Lecture 14 Flashcards
What are examples of substances reabsorbed via membrane carriers?
glucose, amino acids, via Na co-transporters
What is the renal threshold?
Not an absolute value, but in terms of ease of measurement, it gives an indication of level of amount of glucose in plasma where we start to see glucose in urine
What are the two systems included in the secretion by proximal tubule?
Organic cations
Organic anions
Is secretion by proximal tubule fast or slow?
Rapid
What are foreign compounds involved in the secretion by proximal tubule?
Penicillin
- therapeutic effect
- penicillin was being effectively cleared
- oral dose must be slightly higher to compensate
chemotherapy agents
- effectively cleared
- makes cancer treatment difficult
What does the Loop of Henle do?
Concentration of the urine
Reabsorption of Na, Cl and H2O
Reabsorption of Ca, Mg
Site of action of loop diuretics
What is the loop structure composed of?
Thin descending limb - reabsorbs H2O
Thin ascending limb - reabsorbs Na, Cl
Thick ascending limb - reabsorbs Na, Cl
What does the reabsorption of NaCl allow?
Control of concentration of urine
What is found in the apical membrane of the thin ascending limb?
NKCC2, ROMK (Kir 1.1)
What is found in the basolateral membrane of the thin ascending limb?
Na/K ATPase
CLCK
Barttin
What does NKCC2 do?
Net Cl reabsorption
Recycling of K is transporting sufficient K back into the extracellular fluid
What is ROMK involved in?
Rat Outer Medullary Potassium Channel
- transporting K out of thin ascending limb into extracellular fluid
What is CLCK?
Family of Cl channel
“K” for kidney
Regulated by Barttin
What is barttin?
Beta-subunit
Accessory protein that allows CLCK to function normally
What happens when Na and Cl are reabsorbed?
More Ca and Mg reabsorbed via paracellular pathway
How is Bartter’s syndrome inherited?
Autosomal recessive
What are the main symptoms of Bartter’s syndrome?
Salt wasting and polyuria Hypotension Hypokalaemia Metabolic alkalosis Hypercalciuria Nephrocalcinosis
Why does Bartter’s syndrome lead to salt wasting and polyuria?
Lose NaCl is urine
Increase in urine flow rate from not reabsorbing as much salt
Not necessarily happen in same part of nephron
Why does Bartter’s syndrome lead to hypotension?
Reduction in extracellular fluid volume
Low blood pressure
What is hypokalaemia?
Low plasma K (secondary effect of Bartter’s syndrome)
Secrete too much K in urine
What is metabolic alkalosis?
Not caused by a problem of the lungs but the kidney
Secrete too much H
What is hypercalciuria?
High levels of Ca in urine
At risk of kidney stone formation
What is nephrocalcinosis?
Formation of kidney stones
leads to Blockage in tubules
leads to Kidney damage
What genetic mutations can lead to Bartter’s syndrome?
Loss of function mutations in transporter proteins:
- NKCC2: no reabsorption of NaCl
- ROMK: Stops recycling of K across apical membrane
- stops NKCC2
- insufficient K to keep NKCC2 from transporting NaCl - CLCK: Cl can’t leave cell
- Cl accumulates
- stops NKCC2
- Level of Cl is too high
- Inhibit NaCl reabsorption - Barttin: CLCK doesn’t work
- same effect as CLCK inhibition
- subset of patients analyzed did not have mutations in proteins except Barttin protein gene
What is Fractional excretion?
Amount in urine/amount filtered
What is Fractional excretion of NaCl in ROMK knockout mouse?
Prevents K recycling
- similar phenotype as Bartter’s syndrome
What do the difference in fractional excretion suggest when compared to wildtype mouse?
Tubular defect 100% = all filtered excreted < 100% = some reabsorbed > 100% = some secreted - reduced ability of reabsorbing NaCl
What are symptoms found in ROMK knockout mouse that are NOT found in human Bartter’s syndrome patients?
Metabolic acidosis occurs NOT ALKALOSIS
Plasma K doesn’t change much
What do loop diuretics do?
