L3-5: Ion Channels and RMP

Question 1

What state are ion channels required to be in and why?

Answer 1

An open state so current can flow through the channels

Question 2

How is movement in ion channels controlled?

Answer 2

By potential acrross the membrane and the concentration for said ion

Question 3

What can ion channel gates respons to?

Answer 3

Stimuli such as ligands, voltage and movement

Question 4

How is the tranverse tubular (t-tubule) system structured ?

Answer 4

Tubules are large in diameter and form an elaborate network of sarcolemma tubules, the lumen of which are continuous with the EC space

Question 5

How is the sarcoplasmic reticulum (SR) structured?

Answer 5

It’s connected with the nuclear envelope and has an extensive network of tubules surrounding the contractile material in a tight net

Question 6

What is the main function of the SR?

Answer 6

The sequestration of Ca2+ from the cytoplasm

Question 7

The SR is differentiated into several specialised regions. One is the junctional SR, what is its role?

Answer 7

It forms interior couplings with t-tubules and peripheral couplings with surface sarcolemma

Question 8

Define resting membrane potential (RMP)

Answer 8

The voltage difference between the inside and outside of the cell, caused by the movement of ion

Question 9

What is ‘flux’??

Answer 9

The movement of ions due to difference in concentratoin across the membrane

Question 10

What is the difference between hypokalamia and hyperkalamia

Answer 10

Hypo is too little K+ and hyper is too much K+

Question 11

K+ imbalance can be caused by what?

Answer 11

Renal diseases and (de) hydration

Question 12

What affect can K+ imbalance have on the body?

Answer 12

It can affect RMP and the heart’s natural rhythmn

Question 13

The calculated equilibrium potential for potassium is similar to what?

Answer 13

The RMP of a ventricular myocyte

Question 14

The current flow across a membrane is dependent upon whaat?

Answer 14

number of ion channels x current flow through a single ion channel x probability of the channel being open

Question 15

The cell membrane carrier proteins that are described as ‘exchangers’ don’t usually require ATP as an energy source. True or false?

Answer 15

True

Question 16

Name the 3 stages of an ECG and what they represent

Answer 16

P= atrial depolarisation
QRS complex= ventricular depolarisation
T= ventricular repolarisatoin

Question 17

Name the 3 intervals of an ECG and what periods they represent

Answer 17

PR interval= start of P wave to start of QRS complex
QRS= start of QRS complex to the end
QT interval+ start of QRS complex to end of T wave

Question 18

Site directed mutagenesis can be used for what?

Answer 18

To produce abornmal ion channels for structural investigation
- application of neurotoxins has been helpful in understanding function of ion channels

Question 19

Why is knowledge of AA structure useful?

Answer 19

It facilitates predictions of alpha helical structures and pleated sheeets
- protein folding can be predictde & computer based modelling can be used

Question 20

Alpha subunits are a key component of ion channels. Describe their strucutre

Answer 20

They are comprised of 6 membrane spanning alpha helical segments

Question 21

Describe the structure of a typical K+ channel

Answer 21

Formed of 4 alpha subunits creating a tetreamer structure

Question 22

What other subunit is associated with ion channels?

Answer 22

Beta subunits which are thought to give additional functionality to the channel e.g. affecting conduction sped

Question 23

Explain the structure of the S4 alpha domain

Answer 23

Contains a highly conserved sequence of 6 Arg AAs

• when disrupted affects the voltage dependence of the channel
• movement of this regino in presence of changing electrical charge will lead to pulling of S5&6 segments to open the channel

Question 24

Explain the affect of the selectivity filter in a K+ channel

Answer 24

The filter compromises 4 K+ binding sites and replaces water molecules surrounding the K+ with oxygen atoms