Ion Channels - L2 | Flashcards

Question	Answer
What is hyperkalemia?	Raised extracellular K+
What does hyperkalemia result in?	1) Depolarises membrane 2) Activates Na+ channels 3) Na+ channels inactivate 4) Muscle paralysis
What are the different configurations an ion channel (eg Na+) can exist in? At what voltages would you expect to see this?	1) Closed, -70mV 2) Open, -50mV - +30mV 3) Inactivated, +30mV - -70mV
What cell is a two-electrode voltage clamp used on? Why? What electrodes are used?	Xenopus oocyte - very large cell Reference electrode, current electrode, voltage electrode.
What type of recording does a whole-cell voltage clamp perform? How does the cytoplasm relate to the interior of the pipette?	1) Macroscopic recording 2) Cytoplasm is continuous with interior of pipette
What can the recording pipette be used to do in a whole-cell voltage clamp?	1) Introduce channel blockers 2) Change ionic concentrations
How does a single-channel patch clamp differ to whole-cell voltage clamp? What are the different possible configurations?	1) Single or few channels recorded from 2) External or Internal membranes can be exposed
What is a more modern method of observing cell/channel activity? When is this particularly useful?	1) Fluorescence - dye changes colour with change in voltage. Fluorescence measured by photodetector. 2) Better at seeing what is happening through whole cell, can see changes in thin dendrites and axons.
What does the permeability of a cell membrane mainly depend on? What is the conductance of the cell membrane and that ion?	1) K+ 2) K+ = 80pS, CM = 100pS
What are the reversal values of Na+ and K+? Why are they rectifiers at physiological values?	1) Na+: +67mV, K+: -95mV 2) As there is little/no driving force at the reversal values and therefore no current. K+ Channels close.
How do inner hair cell currents change with maturation? What does this suggest?	Become: 1) Faster 2) Larger (from max 14nA to 19nA and +5mV/-35mV to +7mV/-45mV) 3) Do not inactivate Change in channels throughout development
What can be used to block K+ currents when dissecting whole cell currents?	TEA (tetraethylammonium)
What can be used to block Na+ currents? (2)	TTX (tetrodotoxin) or STX (Saxitoxin)
What is Ic?	Capacitance transient - 'gating current', occurs before current starts flowing, movement of charge across membrane and associated with activation of channel.
What does the shape of a single-channel recording tell you?	Width of upstroke indicates duration of time channel was open for. Double amplitude indicates two channels opening at once.
What are transient openings described in terms of?	Probability of opening, Po
What is the conductance of a Cl- channel?	30pS
Give 2 examples of channels which are gated by voltage and ligands?	1) Ik(Ca) 2) BK/maxi-K channels (Big conductance channel)
How do Ik(Ca) channels work? What are they important for and on what type of cell?	1) Ca2+ has to bind intracellularly to the K+ channel for it to become sensitive to membrane changes. 2) Important for very rapid repolarisation, don't inactivate and are found on the basolateral membrane of hair cells.
What evidence is there for the combined gating of Ik(Ca) channels?	1) Number of channels open and frequency of opening is voltage dependent (more at +80mV than -60mV) 2) Frequency of openings is dependent on concentration of Ca2+
What does the function of BK cells relate to?	Clustering of channels - Ik(Ca) and Ca2+ channels. Clustering and colocalization of Ca2+ and BK channels in hair cells.
Why do different VG K+ channels show different current traces?	Different kinetics/properties of channel
Why are many K+ channels known as 'delayed rectifiers'?	1) Delayed - slow to activate 2) Rectifier - only pass current in one direction
What are the 6 main features you might expect to see in a voltage gated ion channel?	1) Aqueous pore 2) Selectivity filter 3) Voltage sensor 4) Activation gate 5) Inactivation gate 6) Anchor protein

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Ion Channels - L2

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	Created by Anna Hogarth over 8 years ago