- Created by: 11APhillips
- Created on: 31-12-19 11:35
- This is a way of recording from neurons without destroying the cell
- A patch pippette forms a high resistance giga-ohm seal with the cell, creating an on cell patch.
- Negative pressure is then used to **** a bit of the membrane into the pippette, with the inside facing outward, creating an inside out patch. Good for studying 2nd messenger systems.
- Outside out is made from a whole cell clamp and is the reverse it is good for studying ion channels.
Cell-attached patch recordings
- A type of patch clamping.
- Quick inward current characteristic of an Na channel, slow outward current characteristic of a K+ channel.
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Na and K channels
- Na channels open, and then are inactivated using the inactivation gate, before properly closing.
- K+ channels only have open and closed states.
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- A gating current is the small current that moves across voltage gated channels upon voltage application
- It is so small that it can only be detected by removing the usual currents that the channel produces using TTX to stop Na channels, or caesium to stop K channels.
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Different types of ion channels
- The two main types are voltage gated and ligand gated.
- Voltage gated channels include Na, K, and Ca channels.
- Ligand gated include the glutamate receptors.
- These are opened by both voltage and intracellular Ca, a combination fo which gives the largest opening.
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The structure and function of ion channels
- Four repeats of six transmembrane domains.
- The alpha subunit contains the pore (has the four repeats).
- TTX binds to sodium channels, but Glutamate->glycine stops this interaction (between s5 and s6 of repeat 1).
- A ring of negative charge is how the channel selects for posivie charge
- S4 is the voltage sensor and has lots of positively charged residues
- It is an alpha helix and membrane potential changes induce conformational changes in it
- When you reduce the positive charge of S4, the gating current is reduced.
- 4 proteins of six transmembrane domains, which can be heteromultimeric.
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Inactivation of Sodium channels
- Follows the hinged lid model.
- It uses isoleucine, phenylalanine and methionine between repeats 3 and 4
- They form a lid to inactivate the channel
- If you remove the phenylalanine, the channel cannot be inactivated, and shows behaviour more like potassium channels.
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- It exhibits dominant inheritence and causes muscle stiffness preceded by paralysis
- S4 of repeat 4 is mutated, which usually couples activation with inactivation
Hyperkalemic periodic paralysis
- Once again, attacks of muscle weakness triggered by heightend blood potassium levels (4 to 5 mM).
- Incomplete inactivation of the Na channel
- Aggravated by potassium rich food
- Mutations in the inactivation loop, whereby a glycine is replaced by a glutamate
- Causes a slower closure of Na currents.
- The presence or absence of paralysis depends on the fraction of Na current that doesn't turn off
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