MR 2 Membrane Permeability Flashcards
What kinds of molecules can pass through membranes?
hydrophobic and small, uncharged, polar molecules
What kinds of molecules cannot pass through membranes?
Large, uncharged, polar molecules and ions
What is passive diffusion?
Dependent on permeability and concentration, rate of passive transport increasing linearly with increasing concentration gradient
What is faciliatated diffusion?
Where permeability of membrane for a substance increased by incorporation of a specific protein in the bilayer. Models include carrier molecules(ping-pong) and protein channels.
What is active transport?
Transport of ions or molecules against concentration and or electrical gradient, requiring energy from the hydrolysis of ATP
What type of free energy change do active processes have?
positive
What are co-transporters?
Transporters that transport more than one molecule?
What is a uniport?
transports 1 molecule in 1 direction
What is a symport?
Transports more than one molecule in the same direction
What is an antiport?
Transports more than one molecule in opposite directions
What are the extra and intracellular Na+ concentrations?
outside- 145mM inside- 12mM
What are the extra and intracellular K+ concentrations?
outside- 4mM inside- 155mM
What are the extra and intracellular Ca2+ concentrations?
outside-1.5mM inside 10-7M= 0.1um
What are the extra and intracellular Cl- concentrations?
outside- 123mM inside- 4.2mM
What does Na+/K+ ATPase do?
antiport using energy from ATP to move 2K+ into the cell and 3Na+ out of the cell to form Na+ and K+ gradients necessary for electrical excitability and to drive secondary active transport
For what processes does the sodium potassium pump drive secondary active transport?
pH control regulation of cell volume Na+ absorption in epithelia Nutrient uptake e.g glucose from small intestine
What are K+ channels mainly responsible for?
Diffusion down conc grad set up by the sodium potassium pump, K+ moving out of cell, is mainly responsible for the resting membrane potential of -70mv
What does Plasma Membrane Ca2+-ATPase(PMCA) do?
Uses ATP to expel residual Ca2+ from the cell in exchange for H+ (antiport). high affinity, low capacity
What does Sarco(endo)plasmic Reticulum Ca2+-ATPase(SERCA) do?
Accumulates Ca2+ into SR/ER in exchange for H+ using ATP (antiport) High affinity, low capacity
What is secondary active transport?
Facilitated diffusion using a concentration gradient set up by an active transport process
What does the sodium calcium exchanger (NCX) do?
Expels 1 Ca2+ in exchange for 3Na+(antiport) via secondary active transport using the Na+ gradient set up by the sodium potassium pump. Responsible for removing most Ca2+. Activity is membrane potential dependent
Is NCX electrogenic?
Yes, current flows in direction of Na+ gradient
What happens in ischaemia relating to NCX?
ATP depleted Sodium potassium pump therefore inhibited Na+ accumulates in cell leading to depolarisation NCX reverses Na+ moves out and Ca2+ moves in High Ca2+ is toxic
What happens to CFTR in diarrhoea?
In gut epithelial cells its activated by protein kinase A, it pumps out more Cl- into the lumen causing water to follow causing diarrhoea
What are the acid extruders in cell pH control?
Na+/H+ exchanger (NHE) Na+ dependent Cl-/HCO3- exchanger (NBC- sodium bicarbonate cotransporter) note: uses Na+ grad
What is the alkali extruder?
Cl-/HCO3- exchanger (AE-anion exchanger) (Band 3)
What transporters cause alkali influx?
NBC Na+/HCO3- co transporter (symport)
How is cell volume regulated?
Transport of osmotically active ions e.g Na+, K+, Cl- or organic osmolytes (amino acids) in and out of cell causing water to follow
What are the mechanisms to resist cell swelling?
What are the mechanisms to resist cell shrinking?
Outline bicarbonate resorption by the proximal tubule
What transporter do loop diuretics block and where is this in the kidney?
NKCC2
thick ascending limb
What transporter to thiazides block and where in the kidney does this occur?
NCCT Na+/Cl- co-transporter
distal convoluted tubule
What protein does amiloride block and where in the kidney does this occur?
Epithelial sodium channel
distal convoluted tubule
Why do you get hypertension in hyperaldosteronism?
aldosterone stimulates the reuptake of ions in the cortical collecting duct by binding with glucocorticoid receptors so too many ions are taken back
How does spironolactone act?
glucocorticoid receptor antagonist blocking aldosterone from activating receptors in the cortical collecting duct and so reducing ion reuptake and hypertension.
What transporters raise intracellular Ca2+
Facilitated diffusion:
Receptor operated Ca2+ channels (ROC)
Voltage operated/gated Ca2+ channels (VOCC/VGCC)
IP3 gated Ca2+ channels
Ca2+ induced Ca2+ release (CICR)
Store operated Ca2+ channels (SOC)
Mitochondrial Ca2+ uniporters
Secondary active transport: NCX in reverse in depolarised cells
