ICPP 4 Flashcards
What is the effect of caffeine on drugs?
It increases blood flow and heart rate which increases efficacy of drugs
Define membrane potential.
The magnitude of electrical charge that exists across a plasma membrane, expressed as the potential inside the cell relative to the EC solution.
All cells have a ______ resting membrane potential.
negative
There are 2 important factors essential for membrane potential to be established, what are they?
- Asymmetric distribution of ions across membrane
2. Selective ion channels in the plasma membrane
What are the 3 ions which are most important in membrane potential?
K+, Na+ and Cl-.
K+ moves in which direction, what does this lead to?
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.
Why will K+ want to move back into the cell,against its chemical gradient?
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.
Which channels dominate the membrane at rest?
Open K+ channels
What is the nernst equation used to calculate?
The membrane potential of an ion, given the intracellular and extracellular concentrations.
Which ions contribute to the membrane potential of around -70mV?
Na+,K+ and Ca2+
Na+ and Ca2+ both have a ________ equilibrium potential.
Positive.
K+ has a negative equilibrium potential. If the membrane was permeable this ion alone, membrane potential would be….
-95mV
Not all cells have a rmp of -70mV, why is this?
Increased contribution from other ions, less K+ selective.
Cardiac muscle and nerve cells are more selective to K+, how is this reflected in their membrane potential?
Their mp is closer to the K+ equilibrium potential
What is depolarisation?
A decrease in the size of the membrane potential from its normal value.
Interior becomes less negative.
What is hyperpolarisation?
An increase in the size of the membrane potential, cell interior becomes more negative.
Increasing the membrane permeability to a particular ion will move the membrane potential towards what? Give an example.
Towards the equilibrium potential for that ion.
E.g in depolarisation when membrane becomes more permeable to Na+, the membrane potential rises towards ENa+.
The opening of which channels will cause hyperpolarisation?
K+ and Cl-, as these both have negative eq. Potentials.
The opening of which channels will cause depolarisation?
Na+ and Ca2+ as they both have positive equilibrium potentials.
Which equation takes into account the contribution of more than one ion?
GHK
Define conductance.
How permeable a membrane is to an ion
Give an example of a less selective channel.
nACh receptor is a cation channel, lets both Na+ and K+ through.
Where is an example of mechanical gating?
Hair cells in the inner ear
What types of receptors are involved in fast transmission?
Receptor protein is also an ion channel, transmitter binding causes immediate opening.
What do inhibitory transmitters cause?
Hyperpolarisation .. prevent action potential from firing.
What are the 2 patterns associated with slow synaptic transmission?
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
Give an example of an electrogenic pump.
Na+/K+ ATPase. Net loss of one positive charge each time.
How does a beta-cell secrete insulin?
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.
How do sulphonylurea’s act to treat type 2 diabetes?
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.
Outline the 4 stages of the cardiac action potential.
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.
What are the properties of cardiac ion channels?
- Only permeable to ONE type of ion
- Time -dependence - some ion channels close a fraction of a section after opening (fast Na+ channels)
- Voltage-sensitive gating - specific channels open and close in a small MP range.
Define equilibrium potential.
For each ion, the equilibrium potential is the membrane potential where the net flow through any open channel is 0.
How would you measure the membrane potential?
using a microelectrode
