1.1 Ion Channels And The Na/Ca Exchanger Flashcards
(42 cards)
What are the properties of ion channels?
- Ion movement is always down electrochemical gradient
- Movement is fast, 10^7 ions per second per channel
- Channels are selective
- Pore alternates between open and closed states- GATING
What is gating of a channel controlled by?
- Voltage gated- membrane potential
- Ligand gated- binding of a chemical
- Mechanical gating- membrane deformation
What is the reversal potential?
The reversal potential is the potential at which no net current flows when the channel is in its open state.
What determines the reversal potential of a ion channel?
The reversal potential depends on the relative permeability of the ion channel
how can we model the flow of ions through channels?
- Ions will only flow when the channel is open
- Ions only flow down their electrochemical gradient
Can use I=G.V or also G=1/R
An open channel can be compared to a resistor and thus we can use ohms law
However we can replace V with electrochemical gradient
With V-E rev can be found by I (pA)= Y(V-E rev)
Y= channel conductance in pS
How do we measure single channel currents experimentally?
Single channel currents can be measured using excise patches.
What are the two types patch clamp recordings?
You can have inside out patch which is where the solution in the pippet is in contact with the extra-cellular membrane while the solution in the recording chamber baths the cytoplasmic membrane.
What does a single channel i-V curve show?
Open channel current over voltage, this is different to whole cell IV plots, which are an average current over time.
What is the structure off the NCX?
The NCX exchanger is made up of 4 a repeats to form 4 ion binding sites 3 for Na+ and 1 for Ca2+
Which direction do the ions travel when NCX is operating in its forward mode?
1 Ca2+ out and 3 Na+ in
What direction do the ions flow when NCX is working in its reverse mode?
3 Na out for 1 Ca2+ in
What does reversal potential for the NCX exchanger mean?
The reversal potential is the potential at which the NCX exchanger switch’s to its reverse mode.
Why can you measure current due to the activity of NCX?
The NCX removed 1 Ca2+ for every 3 Na+ let in so there is a net movement of charge.
At typical resting potiential all of -80 mV and typical Na + conc what direction is NCX running?
Inwards?
At 0 mV (during the platue phase of cardiac cycle) what direction is the NCX running?
IDK
Why does Encx varying during an AP?
As intracellular NA and
Ca2+ is changing.
What’s do the different parts of the CV system do?
Heart- forces blood a round the body
Arterial system- Distrubutes blood and acts as a pressure reservoir
Capillaries - transfer metabolites and waste between blood and tissues.
Venous system - blood storage reservoir and return route.
What are the primary functions of the CVS
1.Carry metabolites to and waste from the tissues.
2. Communication via hormones.
3.involved in heat regulation.
4.regulates pH of ECF and osmotic balance.
What are the stages of the cardiac cycle?
1.Atrial systole- opens atrioventricular valves
2.Ventricualr systole - Isovolumetric stage all valves closed.
3. Ventricualr systole - ejection phase - atria refill semiluar valves open as blood pumped to lungs and around body.
4. Ventricualr diastole- isovolumertric phase, all valves closed.
5. Ventricular diastole- rapid refilling of ventricles
What happens to the relative durations of systole and diastole as heart rate increases
They both decrease but relative reduction of systole is much lower than that of diastole to allow for Ventricualr refilling.
What is Starlings Law of the heart?
Starlings law states that the greater the stretch of the ventricle in diastole, the greater the stoke work achieved in systole.
The energy of contraction is proportional to the initial length of the cardiac muscle fibre.
Why do cardiac myocytes operate within the acesseding phase of the length tension curve?
Cardiac muscle has a parallel elastic component which limits the sarcomere length to that of the rising portion of the length-tension curve, thins is a protein called titin.
Why is there a relationship between contractile strength and streach of the filament?
Too close then the thick filaments are compressed. Ideally in middle.
Too stretched and there is no cross bridge cycling as actin can’t reach myosin.
What happens to the proportion of cross bridges activated by at a given [Ca2+] during stretch?
More cross bridging at a given Ca2+ concentration with increasing stretch, via an unknown mechanism, although titin seems to be involved, as more complete mutant titin is causes less of a sensitivity response to Ca2+ compared to WT.
