ATP-Dependant Ion Pumps and Ion Exchangers Flashcards Preview

ESA 2- Membranes and Receptors > ATP-Dependant Ion Pumps and Ion Exchangers > Flashcards

Flashcards in ATP-Dependant Ion Pumps and Ion Exchangers Deck (130):
1

What molecules can pass through membranes?

Hydrophobic or Small, uncharged, polar molecules

2

What molecules cannot pass through membranes?

Large, uncharged polar molecules 
Ions

3

What is passive diffusion dependent on?

Permeability and concentration gradient

4

What happens to the rate of passive transport with an increasing concentration gradient?

It increases linearly

5

What is the permeability of the membrane for a substance increased by?

The incorporation of a specific protein in the bilayer

6

Give two examples of models for facilitated diffusion

Carrier molecules (ping-pong) 
Protein channels

7

What does active transport allow?

The transport of ions or molecules against an unfavourable concentration and/or electrical gradient

8

What does active transport require?

Energy from the hydrolysis of ATP

9

What is wether or not energy is required determined by?

The free energy change of the transported species

10

What is the free energy change of the transported species dependant on?

The free energy change of the transported species, and by the electrical potential across the membrane bilayer when the transported species is charged

11

How much of a cells energy is spent on active transport?

In some cells, up to 30-50%

12

What happens when pores are gated?

They open and close in response to a stimulus

13

Give examples of a stimulus that might open a pore?

Ligand binding to a receptor site 
Change in potential difference across the membrane 
ATP binding

14

Give an example of a voltage-gated ion channel

Na channel

15

Give examples of a ligand-gated ion channels

Nicotinic acetylcholine receptor 
ATP-sensitive K channel

16

Can more than one type of ion/molecule be transported on a membrane transporter per reaction cycle?

Yes

17

What are membrane transporters that transport more than one molecule known as?

Co-transporters

18

Give examples of co-transport

Na-glucose co-transport system of the small intenstine and kidney 
Na/H exchange

19

What happens in Na/H exchange?

Inwards flow of Na down its concentration gradient leads to removal of H, and a rise in cell pH

20

What is a transported in a uniport?

A single molecule in one direction

21

What is transported in a symport?

Two molecules, in the same direction

22

What is transported in an antiport?

Two molecules in opposing directions

23

Where does Na-glucose co-transport occur?

Small intestine and kidney

24

What happens in Na-glucose co-transport?

Entry of Na provides the energy for the entry of glucose against the concentration gradient

25

What kind of transporter is the Na-glucose transporter?

Symport

26

Where is Na/K-ATPase associated?

Plasma membrane

27

What does Na/K-ATPase use to pump ions?

ATP

28

How much of the BMR is used for the Na/K-ATPase?

25%

29

What kind of ATPase is Na/K-ATPase?

P-type

30

What do P-type ATPases do?

ATP phosphorylates aspartate, producing phosphoenzyme intermediates

31

What is the Na/K-ATPase made up of?

α and ß subunits

32

What does the α-subunit do?

Provides the binding site for K, Na, ATP and ouabain

33

What does the ß subunit do?

Glycoprotein directs pump to the surface

34

What does the binding of ouabain to the α-subunit do?

Inhibits Na/K-ATPase

35

What does the Na/K-ATPase do?

Uses energy from ATP hydrolysis to make 2K into the cell and 3 Na out of the cell

36

What kind of transporter is Na/K-ATPase?

Antiport

37

Why is Na/K-ATPase important?

It forms Na and K gradients

38

What are Na and K gradients necessary for?

Electrical excitability

39

What does Na/K-ATPase drive?

Secondary active transport

40

What processes are driven by active transport secondary to the Na/K-ATPase?

Control of pH 
Regulation of cell volume 
Regulation of Ca concentration 
Absorption of Na in epithelia 
Nutrient uptake

41

What is the resting membrane potential?

-70mV

42

What is responsible for the membrane potential?

Mainly, K+ diffusion through channels down its concentration gradient (there are high intracellular K concentrations)

43

What causes high intracellular K concentrations?

Na pump

44

What controls resting Ca concentration?

Ca-ATPases

45

How do Ca-ATPases work?

They use ATP to pump ions

46

What does plasma membrane Ca-ATPase (PMCA) do?

Expels Ca from the cell in exchange for H

47

What does PMCA require?

ATP

48

What kind of transporter is PMCA?

Antiport

49

What is the affinity of PMCA?

High

50

What is the capacity of PMCA?

Low

51

What does PMCA remove?

Residual Ca

52

What does the sarco(endo)plasmic reticulum Ca-ATPase (SERCA) do?

Accumulates Ca into the SR/ER in exchange for H

53

What does SERCA use?

ATP

54

What kind of transporter is SERCA?

Antiport

55

What is the affinity of SERCA?

High

56

What is the capacity of SERCA?

Low

57

What does SERCA remove?

Residual Ca

58

How is the Na/Ca exchanger (NCX) driven?

Secondary active transport, using the Na concentration gradient set up by Na/K-ATPase

59

What does NCX do?

Expels 1 Ca from the cell in exchange for 3 Na

60

What kind of transporter is NCX?

Antiport

61

What is the affinity of NCX?

Low

62

What is the capacity of NCX?

High

63

What does NCX remove?

Most Ca

64

Why is NCX said to be electrogenic?

Because current flows in the direction of the Na gradient

65

When does NCX expel intracellular Ca?

During cell recovery

66

What is the activity of NCX dependant on?

Membrane potential

67

What happens to NCX when the membrane is depolarised?

It reverses the mode of operation

68

Give an example of where the reversal of the NCX mode of operation is important?

Ca influx during the cardiac action potential

69

How can NCX contribute to ischaemic injury?

