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Cell Physiology & Pharmacology > Membrane Potential > Flashcards

Membrane Potential Flashcards

1
Q

What is a P-type ATPase?

A

An ion channel that hydrolysed ATP to move the ion, forming an phosphoenzyme intermediate

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2
Q

What is approximately the resting membrane potential of a cell?

A

-70mV

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3
Q

What is mainly responsible for maintaining a resting membrane potential of -70mV?

A

The diffusion of K+ ions out of the cell

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4
Q

How would you define a symporter ion channel?

A

An ion channel that transports 2 different types of ion in the same direction

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5
Q

By which mechanism does a secondary active transporter function?

A

A secondary active transporter transports its ion(s) using the energy of an electrochemical gradient, as opposed to the hydrolysation of ATP in primary active transport

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6
Q

What 2 factors does the Na+ H+ Exchanger regulate in a cell? Explain how.

A

The Na+ H+ Exchanger regulates pH, via the removal of H+ ions from within the cell.
It’s also regulates cell volume, by pumping Na+ ions into the cell - water follows these ions into the cell down the concentration gradient that the Na+ ion movement creates.

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7
Q

Although indirectly, what ion transporter plays a major role in the maintenance of a cells pH?

A

The Na+ K+ ATPase pump

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8
Q

What 3 osmotically ‘active’ ions play a key role in the movement of water through a cell? How does water react to their movement?

A

Na+, K+, and Cl-

In general,Mayer follows these ions in/out of the cell

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9
Q

Do animal cells have a positive or negative resting membrane potential?

A

Negative

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10
Q

Define the membrane potential.

A

The magnitude of electrical charge across a plasma membrane

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11
Q

State the 2 main factors that are crucial in maintaining a membrane potential

A

Asymmetric distribution of ions across a membrane

Selective permeability

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12
Q

Are K+ ion concentrations higher inside or outside the cell?

A

Inside

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13
Q

Are cations positively or negatively charged?

A

Positively charged ions

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14
Q

What type of molecules is the lipid bilayer of the plasma membrane permeable to?

A

Small uncharged molecules

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15
Q

What equation is used to work out the chemical,gradient of an ion?

A

RTln( (X)out / (X)in )

R = gas constant 
T = temperature in Kelvin
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16
Q

At equilibrium, what are the chemical and electrical gradient in regards to one another?

A

In balance

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17
Q

What is the Nernst Equation used to calculate?

A

The resting membrane potential at which a specific ion will be in equilibrium (an ions concentration and electrical gradient will be in equilibrium)

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18
Q

Which ion in particular plays the most prominent role in maintaining the resting membrane potential?

A

K+ ions

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19
Q

Will an ion prefer to move down its chemical or electrical gradient first?

A

An ion will move down its chemical gradient before its electrical gradient

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20
Q

What are the equilibrium potentials for Na, K, Cl, and Ca?

A 
Na = 70mv
K = -95mv
Cl = -96mv
Ca = 122mv
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21
Q

What is depolarisation?

A

Depolarisation is where the membrane potential of the cell decreases, causing the interior of the cell to become more positive

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22
Q

What is the Golman-Hodgkin-Katz equation used to work out?

A

It is used to work out the membrane potential of a cell based on its permeability to Na, K, and Cl

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23
Q

What is hyperpolarisation?

A

An increase in the size of the membrane potential, where the interior of the cell becomes more negative

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24
Q

How many acetylcholine molecules must bind a nicotinic acetylcholine receptor for it to open? What will this then allow through?

A

2 acetylcholine molecules must bind the receptor for it to open - it will let through cations (namely Na and K)

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25
Q

Concerning ion channels, how many ways of ‘gating’ are there? What are they?

A

3 ways

  • ligand gated
  • voltage gated
  • mechanical gated
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26
Q

List 2 inhibitory neurotransmitters. How do they act?

A

Glycine and GABA - they act by opening anion ligand-gated channels which allow K and Cl to enter the cell - this causes hyperpolarisation, meaning the cell will not be able to fire an action potential

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27
Q

In the Goldman-Hodgkin-Katz equation, which ion has an opposite orientation to the other?

A

Cl (in/out)

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28
Q

How does opening a nicotinic acetylcholine receptor affect the membrane potential of a cell?

A

It lets in cations, particularly Na and K, moving the membrane potential towards 0mv (an intermediate between the membrane potentials of Na and K)

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29
Q

List 3 excitatory neurotransmitters. What do they cause?

A

Acetylcholine, glutamate, and dopamine - they cause depolarisation of the cell via influx of ions such as Na or Ca

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30
Q

Where might synaptic transmission be slow? Where might it be fast?

A

Synaptic transmission may be slow when the initial receptor and eventual ion channel are seperate proteins - synaptic transmission will obviously quicker if the receptor protein is also an ion channel

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31
Q

What is the resting membrane potential of a cardiomyocyte?

A

-90mv

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32
Q

Explain the mechanism of an action potential in cardiomyocytes.

