Lecture 5 - Intracellular PH And Cellular Volume Flashcards
What is normal plasma/serum pH?
7.35 - 7.45
What are the 2 major organs responsible for maintain acid base balance?
Lungs-Respiratory balance
Kidneys-Metabolic balance
What is the pH limits of human tissue survival?
6.8 - 7.8
If the concentration of H+ doubles how much does the pH change?
Decreases by 0.3
Why is it so important for pH to be regulated tightly?
Can change electrical charge on proteins
Disrupt electrostatic interactions, hydrogen bonds
Altering protein structure and function
May change structure of binding sites for substrates
What is normal cytoplasmic pH?
7.2
Why do lysosomes and endosomes have an acidic pH?
Important in degradation of proteins and recycling of receptors
What is the significance of cytoplasmic pH being lower than plasma pH?
There’s a concentration gradient between the cell and the plasma giving H+ the drive to move out of the cell
How does tissue ischaemia lead to cytoplasmic pH dysregulation?
Reduced blood flow = reduced O2 to cells
Reduced O2 = increased anaerobic glycolysis = more lactic acid = higher [H+] in the cell
How does the cell becoming more acidic in tissue ischaemia lead to altered cell function or apoptosis?
Increased [H+] = over activation of Na+/H+ exchanger (NHE)
Leads to Na+ overload/influx
Na+/Ca2+ exchanger activated
Overload of Ca2+
Ca2+ activates unwanted enzymes
Caspases activated = apoptosis
What is Dents disease?
Proximal tubule dysfunction and progressive renal failure
What causes Dents disease?
Mutated Chloride proton exchanger + defective endocytosis due to impaired acidification
Normally, which way is the electrochemical gradient across the membrane of a (polarised) cell compared to the blood?
Cells usually more negative inside
Extracellular usually more positive
What is the main cause of intracellular pH decreasing (acidification)?
Electrochemical gradient
(H+ favoured to move into more negative cell and HCO3- more likely to move out)
During metabolism which molecule usually lead to production of protons and what is this equilibrium reaction?
CO2
CO2 + H2O ——- H2CO3
H2CO3 ——- H+ + HCO3-
What are the 3 buffer systems regulating intracellular pH?
Bicarbonate buffer system (Most important)
Phosphate buffer system
Proteins
What needs to accompany buffer systems to regualte intracellular pH?
Dynamically regulated transport processes
What are some important acid extrudes essential in regulating intracellular pH?
NHE (Na+/H+ exchanger)
Na+ dependant Cl-/HCO3- exchanger
How does NHE affect cell pH?
Secondary active transporter
Na+ moves into cell H+ moves out of cell
Alkalinises the cell
How does a Na+ dependant Cl-/HCO3- exchanger affect cellular pH?
Na+ transports HCO3- into cell
Cl- with some H+ removed from cell
Removal of HCO3- reduces [H+] in cell as well as removing H+
What is an example of a base extruder?
Cl-/HCO3- exchanger (an AE anion exchanger)
How does an AE act as a base extruder regulating cellular pH?
HCO3- released from cell, Cl- brought into cell
Decreasing Intracellular [HCO3-] shifts equilibrium increasing [H+]
Acidification of cell
Which 3 exchangers/cotransporters are important in regulating cell volume?
NHE (Na+/H+ exchanger)
NBC (Na+ bicarbonate chloride cotransporter
AE (HCO3- / Cl- exchanger)
Which transporter is important in ensuring extracellular [Na+] is greater than intracellular?
Na+/K+ ATPase (Sodium pump)
Maintains Na+ gradient to provide energy for secondary/tertiary active transporters
Why is an AE not a secondary transporter?
Not determined by the concentration of Na+
In terms of activity how does the activity of NHE and NBC change as Intracellular pH becomes more acidic?
NHE activity increases
NBC activity increases (sodium bicarbonate transporter) (moves Na+ and HCO3- into the cell)
What is the function of NHE?
Brings Na+ into cell
Pumps H+ out of cell
What is the role of NBC?
Brings Na+ and HCO3- into cell
Pumps H+ and Cl- out of cell
What is the role of AE?
Brings Cl- into cell
Pumps HCO3- out of cell
Why are NHE and AE very sensitive to pH changes?
PH must be maintained tightly
How does the activity of NHE, NBC and AE change as pH gets more alkaline?
NHE decreases
NBC decreases
AE increases
Why does a cell need to be able to regulate its volume?
Excess swelling = jeopardises membrane integrity
Shrinking and swelling = cytoskeleton interfered with
Proteins need correct hydration
What is meant by a cell being in a hypertonic solution?
Solution osmolarity high
More water in cell moves out, cell shrinks
What is cell shrinkage called?
Plasmolysis
What is a hypotonic solution?
Solution osmolarity lower than cell
Water moves into cell, cell swells
Why is hypernatremia and hyponatremia dangerous?
Changes in plasma osmolarity lead to cell shrinkage or swelling
What happens to water when solutes leave a cell?
Water follows and moves out
What are the cells mechanisms for a cell to resist swelling (carrying out Regulatory Volume Decrease? (acute response)
Osmotically active ions effluxed (water follows)
K+ stretch activated channels
Cl- Stretch activated channels
K+/Cl- Co-transporter
What are the cells mechanisms for a cell to resist shrinking (carrying out Regulatory Volume Increase? (acute respone)
Osmotically active particles influxed
Na+/Cl- cotransporter
Na+/K+ 2Cl- cotransporter
NHE may be activated removing H+ bringing Na+ in
How does synthesis of organic solutes help prevent cell shrinkage? (Chronic response)
Increases solute concentration in the cell
Water moves into cell
What is the chronic response to resistaning swelling (regulatory volume decrease)?
Efflux and reduced synthesis of organic osmolytes (glucose)
