Channel Structure and Modulation

Question 1

What is the role of the cell plasma membrane?

Answer 1

Acts as a barrier separating the contents of the cell from the outside

Question 2

How are the distribution of ions maintained between the outside and the inside?

Answer 2

by ionic pumps and exchangers and so consumes energy.

Question 3

What is the result of the ionic imbalance?

Answer 3

An electrical potential difference between the cytoplasm and the external medium.

Question 4

How do the cells use the electrochemical gradients?

Answer 4

By allowing ion flow across the cell membrane under well-controlled conditions.

Question 5

What do the ion channels mediate?

Answer 5

The ion transfer in the cell

Question 6

Describe the process of diffusion?

Answer 6

Dissolved ions distribute evenly. Ions flow down the conc. gradient when the channels are permeable to this ion and there is a conc. gradient across the membrane.

Question 7

Describe the process of the electrical movement of ions?

Answer 7

Electrical current influences the ion movement. Resistance=1/electrical conductance.

Question 8

What is the distribution of the potassium ions across the membrane?

Answer 8

Potassium are more conc. inside. 5mM (outside):100mM (inside) Negative Eion

Question 9

What is the distribution of the sodium ions across the membrane?

Answer 9

Sodium more conc. outside. 150: 15 (mM) Positive Eion

Question 10

What is the distribution of calcium ions across the membrane?

Answer 10

Calcium is more conc. outside. 2: 0.0000002 (mM) Positive Eion

Question 11

What is the distribution of the chloride ions across the membrane?

Answer 11

More conc. outside. 150: 13 (mM) Negative Eion

Question 12

Name the two ways in which the electrochemical gradient is created?

Answer 12

1. Active transport (sodium pump) 2. Selective membrane permeability to certain ions and molecules.

Question 13

What ions are movement during rest membrane potential?

Answer 13

Sodium will tend to leak in and potassium to leak out.

Question 14

What ion is said to be permeable to the cell?

Answer 14

Potassium only.

Question 15

How is the resting membrane potential -65mV?

Answer 15

Due to the potassium being pumped out at rest

Question 16

When is the potassium ions at equilibrium?

Answer 16

When the concentration and electrical gradients balance.

Question 17

When is equilibrium achieved?

Answer 17

When the movement down conc. gradient equals movement down electrical gradient.

Question 18

What is the importance of the nernst equation?

Answer 18

Gives the value of the membrane potential at equilibrium.

Question 19

What is the Nernst equation?

Answer 19

Ek = -RT/zF . ln [K]i/ln[K]o

Question 20

What receptor is used to distribute the potassium and sodium ions?

Answer 20

Sodium-potassium ATPase

Question 21

Why isn’t the resting membrane potential equal to the resting potassium equilibrium (-80mV)?

Answer 21

As there is always some leakage of sodium at rest

Question 22

How can some ions have a large conc. gradient but little influence in the overall potential?

Answer 22

As the membrane is less permeable to that ion.

Question 23

What does the nernst equation display?

Answer 23

The theoretical balance between electrical and conc. gradients.

Question 24

What does the goldman equation display?

Answer 24

The real world situation of finite and variable ionic permeabilities.

Question 25

What is the goldman equation?

Answer 25

Vm= -60 log (Pk [K]i+Pna[Na]i + Pcl [Cl]o / Pk[K]o + Pna [Na]o+Pcl [Cl]i)

Question 26

Why is the chlorine outside on the top line of the goldman equation instead on the bottom like the potassium and sodium?

Answer 26

Due to its ionic charge being negative.

Question 27

Describe the characteristics of an action potential?

Answer 27

Rapidly propagated All-or-none Electrical message that passes along axons of the nervous system.

Question 28

Describe the depolarisation phrase of the action potential?

Answer 28

Sodium influx. -70 -\> 50mV

Question 29

Describe the depolarisation phrase of the action potential?

Answer 29

Potassium efflux. 50 -\> -70mV

Question 30

Describe the afterhyperpolarisation phrase of the action potential?

Answer 30

The sodium channels are still inactivated state therefore the cell becomes more repolarisated (-70 -\> -90mV)

Question 31

Describe subthreshold potential?

Answer 31

A graded potential starts above threshold at its initiation point but decreases in strength as it travels through the cell body. At the trigger zone, it is below threshold and therefore does not initiate an AP.

Question 32

Describe suprathreshold potential?

Answer 32

A stronger stimulus at the same point on the cell body creates a graded potential that is still above threshold by the time it reaches the trigger zone. Causes AP.

Question 33

What happens when you increase the extracellular potassium?

Answer 33

Depolarisation of the membrane potential.

Question 34

Name the two ways in which the external potassium concentration is regulated?

Answer 34

1. Blood-brain barrier. 2. Potassium spatial buffering

Question 35

How do you record a single channel voltage?

Answer 35

Patch clamp technique

Question 36

Describe the 4 different patch clamp configurations?

Answer 36

1. Cell-attached 2. Inside-out patch 3. Whole- cell recording 4. Outside-out patch

Question 37

What is the normal resting potential?

Answer 37

-65mV

Question 38

What is the chemical and electrical gradient of potassium at -65mV?

Answer 38

Outward chemical gradient \> inward electrical. Hence, potassium current is outwards.

Question 39

What is the chemical and electrical gradient of potassium at -85mV?

Answer 39

Inward electrical gradient \> outward chemical gradient Hence, potassium current is inwards.

Question 40

Name the two ways in which the ion channels are controlled in the ion movement?

Answer 40

1. Gating 2. Inactivation

Question 41

Describe channel gating?

Answer 41

Most channels spend the vast majority of time in this closed state. Requires energy to open it.

Question 42

How is gating regulated?

Answer 42

By protein conformation Independent of permeability control

Question 43

Name the two types of gating channel?

Answer 43

1. Voltage gated channels. 2. Ligand gated channels.

Question 44

Describe channel modulation when looking at gating process?

Answer 44

It is a secondary factor that alters the gating process. The ion channel only conducts certain ions but some will enter the pore but are not permeable and thus block the channel.

Question 45

What is needed to change the gate from a closed (resting) state to the open (conducting) state?

Answer 45

A change in the membrane potential.

Question 46

What are the two possible routes for an open state channel to return to the non-conducting state?

Answer 46

1. Deactivation 2. Inactivation

Question 47

Describe the deactivation state?

Answer 47

Channel return to the closed state. Driven by repolarisation.

Question 48

Describe the inactivation state?

Answer 48

Maintained depolarisation drives the gate into a different non-conducting state.

Question 49

Describe the structure of the voltage-gated ion channel?

Answer 49

4 subunit. 6 transmembrane domain in each subunit. 4th transmembrane domain is positively charged.

Question 50

How is the voltage-activated channels opened?

Answer 50

Cause of a depolarisation current. If there is a negative charge in the inside the S4 domain will be more attracted to the inside of the cell and thus opening the receptor.

Question 51

How does the voltage-activated channels go into the inactivated state?

Answer 51

Hydrophobic intracellular 'gate' between transmembrane 3 and 4 domain that binds to the intracellular mouth of the pore and inactivates it.

Question 52

IFM peptide?

Answer 52

This is the triad of amino acids that form the inactivation gate.