ATP-dependent Pumps and Ion Exchangers Flashcards
What is an Na+ dependent Cl-/HCO3- exchanger (NBC)?
1Na in for 1H+ out, 1HCO3 in for 1Cl- out
Co-transporter, Alkalinises cell = control cell pH/vol
Give an example of an anion exchanger
Cl-/HCO3- exchanger, base extruder = control cell pH/vol
Describe sodium hydrogen exchanger Na+/H+ (NHE)
Acid extruder = control cell pH
Electroneutral 1 Na= in : 1 H+ out exchanger
Regulates cell vol – when proton moves so does water
Inhibited by amiloride
When is a mitochondrial Ca2+ Uniport used?
If Ca gets too high, uses mitochondria uniporter as buffer in attempt to save cell
Describe a sodium calcium exchanger Na+ Ca+ (NCX)
3 Na+ inside for 1 Ca2+ outside
Secondary active transport, exchanger is reversible
Role in expelling Ca2+ in cell recovery, Membrane potential dependent –> polarised = Ca out, depolarised = Ca in
Ischemia = no ATP = Na pump inhibited = high Na = cell depolarises = Ca in = toxic
Which exchanger is not a pump and why?
Sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA)
NOT A PUMP NOT ATTACHED TO PLASMA MEMBRANE
1ATP for 1Ca2+ inside SR/ER, Primary activity transport
What is the Plasma membrane Ca2+ ATPase (PMCA)?
1 ATP for 1 Ca2+ outside the cell, Ca toxic to cells – lots of phosphate from ATP hydrolyses inside cells = crystallise, Primary activity transport
Describe the Sodium-potassium ATPase (Na+-K+-ATPase, ‘The Na pump’)
moves 3 Na out, 2 K in to maintain normal conc gradient, controls pH, cell vol and [Ca2+], provides energy for glucose uptake
high internal K = resting membrane potential (-70mV),
antiport, co-transport
creates Na+ gradient to provide energy for transporters
What happens to the Na Ca2+ exchanger in ischaemia?
The NCX reverses, originally Ca 2+ out and 3Na+ in
No O2 = no ATP = Na K ATPase depleted = high [Na+] = cell depolarisation = now Ca2+ in = high [Ca2+] = toxic
What is the [Ca2+] inside and outside the cell?
Inside = ~0.0001mM Outside = ~1mM
Why is there such a different in [Ca2+] outside to inside the cell?
Ca2+ is toxic = cell death.
Low [Ca2+] allows small conc changes to cause a large response. ~10,000 - 20,000 fold diff
How do you work out folds?
(B-A)/A
(4-2) = 2/2 = 1 –> 1 fold diff between 2 and 4
How would you write 3x10^-6 in full?
0.000003
How is Intracellular [Ca2+] lowered?
PMCA - plasma membrane Ca2+ ATPase
NCX - Na+ Ca2+ exchanger
SERCA - Sarco(endo)plastic reticular Ca2+ ATPase
Mitochondrial Ca2+ uniporter
How is Intracellular [Ca2+] raised?
VOCC - voltage operated calcium channel SOC - store operated channel LGIC - ligand gated ion channel RyR - ryanodine receptor: release Ca2+ from SER GCPR IP3 - release Ca2+ from SER
How does the SERCA - Sarco(endo)plastic reticular Ca2+ ATPase pump work?
uses ATP, 1H+ out for 1Ca2+ in
used when storage is low or residual [Ca2+] high
In general terms how does cell volume regulation occur
cell swelling = extrude ions
cell shrinking = influx ions
every ion moves 6 H2O
Why can Cl-, Na+, K+, Ca2+ be classed as osmolytes?
every ion moves 6 H2O
What are diuretic drugs used for?
block transporters that reabsorb Na+, more lost in urine, more water therefore also lost = helps treat oedema
Why is all the bicarbonate absorbed in the kidneys?
to retain the base when controlling cell pH levels
Why is all the Na reabsorbed in the kidneys?
Na K ATPase creates low intracellular [Na+] = Na+ moves back into cells down conc gradient = all absorbed
