Lecture 1 Flashcards
What is the ratio of K+ intracellularly vs Extracellularly?
20:1
What is the ratio of Na+ intracellularly vs Extracellularly?
1:9
What is the ratio of Ca2+ intracellularly vs Extracellularly?
1:10000
What does passive response mean in terms of membrane potentials?
incoming information that make the membrane potential deviate from the resting membrane potential. This could be hyper-polarization or depolarisation. This is due to incoming information from either another neuron or from a sensory stimulus.
How do ATPase Na+/K+ pumps work to establish concerntration gradient?
They are ion transporters which means that they move ions against the concentration gradient and require energy. K+ is pumped inwards and Na+ is pumped outwards in order to establish the concentration gradient. This is only one of three possible ways to establish the concentration gradient.
What does the structure of Na+/K+ pumps look like?
It has two chains. alph and beta chains.
alpha chain is the main chain that has the phosphorylation site, ATP binding site and the Na+ and K+ bind site.
Beta subunit is used for trafficking the ATPase to the right place and modulate the activity.
What are ion exchangers?
They are energy independent channels that rely on potential energy from the concentration gradient. e.g. For Na+/Ca2+ exchanger; the Na+ moves into the cell and causes a conformation change in the channel which causes Ca+ to move out the cell against its concentration gradient.
At rest, the neuronal membrane is selectively permeable to…?
K+. Potassium is close to equilibrium with little net movement due to the balance between the concentration gradient and the electrical gradient forces. This results in a membrane potential of -65mV with the interior of the neuron -65mV. Note this is close to the K+ equilibrium potential (-80mV)
What three things maintain the concentrations of neuron, inside and outside?
Energy dependent ATPase
Energy independent ion exchangers.
Permeability of K+
What is concentration gradient and electrical gradient?
The electrical gradient, is where the charge dictates where the ions should go. For example, if one side of the membrane is negative, then the electrochemical gradient would ‘pull’ positive ions to the negative side, as the positive ions are attracted to the negative environment. This will also work to depolarise the environment a bit.
The concentration gradient is the simpler one. Basically, the side of the membrane with a higher concentration of a certain molecule/ion will lose them down the concentration gradient to the side with the lower concentration of those molecules.
Does the membrane being permeable to K+ change the concentration inside of the cell?
No, look at notes for calculations. The K+ ion channel opens up at resting membrane potential because it can move out a little and reach an equilibrium where the cell is-65mV.
Explain how the voltage gated K+ ion channel is selective for K+ only?
- There is a size difference between K+ and other ions.
- K+ exist in the hydrated form in the extracullar environment and inside the channel. The ion selectivity filter makes the K+ ions line up and the top one is pushed out the cell like Newton’s cradle.
- K+ in aqueous solution is the worst comfortable form and has a certain distance to the oxygen of water.
- The amino acid chain of the ion selectivity filter has an Oxygen on the end which mimic exactly the hydrated relaxed form of K+ when its in aqueous solution. Therefore, K+ can sit within the ion filter in its most energetically relaxed form when theres a concenrtration gradient and move through easily.
How does voltage-gated, ligand gated and mechanically gated ion channels work?
- *VG:** change in conformation due to voltage change. e.g. K+ has protein structures that swivels out of the way to enable K+ to move through.
- *LG:** change in conformation due to transmitter binding. Recognise neurotransmitter or intracellular messengers. e.g Na+/K+ neurotransmitter receptor- when glutamate attached the channel opens. It is non-selective cation: no preferenece for Na+ or K+. Therefore, this is excitatory because at rest the potential for Na+ to enter is greater than K+ to leave. In this case it is not the ion itself but the conc. gradient that determine whether it’ll be excitatory or inhibitory.
- *MG:** e.g. touch- mechanically gated ion channels are deformed when e.g. things like pressure is exerted, therefore and creates a reaction in the channel.
What are inward rectifiers? outwards rectifiers?
Inward rectifiers: when in the process of a change in voltage, the ability to transmit an ion through a channel changes. i.e. an inward rectifier tend to want K+ to move inside the cell. They usually work when the cell is hyperpolarized.
Outward rectifiers are channels where in the process of K+ moving out, cell becomes more deplarized, K+ movement will change e.g. start of easy to move through the channel but become more difficult to do so.
What characteristic of a K+ ion channel is going to underline the resting potential? Which one is the leak that allows you to set the resting membrane potential?
inward rectifiers
- channel open by hyperpolarization, not open by depolarization
- open at resting potential.
