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Neuroscience - Unit 5 > Lecture 4 - Transporters - Channels > Flashcards

Lecture 4 - Transporters - Channels Flashcards

1
Q

What did the voltage clamp experiments by Hodgkin and Huxley predict?

A

1) Separate Na and K channels 2) Voltage sensors in channels 3) high conductance of channels to specific ions

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2
Q

What helped form Hodgkin and Huxley’s predictions?

A

voltage clamp experiment indicating how Na+ and K+ currents change with increasing

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3
Q

What happens once the patch clamp voltage reaches +52 mV?

A

that the early inward Na+ current is missing

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4
Q

In the voltage clamp experiment, what happens at +65 mV?

A

it reverses to an outward flow.

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5
Q

What happens as the voltage becomes more and more positive?

A

the later outward K+ current increases in magnitude

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6
Q

What does the path-clamp technique allow for?

A

It allows for characterization of single channels

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7
Q

Patch-clamp is

A

a refinement of the voltage-clamp technique where voltage change activates channel openings.

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8
Q

Who developed the patch clamp?

A

developed by Sackman and Neher (Nobel Prize winners).

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9
Q

What is the patch-clamp technique?

A

Glass pipette is pressed against a cell membrane – slight suction is applied to generate a ‘gigaseal’ (low noise).

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10
Q

What is the purpose of the gigaseal?

A

All current flows through electrode and does not leak through the seal.

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11
Q

Describe the current in the patch clamp technique?

A

1) Macroscopic currents ~10-100 picoAmps (pAs) due to current flow through many channels 2) Microscopic current amplitude ~fraction of pA to several pAs due to current flow through one channel (lower right panel).

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12
Q

What is the macroscopic current flow due to?

A

Current flow through many channels

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13
Q

What is the microscopic current flow due to?

A

Current flow through one channel

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14
Q

Patch clamp recordings

A

it detects current flowing through single membrane channels due to depolarization

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15
Q

Describe the channels in the patch clamp experiment.

A

1) channels open and close in an all or none fashion 2) there is fast switch between open and close states 3) channels open and close in stochastic (random) manner

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16
Q

In the patch clamp experiment, what does gating refer to?

A

1) Gating is the transition between open and closed states 2) gating involves a temporary conformational change in the channels structure

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17
Q

In the patch clamp, what happens in response to the depolarizing effect from the pipette?

A

single channels open and close in an all or none fashion. Random or stochastic in nature

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18
Q

In patch clamp, what does the probability of opening depend on?

A

The stimulus; 1) voltage change or 2) ligand binding

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19
Q

What does the patch clamp measurements of ionic currents through single Na channels reveal?

A

1) voltage gated Na channels 2) depolarization increases the probability of a channel being open and hyperpolarizing decreases it

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20
Q

Depolarizing stimulus

A

increases the probability that the Na+ channel is opened.

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21
Q

The greater the depolarization

A

the higher the probability of channel opening.

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22
Q

For patch clamp looking at Na channels what happens to K+ channels?

A

they were blocked in this experiment to look at Na channels. Therapeutic drugs that act on ion channels are now being tested using this technique.

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23
Q

What is the patch clamp measurements of inward ionic currents through single Na channels vs the cell?

A

Macroscopic current arises from the aggregate effects of 1000s of microscopic currents (individual channels)

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24
Q

Stimulus (membrane potential depolarization of patch)

A

changes the probability that channel is open or closed.

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25
Q

Comparing the time course of the macroscopic current and the sum of many trials of the single ion channel show what?

A

close correlations of time courses of the macroscopic and microscopic currents

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26
Q

Is channel opening controlled in the patch clamp experiment?

A

Random or stochastic opening of channels

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27
Q

Probability of opening

A

increases with depolarization

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28
Q

Microscopic current

A

single channel

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29
Q

Macroscopic current

A

summed activity of 1000s of Na+ channels (K+ channels blocked).

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30
Q

Compare the Na and K channel data from the patch clamp experiment.