Increase urine flow rate Treats hypotension Work at the level of Loop of Henle - Furosemide (Frusemide) - Bumetanide Block NKCC2 - block salt reabsorption - blocks water reabsorption If the dosage isn't right, it can lead to Bartter's syndrome like symptoms so optimum dosage is required
What is the Early Distal Tubule’s main function?
Reabsorption of Na and Cl
Reabsorption of Mg
What is the Early Distal Tubule sensitive to?
Thiazide diuretics
What does the Early Distal Tubule closely resemble?
Thick ascending limb
What is found in the apical membrane of the early distal tubule?
NCC
Mg transporter
What is found in the basolateral membrane of the early distal tubule?
Na/K ATPase
CLCK
Barttin
What does the part model of the early distal tubule show?
Low intracellular Na concentration
Doesn’t need K in the NCC
ATPase reabsorbs K
Net reabsorption of Cl
Mg permeable channel (Trp family of cation channels)
- Mg leaves cell but not much is known about it
- net reabsorption of Mg
How is Gitelman’s syndrome inherited?
Autosomal recessive
Are there more Bartter’s syndrome patients or Gitelman’s syndrome patients?
Bartter’s
What are the main symptoms of Gitelman’s syndrome?
Salt wasting and polyuria Hypotension Hypokalaemia Metabolic alkalosis Hypocalciuria - calcium defect is different (hyper vs hypo) - lower amounts of Ca in urine Mutations in NCC (loss-of-function)
What are human NCC mutations?
Transmembrane spanning domains
Loops in extracellular domain
25th amino acid domain
Red spots (mutations are distributed throughout the protein)
- usually clusters of mutations in most diseases
- no pattern of activity
- slightly different impacts on NCC but basically loos of function
What have Xenopus oocyte studies shown?
e.g. NCC
- functional analysis
- how much radioactive Na is taken up in oocyte
Absorbs less Na across apical membrane
- could impact function of NCC or impact on trafficking of protein
- amount of fluorescence is a lot less
- mutations impact trafficking of channel
- stops NCC getting to membrane
- stops transport
Reduces Na at early distal tubule
How are functional analysis studies done?
Inject RNA
Protein of interest made
What is the typical structure of the xenopus oocyte?
Oocytes 2mm in diameter
Easy to see
Dark side and light side
Oocytes make lots of protein of interest
What do thiazide diuretics do?
Blocks NCC e.g. Chlorothiazide - brings extracellular fluid down - treatment for high blood pressure Side effects like Gitelman's syndrome - K handling and Ca handling may be similar to Gitelman's syndrome
How does carrying one mutation for ROMK, NCC or NKCC 2 protect against hypertension?
Locate impact of being a carrier for Gitelman’s syndrome or Bartter’s syndrome in terms of BP
Blood pressure increases as you grow older
Carrier:
- asymptomatic in terms of kidney function
- but has hypotension in both systolic and diastolic blood pressure than normal population
- at reduced risk of cardiovascular disease
e.g. stroke
- protection against hypertension induced condition at older age
How are the late distal tubule, collecting tubules and cortical collecting duct structurally different but having similar functions?
Concentration of urine
Reabsorption of Na and H2O
Secretion of K and H
What are the late distal tubule and cortical collecting duct composed of?
Two cell types:
Principal and Intercalated
What is the Principal cell involved in?
Na and H2O reabsorption
K and H secretion
What is the Intercalated cell involved in?
alpha-IC and beta-IC
- balance is dynamic
H secretion and reabsorption
HCO3 reabsorption and secretion
What does the apical membrane of the Principal cell contain?
ENaC
ROMK
Aquaporin 2
What does the basolateral membrane of the Principal cell contain?
Na/K ATPase
Kir2.3
Aquaporin 3 and 4
What is the Epithelial Na Channel (ENaC) involved in?
Found in apical membrane and epithelial around the body
Na from tubular fluid to Principal cell
Net reabsorption of Na in kidney
More Na you reabsorb via ENaC, the more K you secrete via ROMK
Bartter’s or Gitelman’s:
- more Na go to late distal tubule
- more Na in tubular fluid
- leads to more reabsorption via ENaC
- leads to hypokalaemia in both patient groups
- still salt wasting but Principal cells are decreasing leve of salt wasting
Aquaporins: Occurs through regulation of number of Aquaporin 2
- driving force for movement is partially through reabsorption of Na bu also high concentration of NaCl is interstitial fluid
What are diseases that can arise from abnormalities in the Principal cell?
