Cl cotransporter.
D. BS3 patients exhibit hyperkalemia.
C. BS1 patients have a mutations of the Na-K-2Cl cotransporter.
Where does Liddle’s syndrome occur?
In the late distal tubule and the collecting duct
What are four symptoms of Liddle’s syndrome?
- ______ due to increased _______ reabsorption
- ________ metabolic _______
- __________
- suppressed levels of _______ and ______
- hypertension due to increased Na+ reabsorption
- hypokalemic metabolic alkalosis
- pseudoaldosteronism
- suppressed levels of aldosterone and renin
What normally occurs in the collecting duct principle cell?
Na+ is reabsorbed and K+ is secreted under the influence of aldosterone
What normally occurs in the collecting duct intercalated cells?
K+ reabsorption
What happens to the collecting duct principal cells during Liddle’s syndrome?
There is an increase in Na+ reabsorption via ENaC because the channels are retained in the membrane so there is an even greater change in membrane potential which increases the amount of K+ loss which leads to hypokalemia. There is also an increase in pump function which will mean more K+ is entering the cell (basolaterall) in exchange for Na+ so more K+ leaves.
What is the purpose of the intercalated cells of the collecting duct?
pH balance
What happens to the collecting duct intercalated cells during Liddle’s syndrome?
The increased luminal negative voltage causes H+ secretion and HCO3- recycling by the intercalated cells
Hence, metabolic alkalosis (increase H+ loss and gain of HCO3-)
There is hypokalemia and metabolic alkalosis in both Liddle’s syndrome and Bartter’s syndrome
true
Why is there increased Na+ reabsorption in the collecting duct in patients with Liddle’s syndrome?
ENaC:
a, b, g subunits to make a functional channel
• PY motifs on C-termini- protein-protein interactions
• Normally, Nedd-4-2 leads to an increase ubiquitylation of ENaC; which tags ENaC to be removed from the apical membrane and targeted for degradation
In Liddle’s syndrome, there are mutations of the β (R566X) and γ so there is no C-terminus so the channel can’t be tagged to be taken out of the cell
Which of the following statements is FALSE?
A. Liddle’s Syndrome patients have hypokalemia.
B. The number of ENaC channels at the apical membrane are increased in patients who have Liddle’s Syndrome.
C. In Liddle’s Syndrome, patients have hyperaldosteronism.
D. The R556X mutation of ENaC results in too many ENaC channels at the apical membrane of cells of the Collecting Duct.
C. In Liddle’s Syndrome, patients have hyperaldosteronism.
