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physiology and pharma > L6 - ion channels > Flashcards

L6 - ion channels Flashcards

1
Q

what are the basic properties of ion channels?

A
  1. Gated (open and close depending on circumstances)
  2. selective permeability
  3. contain an aq pore
  4. have TMDs
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2
Q

structural requirements of an ion channel

A

a pore
a selectivity filter
a sensor ( eg voltage centre)
one or more gates

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3
Q

how many subunits does the nicotinic ACh receptor like ion channel have

A

5 (each with 4 TMDs)

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4
Q

how many a subunits does the NAChR always have?

A

2

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5
Q

how many TMDs does the NAChR channel have

which one contributes to the pore

A

4

2nd TMD of each subunit come together to line the pore

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6
Q

how many ACh (or ligands) need to bind to the NAChR channel and where do they bind

A

2x ACh bind to the alpha subunit

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7
Q

how many subunits does the VG Na channel have?

A

one large subunit

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8
Q

where are the C and N terminal of the VG Na channel located

A

intracellular

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9
Q

describe structure of the VG Na channel

TMDs and pore

A

4 repeating sections of 6 TMDs

the 4th TMD of each domain (6 in total) is the voltage sensor

there is a P loop between TMDs 5&6 of each domain which form the pore

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10
Q

what is the voltage sensor on the VG Na channel? and how does it work

A

the 4th TMD on each of the 6 domains

it contains charged AAs which move in response to voltage changes which can open the channel

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11
Q

what are subunits?

A

individual proteins which may have several TMDs

so the Ca and K channels are formed of many separate proteins whereas the Na channel is one single protein

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12
Q

how many subunits does the VG K channel have

A

4

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13
Q

how many TMDs does each of the subunits of the VG K channel have

and which one contributes to the

  • pore
  • voltage sensor
A

6

P loop contributes to pore

TMD 4 is the voltage sensor

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14
Q

what is the equilibrium potential (E) of K

A

-90mV

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15
Q

what is the equilibrium potential (E) of Na

A

+60mV

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16
Q

what is the equilibrium potential (E) of Cl

A

-70mV

17
Q

what is the equilibrium potential (E) of Ca

A

+130mV

18
Q

define electrochemical driving force

A

voltage that pushes the ions through the channel

the difference between the membrane potential and the equilibrium potential for that ion
Vm - E(ion)

19
Q

what does a negative Em / Vm (both mean membrane potential) mean

A

inside the cell is more negative than the outside

20
Q

at a Vm of -60mV, what is the electrochemical driving force for K

A

(-60) - (-90) = +30

21
Q

what does it mean if the electrochemical driving force is
+
-

A

if its + ions flow out of cell

if its - ions flow into cell

22
Q

what is the threshold for opening of VGCCs

A

-30mV

23
Q

what is the reversal potential?

A

the membrane potential at which the flow of K+ out and Na+ in cancel eachother out

24
Q

what would the reversal potential of a non selective Na and K channel be if t was equally permeable to both?

A

half way between the E(Na) and E(K)

-15mV

25
Q

what is the usual reversal potential for non selective Na K channels and why is this the value

A

approximately 0mV

channel is slightly more permeable to Na than K

26
Q

what is the threshold for opening of VG Na channels

A

-55mV (same as AP threshold)

27
Q

what are the 3 ways ion channels can be classified based on their physiological properties

A
  1. Gating mechanism
    eg voltage gated, ligand gated, temperature gated, [Ca]/[ATP] gated
  2. ion selectivity
    eg Na channel, non-selective cation channel
  3. kinetics
    eg fact activating, slowly inactivating, transient
28
Q

what other ways can channels be classified

A
  1. based on their pharmacology
    eg what channels are blocked/ opened by certain drugs
  2. based on their structure
    eg sodium channel, K channel, nAChR, P2Y channels etc

physiology and pharma (18 decks)

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