Diabetes Insipidus (Aquaporin 2) Liddle's syndrome (ENaC) - hypotension Pseudohypoaldosteronism - Associated with ENaC - Associated with receptor for aldosterone
What is Amiloride?
Diuretics - reabsorb less water - affects ENaC Classified as K sparing molecule Drug of choice for patients of Liddle's syndrome
What is found in the apical membrane of the alpha-IC cell?
active H secretion
What is found in the basolateral membrane of the alpha-IC cell?
AE1
Cl secretion
What does the alpha-IC cell do?
H secretion and HCO3 reabsorption
- Cl recycles in exchange for HCO3 back into plasma
- HCO3 is generated in the cell
- Primary active transport protein ATPase
- Anionic exchangers 1 (AE1)
What mutation causes Distal and Tubular acidosis?
Genetic inheritance )mutations in AE1 of alpha- IC cell
What are the main symptoms of Distal and Tubular acidosis?
Nephrocalcinosis
- stone formation in urinary system (not kidney)
Metabolic acidosis
Nephrolithiasis
What do mutations of AE1 lead to?
Mutations mean mistargeting of protein
- go to basolateral membrane but also to the apical membrane (Not good!)
Some of the new HCO3 lost in tubular fluid
- pH regulation system for extracellular fluid is not as effective - acidosis
What is the main difference between alpha-IC and beta-IC?
AE1 and ATPase swap places
What is the beta-IC cell involved in?
H and Cl reabsorption and HCO3 secretion
- Not many beta-IC cells
- normally has acid load that needs to be secreted
What is the main structure of medullary collecting duct?
Low Na permeability
High H2O and urea permeability in the presence of vasopressin
- not a lot of ENaC
- Many aquaporins: urea is a key component for our ability to concentrate our urine
Where is the medullary collecting duct mostly seen?
In prsence of hormone e.g. vasopressin
What is acute renal failure?
Fall in Glomerular filtration rate over hours/days
- much faster than chronic renal failure
- can die within 3 days without treament
What causes acute renal failure?
three main types:
Pre-renal/renal/post-renal
Impaired fluid and electrolyte homeostasis Accumulation nitrogenous waste - massive in short period of time Lasts ~ i week Treatment ; dialysis (reversible)
What are general symptoms of acute renal failure?
Hypervolaemia
Hyperkalaemia
Acidosis
What is hypervolaemia?
Oliguria due to low GFR
- expansion of extracellular fluid volume
What is hyperkalaemia?
Lack of K secretion
K accumulates
- impact on cardiac excitability
- indication of electrical properties in cell is altered
What is acidosis?
H accumulates
Very severe impact
Depression of central nervous system
Cardiac excitability is the main cause of death
What was found in a case study in which a 32 year old male was in a road traffic accident
Trapped 3 hours with lower limb fractures - compression in muscles in legs Hypervolaemia - hypertension - loss of blood - hypotension is the main failure of acute renal failure Pre-surgery catheter inserted in urethra Urine: Dark-blood then minimal urinary output Plasma K: 7.8 mM - high HCO3: 11mM - low Urea 13mM - high Creatinine 0.19 mM - high - tachycardia
Oliguria is a consequence of hypotension (pre-renal cause) leading to a fall in GFR. What is hypotension a result of?
Poor renal perfusion (pre-renal cause)
What is Rhabdomyolysis?
From compression of muscle
Release myoglobin from damaged muscle
Myoglobin gets into bloodstream
Toxic effect on kidney tubules (renal cause)
What are treatments for acute renal failure?
IV saline - treat hyperkalaemia
- hyperkalaemia is usually dangerous for heart, muscle and nerves
HCO3
- to bring level to normal
Rehydration
- carefully: get BP back up but massive amount of volunme leads to massive expansion of extracellular fluid - hypertension
Dialysis of oliguria persists for more thana few days