A

opposite current direction, longer latency for activation and long duration of activation for the K+ channel vs the Na+ channel properties.

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31
Q

The sum of many microscopic trials approximates what?

A

the time course of the macroscopic currents from the whole cell.

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32
Q

Sustained response (patch clamp)

A

on average the K+ channels tend to be an open state while the membrane is depolarized.

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33
Q

K+ channels diversity.

A

Multiple types of voltage gated K+ channels exist that have different properties and influence neuron firing.

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34
Q

Microscopic and macroscopic currents

A

Properties of microscopic currents (patch clamp) are the same as those of macroscopic currents

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35
Q

Na channels

A

1) opening is voltage dependant 2) opening near beginning of depolarization pulse 3) inactivate 4) current reverses at Na equilibrium potential 5) TTX blocks

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36
Q

K channels

A

1) opening is voltage-dependant 2) opens later 3) many do not inactivate, they just close 4) TEA or (Cs) blocks it

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37
Q

K channels in the CNS

A

most CNS neurons have multiple Potassium channels with different characteristics

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38
Q

K channel diversity as it pertains to voltage

A

voltage dependence of activation (low voltage versus high voltage activation)

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39
Q

K channel diversity as it pertains to rate?

A

Diversity in the rate of activation (How fast the population reaches maximum conductance)

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40
Q

K channel diversity as it pertains to inactivation

A

inactivation properties, some inactivate quickly, some inactivate slowly, some don’t inactivate, this produces a diversity of spike waveforms and spike patterns for different cells

41
Q

Functional roles of the after hyperpolarization

A

1) Fast AHP 2) Medium AHP 3) Slow AHP

42
Q

Fast AHP

A

1) (2-5 ms) shortens the AP by quickly repolarizing the membrane. 2) Only affects early spike frequency at very high frequencies 3) BK K channels, activation by Ca and depolarization and then rapid inactivation

43
Q

Medium AHP

A

1) (10-100 ms) controls early interspike interval 2) contributes to early spike frequency adaptation, slowly activating by Ca entry 3) controls late spike frequency adaptation (IK and SK, K channels, non inactivating)

44
Q

Slow AHP

A

(100ms – 3000ms) Limits firing frequency by an unknown channel

45
Q

For the functional roles of AHP, which are rapid inactivation and which are non-inactivating?

A

1) Fast AHP = rapid inactivation 2) Medium AHP = non-inactivating

46
Q

In some types of neurons what is the role of voltage gated Ca channels?

A

They result in bursts of APs that may last 100ms or longer

47
Q

Channel timings

A

1) Na channels open 2) Na channels inactivate, Ka+ and Kdr+ channels open 3) Kbk+ channels open 4) Ca channels open 5) other known and unknown K+ channels open

48
Q

What results in neurons with diverse electrical properties?

A

Larger number of ion channel genes

49
Q

Voltage gated channels typically

A

allow only a single type of ion to pass through the channel although there are exceptions.

50
Q

Ligand gated ion channels often

A

allow two or more types of ions to pass through the channel.

51
Q

Ionic channels are organized based on

A

sequence homology

52
Q

Voltage dependant ion channels differ in

A

their cellular expression and subcellular localization impacting their relative contribution to brain function

53
Q

Kv4.1

A

these channels play a positive role in tumorigenic human mammary cells.

54
Q

What does double immunofluorescence staining for Kv1.4 and Kv2.1 in the adult hippocampus show?

A

1) Staining for Kv1.4 is red and are axons 2) Staining for Kv2.1 is green and are soma proximal dendrites

55
Q

In adult hippocampus, Kv1.4 staining?

A

In terminal fields of the medial perforant path in the middle molecular layer of the dentate gyrus and mossy fiber axons and terminal s. lucidum of CA-3

56
Q

In adult hippocampus, Kv2.1 staining?

A

It is most prominent in the pyramidal cell CA-1 layer

57
Q

Why are there so many genes encoding K+ channels?

