Lecture 13 - AQP continued 2

Question 1

Small intestine membrane proteins

Answer 1

AQP on both apical and basolateral membranes

sodium, chloride and other solutes transported from the lumen to the blood

Question 2

Small intestine osmolality

Answer 2

high in the lumen but isotonic in the blood, there are high levels of H2O absorption

Question 3

Wet transport proteins

Answer 3

co-transporters that also transport water as part of their normal operation

Question 4

Co-transport is…

Answer 4

against the osmotic gradient

Question 5

Co-transport and osmosis used when..

Answer 5

the transport of solute changes the osmolality which int urn drives osmosis

Question 6

Overton’s Law

Answer 6

the permeability of a membrane to a solute is proportional to the oil/water partition coefficient for that solute

Question 7

natural extension fo Overton’s Law

Answer 7

because gases such as O2 or CO2 have a high solubility in oil, so all biological membranes were freely permeable to gases

Question 8

Bilayer experiment with no cholesterol or proteins

Answer 8

show very high CO2 permeability

But it uses decaf which increases gas permeability, therefore may not be fully valid

Question 9

NH4/NH3 ratio

Answer 9

19NH4 to 1NH3 in solution

Question 10

NH4/NH3 experiment for pHi

Answer 10

expose cell to solution
both cross the membrane but NH3 has a higher permeability so enters cell and binds H+ which causes the cell to undergo alkalisation
Slower NH4 enters cell through proteins, dissociates and releases H so acidification occurs

Question 11

CO2/HCO3 experiment on pHi

Answer 11

Co2 enters cell and combines with H2O but then dissociates to HCO3 and H+ causing acidification
HCO3 is charged so uses transporters to enter, binds H+ so alkalisation

Question 12

thick ascending limb basolateral membrane permeability

Answer 12

high permeability to both NH4 and NH3

Question 13

Thick ascending limb apical membrane permeability

Answer 13

high NH4 permeability but low NH3 permeability

as it is impermeable to H2O it is likely to be impermeable to NH3

Question 14

Gastric gland basolateral membrane

Answer 14

with CO2 it shows small acidification therefore shows permeability to CO2

Question 15

Gastric gland apical membrane

Answer 15

with high conc CO2 there is no effect, therefore CO2 impermeable

Question 16

Low gas permeability is linked to

Answer 16

membrane cholesterol content as it reduces fluidity

Question 17

Artificial liposome experiment

Answer 17

to increase cholesterol therefore decrease CO2 permeability

Question 18

Gastric gland apical membrane cholesterol

Answer 18

75%

Question 19

membranes with low cholesterol levels

Answer 19

CO2 permeability is high enough to support metabolic demands

Question 20

Membranes with high cholesterol levels

Answer 20

provides barrier function so limits gas function

Question 21

Co2 on pHi in xenopus oocytes

Answer 21

no background permeability for HCO3-
So CO2 rate not effected by HCO3- transport
acidification rate is proportional to CO2 permeability

Question 22

AQP1 H2O and CO2 permeability

Answer 22

measuring cell burst to find increased water permeability

Question 23

CO2 and H2O correlation

Answer 23

CO2 permeability is proportional to H2O permeability

Question 24

More AQP1 channels means

Answer 24

faster rate of acidification

Question 25

CO2 permeability is proportional to…

Answer 25

AQP1 expression

Question 26

pCMBs

Answer 26

organic mercurial compound that binds to exposed cysteine residues

Question 27

pCMBs and acidification

Answer 27

acidification rate decreases with pCMBs to baseline levels

Question 28

Proof AQP1 is a CO2 channel

Answer 28

express C189S mutant so pCMBs can no longer bind

this shows high permeability proving AQP1 increases CO2 permeability

Question 29

Colton Null

Answer 29

linked to lack of AQP1 expression or mutant AQP1 in RBCs

Question 30

Colton null CO2 permeability

Answer 30

reduced

unaffected by pCMBs

Question 31

DIDs and RBCs

Answer 31

inhibits CO2 permeability

proves there is an additional way CO2 enters the cell

Question 32

CO2 movement in RBC (3 ways)

Answer 32

50% AQP1, 45% Rhesus-associated glycoproteins and 5% across lipid bilayer

Question 33

Rhesus-associated proteins

Answer 33

permeable to NH3 and CO2

Question 34

DIDS effect of AQP1

Answer 34

inhibits CO2 movement but H2O can still move through

Question 35

CO2 movement through AQP1

Answer 35

moves through the 4 water pores and the central pore equally

Question 36

O2 movement through AQP1

Answer 36

through central pore mainly

Question 37

cGMP effect on AQO1

Answer 37

AQP1 is sensitive to cGMP binding and activates ion conductance
proves central pore can be used as a cation channel
knocks out CO2 permeability