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Membranes and Receptors > Lecture 2 - Membrane Permeability, Cell Volume and pH Regulation; ATP Dependent Ion Pumps and Ion Exchangers > Flashcards

Lecture 2 - Membrane Permeability, Cell Volume and pH Regulation; ATP Dependent Ion Pumps and Ion Exchangers Flashcards

1
Q

What molecules can pass through membranes?

A

Hydrophobic molecules

Small, uncharged, polar molecules

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2
Q

What molecules can’t pass through membranes?

A

Large, uncharged, polar molecules

Ions

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3
Q

What is passive diffusion?

A

Dependent on permeability and concentration gradient

Rate increases linearly with increasing concentration gradient

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4
Q

What is facilitated diffusion?

A

Permeability for substance is increased by incorporation of a specific protein in the bilayer.

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5
Q

What is active transport?

A

Transport of ions or molecules against the favourable concentration gradient
Energy may be required depending on concentration gradient and electrochemical gradient

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6
Q

What is a cotransporter?

A

Membrane transporter that transports more than one molecule.

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7
Q

What is uniport?

A

One molecule is transported in one direction.

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8
Q

What is symport?

A

Two molecules are transported in the same direction.

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9
Q

What is antiport?

A

Two molecules are transported in opposing directions.

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10
Q

What is Na K ATPase?

A

Plasma membrane associated pump
Uses ATP to pump ions
P type ATPase

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11
Q

What is the structure of Na K ATPase?

A

alpha subunit - binding site for K, Na, ATP and ouabain

beta subunit - glycoprotein directs pump to surface

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12
Q

What does ouabain do?

A

Binds to alpha subunit - inhibits Na K ATPase.

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13
Q

What does Na K ATPase do?

A

Uses energy from ATP hydrolysis
moves 2K into the cell
moves 3Na out of the cell
forms Na and K gradients

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14
Q

what does Na K ATPase driving secondary active transport do?

A 
control of pH
regulation of cell volume
regulation of Ca concentration
absorption of Na in epithelia
nutrient uptake
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15
Q

what is the function of K channels?

A

allows K diffusion down the concentration gradient set up by Na K ATPase
mainly responsible for membrane potential

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16
Q

what is the resting membrane potential?

A

-70mV

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17
Q

what is the role of Ca ATPases?

A

control of resting Ca concentration

uses ATP to pump ions by active transport

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18
Q

what is the role of pmca?

A

Expels Ca from the cell, high affinity, low capacity

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19
Q

what is the role of serca?

A

Accumulates Ca in the SR/ER, high affinity, low capacity

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20
Q

what is the role of ncx?

A

Inward flow of Na down its concentration gradient drives outward flow of Ca up its concentration gradient, low affinity, high capacity

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21
Q

what happens to ncx in ischaemia?

A 
atp is depleted in ischaemia
Na K ATPase is inhibited
Na accumulates in cell leading to depolarisation
ncx reverses
Na moves out, Ca moves in 
high Ca is toxic
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22
Q

what is the role of nhe?

A

Inward flow of Na down its concentration gradient leads to cell alkalisation by removing H

23
Q

what is the role of nbc (sodium bicarbonate cotransporter) and Na dependent Cl HCO3 exchanger?

A 
acid out
base in
uses Na gradient set up by Na K ATPase
raises intracellular pH
regulates cell volume
24
Q

what is the role of ae (anion exchanger) and Cl HCO3 exchanger?

A

base out
acid in
cell volume regulation

25
Q

how is cell swelling reversed?

A

extrude ions

26
Q

how is cell shrinking reversed?

A

influx ions

27
Q

what are osmotically active ions?

A

Na
K
Cl
organic osmolytes (amino acids)

28
Q

how is bicarbonate reabsorbed in the proximal tubule?

A

Na K ATPase keeps intracellular Na low so nhe can pump H into the proximal tubule lumen
H picks up bicarbonate in the lumen and brings it back into the cell

29
Q

what do loop diuretics do?

A

block Na reuptake in the thick ascending upper limb

30
Q

what does amiloride do?

A

acts in distal convoluted tubule (ENaC) and proximal convoluted tubule (Na/H) to prevent Na reuptake

31
Q

what does aldosterone do?

A

upregulates these transporters

32
Q

what does sprionolactone do?

A

glucocorticoid receptor antagonist - used to treat if aldosterone is high

33
Q

why does cystic fibrosis cause thick mucous?

A

normally transport of Na out of the cell by Na K ATPase allows for symport of Cl into cell with Na and K
faulty ctfr protein leads to accumulation of Cl in cell
water moves into the cell via osmosis leaving thick viscous mucous in the lumen

34
Q

what happens in diarrhoea?

A

ctfr is overly active once phosphorylated by pka
Cl is excessively transported into lumen
water follows leading to symptoms of diarrhoea

35
Q

How does water move across membranes?

A

Osmosis

36
Q

What increases a membrane’s permeability?

A

Specific channels

37
Q

What is the difference in Cl permeability in a phosphatidylserine bilayer compared with an erythrocyte membrane?

A

10^7 fold.

38
Q

What protein is responsible for Cl transport?

A

Band 3

39
Q

What does the Band 3 protein do?

A

Carries out the specific exchange of Cl for HCO3.

40
Q

What does a ligand gated ion channel do?

A

Open or close in response to ligand binding to a receptor site.

41
Q

What does a voltage gated channel do?

A

Open or close in repsonse to potential difference across the membrane.

42
Q

What does a gap junction do?

A

Close when cellular calcium concentration rises above 10 micromoles or the cell becomes acid.

43
Q

What determines whether a molecule moves by passive or active transport?

A

The free energy change of the transported species.

44
Q

How is the free energy change of the species determined?

A

The concentration gradient for the transported species and the electric potential across the membrane when the species is charged.

45
Q

Where does the free energy driving active transport come from?

A

Directly or indirectly from the hydrolysis of ATP

46
Q

What drives ATP synthesis in mitochondria?

A

A gradient of H+ ions via an ATP dependent proton transporter.

47
Q

What is secondary active transport?

A

The transport of one substance is linked to the concentration gradient for another via a cotransporter, so hydrolysis of ATP is used indirectly

48
Q

What is the role of the Na glucose co transport system of the small intestine and kidney?

A

Entry of sodium provides the energy for entry of glucose

49
Q

What is the role of mitochondrial Ca uniports?

A

Operate at high Ca concentration to buffer potentially damaging concentrations

50
Q

When cellular buffering capacity is exceeded, how is cellular pH controlled?

A

Plasma membrane transporters

51
Q

How is acidification opposed?

A

Expelling H+ or inward movement of bicarbonate ions

52
Q

How is alkalinisation opposed?

A

Expelling bicarbonate via the anion exchanger

53
Q

What does electroneutral transport of ions allow?

A

The osmotic strength of the cytoplasm to be varied without affecting the membrane potential

Membranes and Receptors (10 decks)

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