Introduction Flashcards
What % of the membrane is:
Lipids
Proteins
Carbohydrates
Lipids - 42%
Proteins - 55%
Carbohydrates - 3%
Where are Na+ the highest?
In the plasma and interstitial fluid (extracellular)
Where are Na+ the lowest?
Intercellular fluid
Where are K+ the highest?
Intercellular
Where are K+ the lowest?
In the plasma and interstitial fluid (extracellular)
Where are Cl- the highest/lowest?
Highest outside of the cell
Lowest inside
Where are PO4^2- the highest/lowest?
Highest inside of the cell (ATP)
Lowest outside of the cell
Where is HCO3- found?
What is it important for?
In the interstitial fluid, plasma and intracellular fluid
Important pH buffer
Which cells have higher Cl- INSIDE?
Chloride secreting cells in the upper airway epithelial cells
What molecules are transported across the membrane via diffusion?
Lipid soluble molecules
O2, CO2
What molecules are transported across the membrane via transport proteins?
Small molecules and ions
What molecules are transported across the membrane via endocytosis?
Large molecules
What is another name for carrier proteins?
Facilitated transport proteins
What are carriers driven by?
The electrochemical gradient
What are examples of a carrier?
Sodium glucose cotransporter
Ion channels
What are primary active transport proteins?
Pumps
eg. ATPases
ONLY work if ATP is present
What is an important feature about channels?
They are GATED
Which transport proteins facilitate ACTIVE transport?
PUMPS
Which transport proteins facilitate PASSIVE transport?
Carriers and channels
What is active transport?
AGAINST the electrochemical gradient
Channels DIRECTLY hydrolyse ATP to change confirmation of the protein
Requires energy through ATP hydrolysis
Substances bind on one side of the membrane and are released on the other side, as a result of conformational change
What is passive transport?
FOLLOWS the electrochemical gradient
Are INDIRECTLY reliant on the NA/K ATPase to set up the electrochemical gradient
So they are INDIRECTLY reliant on ATP
Secondary active transport proteins
When is ATPase active transport needed?
When there is NO electrochemical driving force or when need to go AGAINST the electrochemical driving force
What is the transport rate of ATPase active transport?
LOW turn-over
What is the structure of Na/K ATPase?
Tetramer:
2 alpha subunits
2 beta subunits
Where is Na/K ATPase found?
Ubiquitous (in nearly EVERY cell in the body)
NOT found in RBC of DOG
What does Na/K ATPase transport?
What does this generate?
3 Na+ OUT
2 K+ IN
Generates a net loss of 1 positive charge from the cell - generating a -ve intracellular charge
What does Na/K ATPase maintain?
What is this important for?
Low Na+ INSIDE the cell
Important to drive carriers and channels, which work with the electrochemical gradient
What is the transport of carriers (facilitated transport proteins) dependant on?
The electrochemical gradient of at least ONE of the substances being transported (usually the Na+ gradient)
What is the turnover of carriers?
High
What can happen to carriers?
Why?
They can become SATURATED
As cannot put any more channels in the membrane
What are the 3 classifications of carriers?
Describe them
1) UNIPORTER
- Transports 1 ion/solute
- DOWN the concentration gradient
2) SYMPORTER (co transporter)
- Transports 2 ions/solutes
- DOWN the concentration gradient
3) ANTIPORTER (exchanger)
- Transport one ion IN
- Transport on ion OUT
What is an example of a uniporter?
Glucose transport protein
What is an example of a cotransporter?
Sodium/glucose cotransporter
What is an example of an exchanger?
Na/H exchanger
What is the turn over of ion channels?
VERY high
Why can the patch clamp technique be used?
When ions travel through an ion channel they generate a CURRENT as the ions are CHARGED
This current can be measured
Are ion channels selective or non-selective?
BOTH
- Can be selective for a certain ion (eg. Na+, Cl- etc.)
- Can be non-selective for a certain group of ions (cation selective, anion selective)
Who derived the patch clamp technique?
When?
Nehr and Sakmann
In 1993
What can be identified using the patch clamp technique? (6)
- What ion channels are present
- What regulates these ion channels
- Can identify SINGLE channels
- Can identify the physiological function of the channels
- Can identify pathophysioloigical CHANGES to a channel which cause disease
- Can look at the impact on the cell when overexpress mutated channels
Describe the process of the patch clamp technique
- Glass electrode
- Chloride metal wire attached to equipment
- REFERENCE electrode sat in bath but also attached to equipment
- Electrode looks at the DIFFERENCE between the 2 electrodes
1) Bring glass electrode to touch cell membrane
2) Seal cell membrane around the glass electrode
3) Look at current flow
As well as single ion channels, what can the patch clamp technique look at?
What is the method for this?
ALL the channels in the cell membrane
1) Pulses of suction to rupture the cell membrane
2) Solution in patch pipette - now intracellular solution
3) Can measure TOTAL current flow across the whole membrane
4) Clamp the potential and measure the current
What equation which describes the total current?
I = N.Po.g. (Vm-Ei)
I = total current N = number of channels in the membrane Po = open probability of the channels g = single channel conductance (a constant) Vm = membrane potential Ei = Equilibrium potential
What is the ‘open probability’ of a channel?
What scale is it measured on?
How often the channel is open
Measured on a scale 0-1:
0 = never open
1 = always open
What 3 things can change the open probability of the channel?
1) Adding a phosphate
2) pH
3) G protein
What is the equilibrium potential of an ion AKA?
Nerst potential
What is Vm-Ei?
The POTENTIAL of the membrane (DRIVING FORCE of the ions)
What is the relationship between driving force/potential and current?
The bigger the driving force, the bigger the potential
What things can increase I (the total current)?
1) Increase no. of channels
2) Increase open probability (Gprotein, pH, phosphorylation)
3) Vm-Ei (driving force)
- Can increase membrane potential by opening/closing other channels which are electrogenic
What is the structure of a Kv channel (voltage gated potassium channel)?
6 TM domains in each subunit
4 subunits together to make a functional channel
N and C are INTRACELLULAR
What is the structure of a Kir channel (inwardly rectifying potassium channel)?
2 TM domains in each subunit
4 subunits to make functional channel
N and C are INTRACELLULAR
What is the structure of a Nav channel?
24 TM in blocks of 6
N and C are INTRACELLULAR
What is the structure of a Cav channel?
Same as Nav:
24 TM in blocks of 6
N and C are INTRACELLULAR
What is the structure of a Ach channel?
4 TM
N and C are EXTRACELLULAR
What is the structure of a CFTR Cl- channel?
12 TM
N and C are INTRACELLULAR
What is the structure of a bacterial K+ channel?
Crystallised
Homologous to human Kir channel:
- 2 Tm domains
- 4 subunits to make functional channel
- Pore in the middle where a TRAIN of K+ ions travel through
Who discovered the structure of the bacterial K channel?
Rod MacKinnon in 1998
What is the intracellular concentration of Cl-?
6 mM
What is the extracellular concentration of Cl-?
100 mM
