Small intestine

Question 1

Examples of co-transporters- what they transport and how much water they also transport

Answer 1

KCC4- potassium/cl co-transporter- also absorbs 500 molecules of water
hSGLT1- sodium/glucose co-transporter- also absorbs 253 molecules of water
GLUT2- facilitated glucose transporter- 40-100 molecules of water
NKCC1- na/k/2cl co-transporter- 590 molecules of water

Question 2

What experiment proved that KCC4 also transports water?

Answer 2

Choroid plexus of a frog- express KCC4
exposed the cells to hypertonic shock- causing the cells to shrink
then added KCL- the cells became swollen
when they added other compounds NaCl for example- cells didnt swell
Did the same experiment with furosemide (blocker of KCC4)- the cells shrink

Question 3

What are the channels found in the apical and basolateral membrane of the small intestine cells?

Answer 3

Apical:
SGLT1- sodium, glucose, water
GLUT2- glucose and water
Basolateral:
ATPase- sodium out, potassium in
KCC- potassium, chloride and water
GLUT2- glucose and water

Question 4

What are the modes of water transport?

Answer 4

AQP1
KCC
Cotransporter- SGLT1, EAAT1

Question 5

So how is water absorbed when the lumen of the intestine is so hypertonic?

Answer 5

Epithelia in the SI remove solute from the lumen
inside the cells becomes slightly hypertonic
small osmotic gradient for water transport
-also: sodium/glucose co transporter- water surrounds the glucose/sodium- becomes trapped in the cleft of the protein transporter- conformational change- water is released into the cell

Question 6

Why was it challenged that membranes are freely permeable to gases?

Answer 6

Membranes used at the time had no cholesterol or membrane proteins in them
also were highly contaminated with decane- which confers a high co2 permeability

Question 7

How does ammonia/ammonium effect the pH of the cell?

Answer 7

Ammonia moves across the bilayer- combines with a proton to form ammonium= alkalisation
slower uptake of ammonium (isnt permeable- moves across via cotransporters such as NKCC)- dissociates to form ammonia and a proton= acidification

Question 8

How does co2/bicarbonate effect the pH of the cell?

Answer 8

co2 moves into the cell- combines with water to form bicarbonate and a proton-= acidification
slower uptake of bicarbonate- combines with a proton to form co2 and water= alkalisation

Question 9

What did they demonstrate using the thick ascending limb in terms of permeability to ammonia/ ammonium?

Answer 9

isolated the TAL- inserted perfusion pipettes
added ammonium chloride to the basolateral side- see predictable alkalisation followed by an acidification
added to the apical side-
only saw a large intracellular acidification
Apical membrane isnt permeable to ammonia

Question 10

Is the gastric gland permeable to co2/ bicarbonate?

Answer 10

Basolateral side is permeable to co2
Apical side isnt permeable to co2
*same with the colonic crypts

Question 11

Why is it beneficial that the stomach isnt permeable to gas?

Answer 11

Means the stomach has tight membranes

has to have tight membranes with restricted transport so it doesn’t digest itself

Question 12

What did experiments with liposomes conclude?

Answer 12

Artificial liposomes- manipulated the cholesterol content:

as cholesterol levels increase- linear relationship with decrease of co2 permeability

Question 13

What did experiments with MDCK cells conclude?

Answer 13

MDCK cells= artificial kidney cell line

if you remove cholesterol with drugs- permeability of co2 shoots up

Question 14

What experiment showed a relationship between co2 permeability and AQP1?

Answer 14

Exposed xenopus oocytes to co2/ bicarb solution- got an expected acidification
the rate of acidification is proportional to the co2 permeability
then exposed these cells to water- the cells swelled up and burst
measured the lysis time and correlated it to co2 permeability
*correlation between acidification and cell lysis time
*turns out that the more AQP1 channels present- the faster the acidification

Question 15

How does pCMBS effect co2 permeability?

Answer 15

Oocytes expressing AQP1= high co2 permeability
add pCMBS= permeability drops
mercury binding to AQP1 is reducing the co2 permeability

Question 16

How did pCMBS affect C189S mutant?

Answer 16

pCMBS did not drop the co2 permeability in the mutant

clearly it is AQP1 conferring the co2 permeability

Question 17

How did we know it wasnt just an artefact (AQP1 and co2 permeability)?

Answer 17

colton null people- no functional AQP1
these people: CO2 permeability of RBCs down by 50%- permeability is unaltered by pCMBS
DIDS= blocks CO2 permeability of AQP1 and rhesus proteins
DIDs+ WT RBCs= co2 permeability down to a third
DIDS + mutant RBCs= CO2 permeability down even more

Question 18

How is CO2 passing through AQP1?

Answer 18

50/50 going through the central and individual pores

Question 19

Which isoforms of AQP4 are permeable to CO2 and which is not?

Answer 19

M23- found in the blood-brain barrier= permeable to co2

M1= not permeable to co2

Question 20

How does cGMP affect AQP1?

Answer 20

Binding of cGMP to AQP1 changes its conformation and switches it from a water pore to a cation channel
cGMP+ AQP1 & 5=
inhibits co2 movement, but then allows cations through
*providing regulation of co2 transport through AQP1