A
  • initially, fast-acting Na channels begin opening, causing the cell to depolarise
  • as membrane potential reaches -70mv there is a surge of Na influx
  • this rapid influx causes depolarisation to 0mv
  • L-type Ca channels open when membrane potential reaches -40mv
  • K channels open, causing these cations to leave the cell which leads to repolarisation (as positive charges are leaving)
  • delayed rectifier K channels remain open and propagate the expulsion of further K from the cell, hyperpolarising it
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33
Q

What is the name of the equation given to calculate the membrane potential of a single ion?

A

The Nernst Equation

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34
Q

What is responsible for the unequal distribution of ions between the intracellular and extracellular fluid?

A

Ion transporters

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35
Q

How can you measure membrane potential?

A

Using a microelectrode (which is really thin as to not cause the cell to burst) attached to a voltmeter - the microelectrode will be filled with a conducting solution (KCl)

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36
Q

What happens to the membrane potential when K ions leave?

A

It hyperpolarises

37
Q

What is the Nernst equation (with constants at room temperature)?

A

E = 61/Z log10(ion out / ion in)

Z = valency

38
Q

In which direction does Ca flow in a myocytes when it undergoes an action potential?

A

It flows intracellularly

39
Q

What happens to the membrane potential when Na ions enter?

A

The membrane potential depolarises

40
Q

Do action potentials propagate with or without a decrease in amplitude?

A

They propagate without a decrease in amplitude

41
Q

If a cells permeability to a specific ion is increased, how will this ion act in the cells membrane potential?

A

The ion will act to reach its own equilibrium potential, and will act on the membrane potential in whatever manner to get closer to its own equilibrium potential

42
Q

How can you show experimentally that Na+ is responsible for the initiation of an action potential?

A

The peak of an action potential changes in a manner parallel to the changes seen when Na+ attempts to reach is equilibrium potential - therefore the upstroke of an action potential is due to a large increase in a permeability to Na+ ions

43
Q

Do you need a large influx of ions to generate an action potential?

A

No

44
Q

How do K+ channels act in comparison to Na+ channels?

A

K+ channels open more slowly (causing repolarisation) and also close more slowing (leading to hyperpolarisation) in comparison to Na+ channels

45
Q

Does the Na K ATPase pump influence repolarisation of a cell?

A

No

46
Q

Are Na+ channels inactivated or closed in the absolute refractory period?

A

They are inactivated, and as such cannot generate an action potential

47
Q

Describe that state of Na+ channels in the relative refractory period.

A

They are recovering from inactivation and beginning to close - therefore if a stimulus is great enough some channels may be able to propagate an action potential

48
Q

What region of the Na+ and K+ channels contain positive amino acid residues? What is their function?

A

The S4 region - these positive residues contribute to voltage sensitivity

49
Q

How does an action potential induce a conformational change in a voltage-gated channel?

A

The voltage-gated channel is surrounded by a voltage field - an action potential will cause a change in this field, and have a different effect on the charges of the voltage-gated channel - this different force on the amino acids causes them to undergo a conformational change

50
Q

Concerning myelinated axons, which order do local anaesthetics block them?

A

1 - small myelinated axons
2 - unmyelinated axons
3 - large myelinated axons

51
Q

Generally, what is the mechanism of local anaesthetics? Give an example.

A

Generally, local anaesthetics block Na+ channels - an example is procaine

52
Q

What is membrane resistance dependent on? Therefore, what would produce a low membrane resistance?

A

Membrane resistance is dependent on the number of open ion channels - if there is a low membrane resistance, there will be many open ion channels

53
Q

Define capacitance.

A

The ability to store charge

54
Q

In terms of resistance and capacitance, what can increase the spread of local membrane resistance?

A

High membrane resistance, and a low membrane capacitance

55
Q

How does increasing resistance increase local spread?

A

More channels are closed, so the charge is kept inside and can propagate further

56
Q

How does a myelin sheath work?

A

Myelin sheaths act as good insulators, therefore local currents can depolarise adjacent Nodes of Ranvier much more easily

57
Q

How does a myelin sheath increase conductivity?

A

Increases membrane resistance

Decreases membrane capacitance

58
Q

What is the most common demyelinating disorder?

A

Multiple sclerosis

59
Q

How does demyelination result in poor transmission of an action potential?

A

There are no Na+ channels directly under a myelin sheath - as this has been broken down, it can no longer insulate local currents, and an action potential cannot propagate as there are no voltage-gated Na+ channels

60
Q

State the extracellular concentrations of Na+, K+, Ca+, and Cl-.

A
  • Na+ = 145 mM
  • K+ = 4 mM
  • Cl- = 123 mM
  • Ca2+ = 1-2 mM
61
Q

State the intracellular concentrations of Na+, K+, Ca+, and Cl-.

A
  • Na+ = 12 mM
  • K+ = 155 mM
  • Cl- = 4.2 mM
  • Ca2+ = 10^-7 M
62
Q

What percent of body weight can be attributed to water? How much water is therefore in a 70Kg female?

