M&R 2.2 - ATP Dependent Pumps And Ion Exchangers Flashcards
What are the functions of the sodium ion pump?
- Form Na+K+ gradient (used in membrane potentials)
- Promotes secondary active transport (pH control, cell volume and Ca2+ regulation, Na+ absorption and nutrient uptake)
What is the Na+Ca2+ exchanger otherwise known as?
NCX
What is the ratio of ion transport of NCX? What happens as a result of this?
- 3 Na+ into cell : 1 Ca2+ out of cell
- Membrane becomes electrogenic so the current runs in the direction of the Na+ gradient
What is the function of NCX?
Expels intracellular Ca2+ during cell recovery from signalling
What happens when NCX becomes depolarised?
- Works in reverse (3Na+ out, 1Ca2+ in)
- Lead to a high concentration of extracellular Na+ and high concentration of intracellular Ca2+
What happens to NCX during ischaemia/ after reperfusion?
The depletion of ATP causes it to become partially depolarised which can produce toxicity
What is the Na+H+Exchanger otherwise known as?
NHE
What is the ratio of ion exchange of NHE?
- 1 Na+ in: 1 H+ out so is electroneutral
What are the functions of NHE? What is it activated by?
- pH regulation (is an acid extruder)
- Cell volume regulation
- Drug target for Amiloride
- Activated by growth factors
Name the two bicarbonate transporters and give their shorthand terms
- Na+bicarbonate-chloride cotransporter (NBC)
- Anion exchanger (AE)
What is the function of NBC and how is this achieved?
- Alkalinises cell
- 1 Na+ and 1 HCO3- in : 1 H+ and 1 Cl- out
What is the function of AE and how is this achieved?
- Acidifies cell
- 1 HCO3- out : 1 Cl- in
What the full name of PMCA?
Plasma membrane Ca2+ ATPase
What are the functions of PMCA?
- Removes 1 Ca2+ from cell and brings 1 H+ in
- Removes residual Ca2+ by having a high affinity but a low capacity
What is the full name of SERCA?
Sarco(endo)plasmic reticulum Ca2+ ATPase
What are the functions of SERCA?
- Removes 1 H+ and brings 1 Ca2+ in
- Accumulates Ca2+ in sarcoplasmic/endoplasmic reticulum by having a high affinity but a low capacity
What kind of active transporter are SERCA and PMCA?
- Primary active transporter
- Use ATP
What are the intracellular and extracellular concentrations of Ca2+?
- Intracellular = 50-100nM
- Extracellular = 2mM
Which three transport methods contribute to the transport of calcium ions? Why does there need to be so many?
- Primary active transport e.g. SERCA
- Secondary active transport e.g. NCX
- Facilitated transport e.g. VOCC
- If only one was used, the appropriate concentrations wouldn’t be able to be reached
Which transporters contribute to the control of cellular calcium levels?
- PMCA
- SERCA
- NCX
- Mitochondria Ca2+ uniports
What is the function of the mitochondrial Ca2+ uniports?
- Buffer away from cytoplasm when concentrations of Ca2+ are high
- Move H+ into inter membrane space which causes an electrical gradient
Which transporters are acid extruders?
- NHE - removes H+ so is protective in highly metabolising tissues
- NBC
Which transporters are base extruders?
AE - chloride is also brought in therefore acidifying
How is cell volume regulated? In what environment can this be achieved?
- Transport of osmotically active ions e.g. Na+ to which water follows
- Has to be done in an ELECTRONEUTRAL environment
What causes swelling and shrinkage of the cell?
- Swelling = INFLUX of ions therefore more water inside
- Shrinkage = EXTRUSION of ions therefore more water outside
Where does renal bicarbonate absorption happen? What is the aim of this?
- Proximal tubule of the kidney
Goals are:
- H2CO3 retention for pH buffers
- pH and cell volume regulation
How is Na+ retained in the proximal tubule?
- NHE transports Na+ into cell from lumen of proximal tubule
- Na+ pump transfers Na+ into the capillary from the cell
How is H2CO3 retained in the proximal tubule?
- NHE exchanges H+ for Na+
- H+ combines with HCO3- to make H2CO3
- H2CO3 is broken down by carbonic anhydrase to form H2O and CO2
- Diffuse readily across membrane and recombine in cell
- H2CO3 transported into capillary by AE
Which transporter is targeted in the thick ascending limb of the kidney during diuretic treatment? What is the effect of this?
- NKCC2 (Na+K+Cl- move in)
- Is inhibited when loop diuretics bind
- Limits reuptake of Na+ therefore less water reabsorbed
- Blood volume is decreased
- Decreases blood pressure
Which transporters are targeted in the distal convoluted tubule of the kidney during diuretic treatment? What is the effect of this?
- Thiazide inhibits Na+Cl- cotransporter and does the same as loop diuretics
- Amiloride inhibits Epithelial Na+ Channel and does the same as loop diuretics
Which transporters are targeted in the cortical collecting duct of the kidney during diuretic treatment? What is the effect of this?
- ENaC
- Na Pump
- ROMK
- Spironolactone inhibits therefore inhibiting aldosterone
What is the function of aquaporin? What stimulates this?
- A water channel, ensures efficient water uptake along with Na+
- Stimulated by ADH
What is Na+K+ATPase otherwise known as?
Sodium pump
