Flashcards in Cell homeostasis Deck (58)
What gradient is important to drive secondary active processes in the cell?
The Na+ gradient (low intracellular and high extracellular
What is the concentration of Na+ INSIDE the cell?
What is the concentration of Na+ OUTSIDE the cell?
Which transport protein keeps intracellular Na+ low?
Na/K ATPase (pump)
Describe the apical and basolateral membranes of the epithelial cell in the thick ascending limb
1) Na/K ATPase keeps intracellular Na low
2) K+ channel
3) CLCK (Cl- out)
1) NKCC (Na, K, Clx2 in)
2) ROMK (K out)
In the thick ascending limb, what produces the driving force for NKCC?
Na/K ATPase - keeping intracellular Na+ low
ROMK - recycles out K+
In the thick ascending limb, what happens if [Na+] is increased inside the cell?
1) NaCl reabsorption inhibited as NCKK can't work
2) Osmotic gradient across the thick ascending limb decreases
3) Less water absorbed (follows Na)
4) Increased salt wasting and diuresis
What is Ena?
What happens, with regards to the action potential, if [Na+] is increased INTRACELLULARILY?
1) Ena becomes ~30mV
2) Reduced electrochemical gradient and driving force for Na+ into the cell
3) Take LONGER for the action potential to develop and the PEAK will not be as high
4) Slower conduction of the action potential and problems with propagation
What is the extrusion of 3Na and uptake of 2K by Na/K ATPase coupled to?
The hydrolysis of ONE ATP
What is the model of Na/K pump action?
1) Na+ binds to cleft on the INTERNAL side of the pump
2) Hydrolysis ATP --> ADP
3) Phosphorylation of the pump - causing a conformational change
4) Binding cleft exposed to the OUTSIDE of the cell
5) Na+ leaves and K+ binds
6) Pump loses phosphate group - returns to its original confirmation
7) Cleft exposed to INTERNAL environment
8) K+ leaves cleft and Na+ bind
What does the rate of transport of the Na/K ATPase pump depend upon?
1) SATURATION - rate is saturable by [Na]i and [K]o
2) Metabolic rate of the cell - rate is saturable by [ATP]
What inhibits the Na/K pump?
How does Na/K maintain a the inside of the cell to be NEGATIVE?
Which factor plays more of an importance?
1) Electrogenic transport: 3+ out, 2+ in
- Makes inside more negative
2) Accumulation of K+ inside the cell (by Na/K ATPase transporting them in)
- Driving force for K+ to leave through OTHER channels
- Make intercellular more negative
- MAJOR FACTOR
What allows directional transport in the collecting duct?
Amiloride sensitive channels (NHE1) are on the APICAL membrane
Na/K ATPase is on the basolateral membrane
What produces depolarisation in excitable cells?
What is this recycled by?
Recycled by the Na/K ATPase
What does Na+ drive in the kidney?
The REABSORPTION of many OTHER ions
What is the concentration of INTRACELLULAR Ca2+?
What is the concentration of EXTRACELLULAR Ca2+
What is the difference between intracellular and extracellular concentration of Ca2+?
10,000 fold difference
(Extracellular concentration in 10,000 more than intracellular concentration)
What is Eca?
(Double that of Na and +61mV)
Why is Ca2+ important?
SECONDARY messenger in many signalling pathways
What does Ca2+ release from stores cause in the pancreatic acinar cell?
Fusion of vesicles to the membrane and release of enzymes
What 2 mechanisms help to keep Ca2+ concentration low?
1) Na/Ca Exchanger
2) Ca2+ ATPase
What does the Na/Ca exchanger do normally?
How can this differ?
Exchange 3 extracellular Na for 1 intracellular C (Na in, Ca out)
Differs depending on the gradients set up - eg. this is reversed in the heart (Na out Ca in)
How can a 10 fold Na+ gradient keep Ca2+ in the cell so low when the Ca2+ gradient it 10,000 fold?
- 3 Na+ for every 1 Ca+
- Means the effect of the Na+ gradient is CUBED - giving a 1,000 fold Na+ gradient
- Membrane potential gives another 10-fold Na+ gradient
- 1,000 x 10 = 10,000
- Matches the 10,000 fold Ca+ gradient
What family is the Na/Ca exchanger part of?
How many forms of the Na/Ca exchanger exist in mammals and what are they called?
What family is the Ca pump a family of?
What transport protein is also in this pump?
Na/K pump is also in this family