ATP is depleted in ischaemia, and the Na pump is therefore inhibited, so Na accumulates in the cell, leading to depolarisation, and so NCX reverse. Na moves out, Ca moves in. High Ca is toxic

70

What are the two acid extruders?

Na/H exchanger (NHE)
Sodium bicarbonate co-transporter (NBC)

71

What does NHE do?

Exchanges extracellular Na for intracellular H

72

Is NHE electrogenic?

No- it is electroneutral

73

Why is NHE electroneutral?

Because there is 1:1 charge exchange

74

What does NHE use to drive it?

The Na concentration gradient set up by Na/K-ATPase

75

What does NHE act to do?

Raise intracellular pH and regulate cell volume

76

What activates NHE?

Growth factors

77

What inhibits NHE?

Amiloride

78

What is NBC also known as?

Na dependent Cl/HCO3 exchanger

79

Essentially, what happens with NBC?

Acid out 
Base in

80

What does NBC use?

The Na concentration gradient set up by Na/K-ATPase

81

What does NBC act to do?

Raise intracellular pH
Regulate cell volume

82

What is the base extruder?

Anion exchanger (AE)

83

What does the AE do?

Exchanges Cl for HCO3-

84

What does the AE serve to do?

Acidify cell 
Involved in cell volume regulation

85

What happens to pH in the cell?

It is held at the set point. Any drift away from this pH is corrected by the increased activity of exchangers

86

What happens as the cell becomes more acidic?

There is more substrate for NHE, and so more acid is removed from the cell, so the pH is restored towards alkaline

87

What happens as NHS extrudes too many H ions?

The pH goes where it needs to be, and so the activity of the anion exchanger cuts in

88

How does ion transport regulate cell volume?

Osmotically active ions or organic osmolytes are transported either into or out of cells, and water follows, causing cell swelling and shrinking

89

Give 3 examples of osmotically active ions

Na
K
Cl

90

What are organic osmolytes?

Amino acids

91

What is the standard method for cell volume regulation?

There is no standard method- different cell types use particular combinations of transporters to achieve the regulation they need

92

What happens if the cell is swelling?

Ions are extruded, e.g. through K and Cl channels, and so water is lost

93

What happens if the cell is shrinking?

There is an influx of ions, e.g. through Na and Ca channels, and so water is gained

94

How is bicarbonate reabsorbed by the proximal kidney tubule?

Na/K pump drives other channels, in this case keeping intracellular Na concentration low, so NHE can pump H ions into the proximal tubule lumen. H then goes into the lumen to ‘pick up’ bicarbonate and bring it back into the cell

95

How much bicarbonate does the kidney reabsorb under normal circumstances?

All of it

96

What is the main reason to retain base?

For pH buffers

97

What is the goal of renal anti-hypertensive therapy?

To reduce the reuptake of Na and other molecules, so less water is absorbed by osmosis, and so blood volume and therefore blood pressure falls

98

What are aquaporin allow?

Water to more readily cross the membrane

99

What is aquaporins inclusion in the membrane stimulated by?

Anti-diuretic hormone (ADH)

100

What mechanisms to allow Na reuptake from the filtrate to the blood are there in the thick ascending limb?

NKCC2 
Na-K-ATPase

101

What does NKCC2 do?

Moves Na, K and 2Cl into the endothelium of the nephron

102

How does NKCC2 move Na into the blood?

Using the Na gradient to drive Na

103

How is Na passed from endothelium into the blood?

Na-K-ATPase

104

What is required due to the action of NKCC2?

The kidney needs to deal with the K and Cl bought in if it wants to maintain the same potential

105

What mechanisms does the thick ascending limb have to deal with K and Cl?

KClCT 
ROMK

106

What does KClCT do?

K-Cl cotransport that salvages both ions back into the blood

107

What does ROMK do?

Allows efflux of K back into filtrate

108

What blocks the action of NKCC2?

Loop diuretics

109

What is the effect of loop diuretics?

They bind to NKCC2 transporters, inhibiting them and therefore more Na is lost in the filtrate. Water follows, thus reducing blood volume, thus blood pressure

110

What is the purpose of the distal convoluted tubule?

To allow ions to equilibrate

111

What mechanisms are present in the distal convoluted tubule?

NCCT
ENaC
TRPM6
CIC-K6
KCICT
NCX
Na pump

112

What does NCCT do?

Cotransport of Na and Cl

113

What inhibits NCCT?

Thiazides

114

What does ENaC do?

Allow Na into the endothelium of nephron

115

Is ENaC voltage sensitive?

No

116

What inhibits ENaC?

Amiloride

117

What does TRPM6 do?

Allows Ca and Mg into the endothelium of the nephron, and thus allowing retention of Ca

118

What does CIC-K6 do?

Brings Cl into the blood from the endothelium

119

What does NCX do?

Brings 3 Na into endothelium for 1 Ca into blood

120

What mechanisms does the cortical collecting tube have?

Aquaporin
ROMK
ENaC
CLC
Na pump

121

What does aquaporin do?

Allows water into blood

122

Why is it important that water is taken up in the kidney?

So it allows water to follow Na, maintaining blood pressure

123

What stimulates aquaporin?

Anti-diuertic hormone

124

What does ROMK do?

Allows K efflux into blood

125

What does ClC do?

Allows Cl into the blood

126

What does aldosterone do?

Upregulates ENaC, ROMK and the Na pump, leading to increase Na retention, and therefore increased water retention

127

What is found in some cases of hypertension?

That there is an increased production of aldosterone and therefore over retention of Na through the epithelial sodium channel

128

How can aldosterone stimulated hypertension be treated?

Using spironolactone

129

What is spironolactone?

A mineralocorticoid receptor antagonist

130

What does spironolactone do?

Binds to aldosterone receptors, stopping the overexpression of these proteins