ICPP 4

Question 1

What is the effect of caffeine on drugs?

Answer 1

It increases blood flow and heart rate which increases efficacy of drugs

Question 2

Define membrane potential.

Answer 2

The magnitude of electrical charge that exists across a plasma membrane, expressed as the potential inside the cell relative to the EC solution.

Question 3

All cells have a ______ resting membrane potential.

Answer 3

negative

Question 4

There are 2 important factors essential for membrane potential to be established, what are they?

Answer 4

1. Asymmetric distribution of ions across membrane

2. Selective ion channels in the plasma membrane

Question 5

What are the 3 ions which are most important in membrane potential?

Answer 5

K+, Na+ and Cl-.

Question 6

K+ moves in which direction, what does this lead to?

Answer 6

K+ moves out of cells which leads to the generation of an electrical gradient and charge separation, which is the basis of resting membrane potential.

Question 7

Why will K+ want to move back into the cell,against its chemical gradient?

Answer 7

The inside of the cell is more negative, so it will want to move down the electrochemical gradient to the negative side. But it cannot.

Question 8

Which channels dominate the membrane at rest?

Answer 8

Open K+ channels

Question 9

What is the nernst equation used to calculate?

Answer 9

The membrane potential of an ion, given the intracellular and extracellular concentrations.

Question 10

Which ions contribute to the membrane potential of around -70mV?

Answer 10

Na+,K+ and Ca2+

Question 11

Na+ and Ca2+ both have a ________ equilibrium potential.

Answer 11

Positive.

Question 12

K+ has a negative equilibrium potential. If the membrane was permeable this ion alone, membrane potential would be….

Answer 12

-95mV

Question 13

Not all cells have a rmp of -70mV, why is this?

Answer 13

Increased contribution from other ions, less K+ selective.

Question 14

Cardiac muscle and nerve cells are more selective to K+, how is this reflected in their membrane potential?

Answer 14

Their mp is closer to the K+ equilibrium potential

Question 15

What is depolarisation?

Answer 15

A decrease in the size of the membrane potential from its normal value.
Interior becomes less negative.

Question 16

What is hyperpolarisation?

Answer 16

An increase in the size of the membrane potential, cell interior becomes more negative.

Question 17

Increasing the membrane permeability to a particular ion will move the membrane potential towards what? Give an example.

Answer 17

Towards the equilibrium potential for that ion.

E.g in depolarisation when membrane becomes more permeable to Na+, the membrane potential rises towards ENa+.

Question 18

The opening of which channels will cause hyperpolarisation?

Answer 18

K+ and Cl-, as these both have negative eq. Potentials.

Question 19

The opening of which channels will cause depolarisation?

Answer 19

Na+ and Ca2+ as they both have positive equilibrium potentials.

Question 20

Which equation takes into account the contribution of more than one ion?

Answer 20

GHK

Question 21

Define conductance.

Answer 21

How permeable a membrane is to an ion

Question 22

Give an example of a less selective channel.

Answer 22

nACh receptor is a cation channel, lets both Na+ and K+ through.

Question 23

Where is an example of mechanical gating?

Answer 23

Hair cells in the inner ear

Question 24

What types of receptors are involved in fast transmission?

Answer 24

Receptor protein is also an ion channel, transmitter binding causes immediate opening.

Question 25

What do inhibitory transmitters cause?

Answer 25

Hyperpolarisation .. prevent action potential from firing.

Question 26

What are the 2 patterns associated with slow synaptic transmission?

Answer 26

G-protein coupling - g-protein opens channel
Gating via an intracellular messenger - g-protein activated enzyme and signal cascade which then leads to channel opening

Question 27

Give an example of an electrogenic pump.

Answer 27

Na+/K+ ATPase. Net loss of one positive charge each time.

Question 28

How does a beta-cell secrete insulin?

Answer 28

Glucose enters via GLUT2 transporter and is metabolised to produce ATP.
ATP binds to the ATP-sensitive K+ channel, causing it to close.
Membrane depolarises
VOCC Ca+ channels open, calcium influx causes insulin vesicles to fuse with membrane.

Question 29

How do sulphonylurea’s act to treat type 2 diabetes?

Answer 29

Sulphonylurea receptor is physically bound to the ATP-sensitive K+ channel. When the drug binds to the receptor, it causes the K+ channel to close regardless of glucose concentration.

Question 30

Outline the 4 stages of the cardiac action potential.

Answer 30

Stage 4. K+ efflux through open rectifier channels. RMP = -90mV
Stage 0. Na+ influx through open fast Na channels
Stage 1. Transient K+ channels open and K+ efflux returns TMP to 0
Stage 2. L-type calcium channels open, balanced by delayed rectifier K+ channels, plateau.
Stage 3. Calcium channels close and delayed K+ rectifier channels retiring to RMP.

Question 31

What are the properties of cardiac ion channels?

Answer 31

1. Only permeable to ONE type of ion
2. Time -dependence - some ion channels close a fraction of a section after opening (fast Na+ channels)
3. Voltage-sensitive gating - specific channels open and close in a small MP range.

Question 32

Define equilibrium potential.

Answer 32

For each ion, the equilibrium potential is the membrane potential where the net flow through any open channel is 0.

Question 33

How would you measure the membrane potential?

Answer 33

using a microelectrode