Lab 4 - DNA analysis Flashcards
What type of epithelium is ENaC found in?
In the apical membrane of epithelial cells lining the late distal tubule and collecting duct regions of the kidney nephron
What is the function of ENaC in kidney?
When the body needs more sodium the ENaC are switched on and sodium is reabsorbed from the urine
What type of epithelium is ROMK1 found in?
In the apical membrane of both the kidney thick ascending limb epithelial cells and principle cells of the collecting duct.
What is the function of ROMK1 in the kidney?
Potassium ions flow through the ROMK1 channel so potassium its secreted from the epithelial cells into the developing urine.
What is the name given to changes in DNA sequence?
Mutation
What is Bartter’s syndrome?
Bartter syndrome is an autosomal recessive disorder of salt reabsorption resulting in extracellular fluid volume depletion with low/normal blood pressure.
Impairment in the sodium-potassium-chloride cotransporter (NKCC2), potassium channel (ROMK), or CLC-Kb channel affecting the transport of sodium, potassium, and chloride in the thick ascending limb of the loop of Henle (TALH). This results in increased distal delivery of these ions, where only some sodium is reabsorbed (decrease in Na+ reabsorption), and potassium is secreted (increase in K+ secretion).
What is Liddle’s syndrome?
Liddle syndrome is a rare cause of secondary hypertension due to a dominant genetic mutation affecting the function of the collecting tubule sodium channel (ENaC).
Is Bartter’s syndrome an autosomal recessive or dominant disorder?
Autosomal Recessive (requires two mutated ROMK1 alleles)
What are the symptoms of Bartter’s syndrome?
Hypokalemic, plasma pH more alkaline than normal and higher than normal aldosterone levels.
Constant fluid and electrolyte loss
many require kidney transport
What effect will changing tyrosine 60 to a stop codon have on the ROMK1 gene?
Stop codon occurs before the subunit - therefore nothing beyond that point gets transcribed - therefore get junk protein because does not containing necessary transmembrane protein that gives the function = NON function channel.
How do mutations in the proteins involved in the TAL cause Bartter’s syndrome?
Lower K+ in the lumen = reduced K+ for NKCC2 = slower NKCC2 activity = reduced Na+ reabsorption
Other than ROMK1, what other channels when mutated can cause Bartter’s syndrome?
Bartters type 1 = NKCC2 (prevents Na+ reabsorption)
Bartters type 3 = CLC-KB (Reduces Na+ reabsorption)
Why can a mutation to any of NKCC2, ROMK1, CLC-KB or Na/K-ATPase cause Bartter’s syndrome?
Mutation occurs on different genes
What are common symptoms of Liddle’s syndrome?
High BP, low aldosterone levels.
Is Liddle’s syndrome autosomal recessive or dominant?
Dominant (mutation in just one allele)
What is the effect on the beta ENaC protein when arginine 566 is changed to a stop codon?
Mutation (stop codon) occurs after the subunit therefore entire protein still transcribed so channel still functions. However the end terminal contains the PY motif required for ENaC endocytosis to remove the channel from the apical membrane.
Impaired degradation of ENaC meaning that channels stay in the membrane and cannot be removed. This leads to a greater number of channels and therefore greater reabsorption of Na+ into the cell.
What percentage of Na reabsorption occurs in the thick ascending limb?
25%
What percentage of Na reabsorption occurs in the principle cells of the collecting duct?
3%
What is hypoclemina?
Low potassium levels
What effect does Liddle’s syndrome have on homeostasis?
Increased ENaC
Increased Na+ reabsorption
Increase H20 reabsorption leading to increased plasma volume
Increase blood pressure (hypertension)
increased K+ secretion (hypokalemia)
