Sesh 3: Membrane Permeability

Question 1

What kind of scale are permeability co-efficients on?

Answer 1

A log scale

Question 2

Passive transport depends on what 2 factors?

Answer 2

Permeability and conc gradient

Question 3

What type of channel is the nAChR?

Answer 3

Ligand-gated ion channel

Question 4

What charge is delta G for active transport?

Answer 4

+ve

Question 5

What charge is delta G for passive transport?

Answer 5

-ve

Question 6

How does delta G increase with increasing concentration ratio/ membrane potential?

Answer 6

Linearly

Question 7

Is active or passive transport more efficient?

Answer 7

Active

Question 8

What is the concentration of Ca2+ inside and outside of the cell?

Answer 8

Inside=100nm

Outside=1mM….10,000 X conc difference

Question 9

What is the conc of Na inside and outside of the cell?

Answer 9

Inside=12mM

Outside=145mM

Question 10

What is the concentration of K+ inside and outside of the cell?

Answer 10

Inside=155mM

Outside=5mM

Question 11

What is F1F0-ATPase?

Answer 11

An ATP synthase in mitochondria, that generates ATP (active transport in reverse) to move H+ into the intermembrane space.

Question 12

Define co-transport.

Answer 12

> 1 molecule or ion transported per reaction cycle. Can be symport (in same direction) or antiport.

Question 13

How many ions of Na+ and K+ does the Na/K ATP-ase move in what direction?

Answer 13

• 3Na+ out of cell

- 2K+ in

Question 14

What is the effect of ouabain on Na+ and K+ transport?

Answer 14

Blocks the Na/K ATP-ase

Question 15

PMCA has a high ______ but low _______.

Answer 15

1. Affinity

2. Capacity

Question 16

SERCA has a high ______ but low _______.

Answer 16

1. Affinity

2. Capacity

Question 17

What type of transport occurs via the Na/Ca exchanger (NCX)?

Answer 17

Secondary active transport (uses Na gradient set up by Na/K pump). Antiport.

Question 18

What transport occurs via SGLT in the gut?

Answer 18

Secondary active transport. Symport- 2 Na+ and 1 glucose moved into the cell.

Question 19

What type of drug is fluoxetine?

Answer 19

SSRI- inhibits pre-synaptic serotonin re-uptake to act as an anti-depressant.

Question 20

Why does electrical imbalance occur in CF patient cells?

Answer 20

Mutation in CFTR gene means the channel misfolds and doesn’t insert into the membrane….less Cl- efflux, but Cl- still entering the cell.

Question 21

Where are ATP-dependent pumps found?

Answer 21

Have to be on the plasma membrane to be called pumps.

Question 22

Why can cells signal using small changes in intracellular calcium?

Answer 22

There is a 10,000X concentration difference in Ca2+ across the membrane, therefore even small changes in intracellular Ca2+ can cause a response.

Question 23

The NCX has a high _______ but low ________.

Answer 23

1. Capacity

2. Affinity

Question 24

Is NCX electrogenic?

Answer 24

Yes. 3 Na+ moved in, and 1 Ca2+ moved out, so cell gains 1 +ve charge per transport cycle.

Question 25

What happens to the NCX when the membrane depolarises?

Answer 25

Reverses....3Na+ transported out for 1 Ca2+ transported into the cell. Helps return intracellular [Na+] to resting levels.

Question 26

What can happen to the NCX in ischaemia/reperfusion?

Answer 26

ATP is depleted, so the Na/K pump is inhibited...Na accumulates intracellularly, causing the membrane to depolarise and NCX to reverse. Ca2+ is then transported into the cell, which can be toxic.

Question 27

Ion transporters also regulate cell _________.

Answer 27

Volume...water follows osmolyte movement.

Question 28

What are 2 examples of acid extruder transporters?

Answer 28

1. Na/H exchanger (antiport) | 2. Na-bicarbonate-chloride co-transporter (Na/HCO3 in; HCl out)

Question 29

What transporter does cell alkalinisation activate?

Answer 29

Anion exchanger (HCO3 out, Cl in)

Question 30

When osmotically-active ions move, how many molecules of water are taken with them?

Answer 30

6 H2O

Question 31

Why does reabsorption need to happen in the nephron?

Answer 31

To prevent excess ion and water loss. Prevents dehydration.

Question 32

Which ion circles in and out of the proximal tubule cells to drive bicarbonate reabsorption?

Answer 32

H+ -In via free diffusion of H2O, out via Na/H exchanger

Question 33

What transporter is responsible for Na+ uptake in the thick ascending limb of the loop of Henle?

Answer 33

NKCC2

Question 34

What transporter do loop diuretics block? Give an example of this type of diuretic.

Answer 34

NKCC2 in thick ascending limb of loop of Henle...block Na+ reabsorption and therefore cause diuresis. For mild hypertension. E.g. Furosemide

Question 35

How is glucose transported into the blood from the gut?

Answer 35

- Apical SGLT1 transporter= symporter, uses secondary active transport to bring 1 glucose in with 2 Na+ - Basolateral- GLUT2 channel- glucose passes into blood via facilitated diffusion

Question 36

How is glucose transported into skeletal muscle, brain and adipose tissue, and how does insulin affect this transport?

Answer 36

- Facilitated diffusion via apical GLUT 1, as glucose concentration gradient favours uptake - Insulin binds insulin receptors which cause GLUT4 to translocate apically from intracellular sites, to increase glucose uptake.

Question 37

Why doesn't glucose efflux from cells when circulating glucose levels decrease?

Answer 37

Glucose is rapidly used up/converted to other molecules e.g. Glycogen within the cell, so that the concentration gradient is not reversed.