A

Water is responsible for 60% of an individual’s body weight

- 60% of 70 = 70 X 0.6 = 42 litres

63
Q

What proportion of body fluid is intracellular and extracellular?

A

1/3 is extracellular - 2/3 is intracellular

64
Q

What compartments comprise the extracellular fluids? What is their volumes?

A

The interstitial fluid (11 litres) and blood plasma (3 litres)

65
Q

What ion is most greatly associated with the movement of water?

A

Na+ ions

66
Q

What would be the consequence of vessels being permeable to plasma proteins?

A

Plasma proteins would move out of the blood vessels into the interstitial spaces - water would follow these plasma proteins down a concentration gradient, leading to oedema on a mass scale

67
Q

How do intracellular concentrations of K+ compare to extracellular concentrations? Use appropriate figures.

A

Intracellular concentrations of K+ (155 mM) are much greater than extracellular concentrations (4 mM)

68
Q

How do intracellular concentrations of Na+ compare to extracellular concentrations? Use appropriate figures.

A

Intracellular concentrations of Na+ (12 mM) are much lower than extracellular concentrations (145 mM)

69
Q

How do intracellular concentrations of Ca2+ compare to extracellular concentrations? Use appropriate figures.

A

Intracellular concentrations of Ca2+ (10^-7 M) are much lower than extracellular concentrations (1 mM)

70
Q

How do intracellular concentrations of Cl- compare to extracellular concentrations? Use appropriate figures.

A

Intracellular concentrations of Cl- (4.2 mM) are much lower than extracellular concentrations (123 mM)

71
Q

What does all-or-nothing mean?

A

A threshold is needed to be met before an action potential is induced - if this threshold is not met, no action potential can form

72
Q

What is meant by the terms activation and inactivation, in regards to voltage-gated ion channels?

A

Activation relates to when the threshold of a voltage-gated ion channel is met - inactivation relates to the period after activation, where the voltage-gated ion channels are in recovery

73
Q

What is the absolute refractory period?

A

This is the period directly after an action potential where no action potential can be generated

74
Q

What is the relative refractory period?

A

The period after the absolute refractory period where some Na+ receptors are just becoming active again, and so can be stimulated again to reach threshold and instigate another action potential

75
Q

How do local anaesthetics act to block action potentials at peripheral nerves?

A

They block action potentials by blocking the entry of Na+ into the cell by blocking Na+ channels

76
Q

Describe the mechanism behind a drug that acts as a depolarising blocker.

A

These type of drugs ensure the membrane remains depolarised, so another action cannot form

77
Q

How does acetylcholine release result in an action potential at a skeletal muscle fibre?

A

Acetylcholine binds to a nicotinic muscle receptor at a neuromuscular junction - this instigates HAVE A LOOK

78
Q

What is responsible for the unequal distribution of inorganic ions between the intracellular and extracellular fluid?

A

Ion channels and transporters

79
Q

Given the concentration gradient that is set up, in which direction would you expect K+ ions to move?

A

To the extracellular space, outside the cell

80
Q

Why is the membrane potential not parallel to any one ion acting on its membrane?

A

Due to the electrical influence of all the other ions that are having an influence on the cellular membrane

81
Q

What equation is used to measure an ions resting membrane potential? Write it out.

A

The Nernst equation - E[ion] = RT/ZF Log([ion out / ion in])

82
Q

What is the Nernst equation measured in?

A

Millivolts (mV)

83
Q

How is glucose transferred from the gut lumen into the bloodstream?

A

Glucose is taken into the cell via SGLT1, a symporter than facilitates the transfer of Na+ and glucose into the cell - from here, glucose is transferred into the bloodstream by a GLUT2 uniporter

84
Q

What type of transport transfers glucose from the gut lumen into the cells of the gut wall? Does this require energy?

A

Symport, with a Na+ molecule - this is secondary active transport as the Na+, K+, ATPase uses ATP to move Na+’out of the cell and set up a Na+ concentration gradient

85
Q

How does insulin stimulate the uptake of glucose in adipose and skeletal muscle cells?

A

Insulin recruits GLUT4 glucose transporters from internal vesicles to the plasma membrane, increasing the transport capacity of the membrane

86
Q

Other than glucose, what other macromolecules use the Na+ gradient set up by the Na+, K+, ATPase pump to move from the gut lumen into surrounding cells?

A

Amino acids

87
Q

What prevents glucose moving back down its concentration gradient from cells when there is little glucose in the gut lumen?

A

Glucose is rapidly converted to glucose-6-phosphate upon entering the cell by the actions of glucokinase (cells) and hexokinase (liver) - glucose levels therefore never rise to high enough levels to move down its concentration gradient

88
Q

How does uptake of glucose differ in different cell types? Why?

A

Glucose uptake differs depending on the type of glucose carrier the tissue expresses (GLUT1-7) - these transporters are also not permanently expressed - the level to which they are will depend on the tissue, and it’s priority in needing glucose

Cell Physiology & Pharmacology (5 decks)

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