L3-5: Ion Channels and RMP Flashcards
What state are ion channels required to be in and why?
An open state so current can flow through the channels
How is movement in ion channels controlled?
By potential acrross the membrane and the concentration for said ion
What can ion channel gates respons to?
Stimuli such as ligands, voltage and movement
How is the tranverse tubular (t-tubule) system structured ?
Tubules are large in diameter and form an elaborate network of sarcolemma tubules, the lumen of which are continuous with the EC space
How is the sarcoplasmic reticulum (SR) structured?
It’s connected with the nuclear envelope and has an extensive network of tubules surrounding the contractile material in a tight net
What is the main function of the SR?
The sequestration of Ca2+ from the cytoplasm
The SR is differentiated into several specialised regions. One is the junctional SR, what is its role?
It forms interior couplings with t-tubules and peripheral couplings with surface sarcolemma
Define resting membrane potential (RMP)
The voltage difference between the inside and outside of the cell, caused by the movement of ion
What is ‘flux’??
The movement of ions due to difference in concentratoin across the membrane
What is the difference between hypokalamia and hyperkalamia
Hypo is too little K+ and hyper is too much K+
K+ imbalance can be caused by what?
Renal diseases and (de) hydration
What affect can K+ imbalance have on the body?
It can affect RMP and the heart’s natural rhythmn
The calculated equilibrium potential for potassium is similar to what?
The RMP of a ventricular myocyte
The current flow across a membrane is dependent upon whaat?
number of ion channels x current flow through a single ion channel x probability of the channel being open
The cell membrane carrier proteins that are described as ‘exchangers’ don’t usually require ATP as an energy source. True or false?
True
Name the 3 stages of an ECG and what they represent
P= atrial depolarisation
QRS complex= ventricular depolarisation
T= ventricular repolarisatoin
Name the 3 intervals of an ECG and what periods they represent
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
Site directed mutagenesis can be used for what?
To produce abornmal ion channels for structural investigation
- application of neurotoxins has been helpful in understanding function of ion channels
Why is knowledge of AA structure useful?
It facilitates predictions of alpha helical structures and pleated sheeets
- protein folding can be predictde & computer based modelling can be used
Alpha subunits are a key component of ion channels. Describe their strucutre
They are comprised of 6 membrane spanning alpha helical segments
Describe the structure of a typical K+ channel
Formed of 4 alpha subunits creating a tetreamer structure
What other subunit is associated with ion channels?
Beta subunits which are thought to give additional functionality to the channel e.g. affecting conduction sped
Explain the structure of the S4 alpha domain
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
Explain the affect of the selectivity filter in a K+ channel
The filter compromises 4 K+ binding sites and replaces water molecules surrounding the K+ with oxygen atoms
