Ion channels

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How can ion channels be distinguished from transporters
Higher ion transport rates, and their behaviour can be predicted by the nernst equation. They show distinct gating characteristics
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When we look at voltage clamped ionic currents, what are we really looking at
the average of all the activities of all the single channels in the cell
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How can we classify ion channels
By their physiology - gating, ionic selectivity and kinetics.
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Examples of different gating properties
voltage, ligand, ion, mechanical, thermal, metabolic factors
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Examples of ion that channels can be selective for
Na, Ca2+, K+, Cl-, any ion, any monovalent cation, any cation
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Examples of kinetics that can be used to classify ion channels
fast acting, slow acting, transient, sustained.
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What are the channels underlying the upstroke of the AP
voltage gated, Na+ selective channels, fast activating transient channels.
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What channels underly the downstroke of the AP
voltage gated K+ selective channels that activate relatively slowly and remain open
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What kind of ion channel is the nicotinic receptor
a endogenous ligand (Ach) gated non specific monovalent cation channel, opens quickly but transiently
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Are vg channels only voltage dependant?
No, sometimes they have ligand binding sites, like VG sodium channels can be activated by veratridine
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Why doesn't the NMDA receptor show a linear relationship between Vm and glu-induced current
the Mg2+ block is removed in a voltage dependant way
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How can we tell if a drug activates a Cl- channel
The reversal potential will be equal to the equlibrium potential for that ion
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Another way we can classify ion channels
by pharmacology - by the effects of channel blockers, channel openers, and channel modulators.
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Example of how we classify Voltage gated Na+ channels by pharmacology
tetrodotoxin sensitive Na channels and ttx-insensitive voltage gated sodium channels
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Example of how we classify Voltage gated K+ channels by pharmacology
Tetraethylammonium blocks most but not all voltage-gated K+ channels - TEA sensative and TEA insensitive.
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What ion selectivity do voltage gated channels often show
high specificity for a single ionic species
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Most classes of ligand-gated ion channels show what kind of ion selectivity
non-specific cation channels that conduct any monovalent positive ion, often limited by size, Sometimes divalent ions particualrly Ca2+
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What kind of receptor is the ryanodine receptor
calcium activated ca2+ channel.
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What kind of ion channels are ASICs - acid sensing ion channels
non-selective cation channels
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Describe the structure of the voltage gated sodium channel
single polypeptide of 2000 amino acids. 4 homologous domains with 6 tm alpha helixes, and a P loop. the 4th TM a helix in each domain is a voltage sensor.
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How many genes encode voltage gated sodium channels
At least 9, maybe 10
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Describe the structure of the voltage gated potassium channel
single polypeptide that has 6 tm spanning a-helices and a P loop,. Forms a tetramer in the membrane.
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How many families of K channels are there
at least 9
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Card 2

Front

When we look at voltage clamped ionic currents, what are we really looking at

Back

the average of all the activities of all the single channels in the cell

Card 3

Front

How can we classify ion channels

Back

Preview of the front of card 3

Card 4

Front

Examples of different gating properties

Back

Preview of the front of card 4

Card 5

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Examples of ion that channels can be selective for

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