4971671
Beschreibung
Karteikarten von Anna Hogarth, aktualisiert more than 1 year ago
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Erstellt von Anna Hogarth
vor mehr als 8 Jahre
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| Frage | Antworten |
| 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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