A

So the genes can differ in: 1) activation 2) gating 3) inactivation

58
Q

What does the diversity of K channels allow?

A

Influence the duration of AP and resting membrane potential

59
Q

The Kv2.1 channels

A

show little inactivation and are related to channels involved in repolarization.

60
Q

The Kv4.1 channels

A

inactivate rapidly to depolarization.

61
Q

The inward rectifier channels

A

allow more current flow during hyperpolarization than during depolarization.

62
Q

The Ca++ activated K+ channel

A

opens in response to increased intracellular Ca++ and sometimes to membrane depolarization.

63
Q

Ion channels encoded by

A

large and diverse families of homologous genes

64
Q

Ion channel differences

A

they differ widely in cellular expression and subcellular localization

65
Q

Voltage gated channel differences

A

different voltage gated channels differ in functional properties (activation, inactivation and gating)

66
Q

Ion channels contribute to

A

rich electrical responses

67
Q

Ion channel diversity

A

is key to developing new therapeutics for central nervous system disorders

68
Q

Channelopathies

A

they are genetic diseases resulting from mutations in channel genes

69
Q

Channelopathies, voltage gated Ca channels

A

1) congenital stationary night blindness 2) familial hemiplegic membrane 3) episodic ataxia type 2

70
Q

Channelopathies, Na channel defect

A

generalized epilepsy with febrile seizures

71
Q

Channelopathies, K channel mutations

A

benign familial neonatal convulsion

72
Q

Toxins target what sites on ion channels

A

extracellular domains and pore regions

73
Q

Tetrodotoxin

A

(puffer fish) block Na channels

74
Q

Saxitoxin

A

(red tide) a homologue of TTX

75
Q

Alpha toxins

A

(scorpion) prolong duration of Na currents

76
Q

Beta toxins

A

(scorpion) shift voltage activation of Na channels

77
Q

Batrachotoxin

A

(frogs) inactivation of Na channels (used by South American indians)

78
Q

Dentrotoxin

A

(wasps) K+ channel blockers

79
Q

Amapin

A

(bees) ?

80
Q

Omega – conotoxins

A

(cone snails) – N-type Ca channels

81
Q

Omega – agatoxin

A

(spiders) P/Q – type Ca channels

82
Q

Active ion transporters are

A

membrane proteins that create and maintain ion gradient

83
Q

Active ion transporters that translocate what?

A

Translocate ions against their electrochemical gradient (consume energy)

84
Q

Active ion transporters form what?

A

Form complex with ion they transport

85
Q

Active transport; binding and unbinding

A

is slow (ms)

86
Q

Active transport versus channels

A

ion translocation is slower in transporters than in channels (1000/sec)

87
Q

ATPase pumps (Na/K, Ca)

A

acquire energy from hydrolysis of ATP

88
Q

Ion exchangers and co-transporters

A

depend on the electrochemical gradient of other ions as other sources

89
Q

Ion exchangers

A

trade an intracellular ion for an extracellular ion, e.g., Na/Ca, Na/H and do not use ATP as an energy source.

90
Q

Ion co-transporters

A

transport two or more ions/molecules in the same direction across the membrane.

91
Q

Ion channels regulate

A

the flow of ions across the membrane, influencing cell activities

92
Q

Channels differ in

A

ion selectivity and in factors that control their gating

93
Q

Ion selectivity

A

is achieved through interactions between the ion and the amino acids that line the walls of the channel pore (selectivity filter)

94
Q

Patch clamp technique

A

measure current flow through single open channels

95
Q

Gene cloning

A

determine the sequence of genes that encode channels

96
Q

X-ray crystallography

A

provided detailed 3D structure of the bacterial K channel

97
Q

Channels are targets of

A

blockers, toxins, and various diseases resulting from genetic mutations

98
Q

Active ion transporters are

A

membrane proteins that create and maintain ion gradients using ATP as the energy source

99
Q

Ion exchangers

A

use the electrochemical gradients of co-transported ions as an energy source to exchange ions

Neuroscience - Unit 5 (12 decks)

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