Volker endeward fabian itel samer al samir mohamed chami fredrik berg kristina hedfalk gerolf gros
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Intrinsic CO 2 permeability of cell membranes and role of CO 2 channels. Volker Endeward, Fabian Itel, Samer Al-Samir, Mohamed Chami, Fredrik Öberg, Kristina Hedfalk, Gerolf Gros. Intrinsic CO 2 permeability of a red cell membrane. Gas permeability of synthetic phospholipid bilayers.

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Volker endeward fabian itel samer al samir mohamed chami fredrik berg kristina hedfalk gerolf gros

Intrinsic CO2 permeability of cell membranes and role of CO2 channels

Volker Endeward, Fabian Itel, Samer Al-Samir, Mohamed Chami, Fredrik Öberg,Kristina Hedfalk,Gerolf Gros


Intrinsic co 2 permeability of a red cell membrane
Intrinsic CO2 permeability of a red cell membrane


Gas permeability of synthetic phospholipid bilayers
Gas permeability of synthetic phospholipid bilayers

Alberts et al.

Molecular Biology Of The Cell, 4th Edition


CO2

?

1. What are the intrinsic CO2 permeabilities of cell membranes?

  • Which mechanisms are responsible for the given intrinsic

  • permeabilities of cell membranes?


1. What are the intrinsic CO2 permeabilities of cell membranes?


Mass spectrometer

H

16

O + C

18

O

16

O

2/

3

2

HC

18

O

16

O

-

+ H

+

2

1/

3

H

18

O

+ C

16

O

2

2

P

HCO3

-

P

H2O

P

CO2

H

18

O

+ C

16

O

1/3

2

2

H C

18

O

16

O

-

+ H

+

CA

2

2/3

H

16

O + C

18

O

16

O

2

Cell


Cell membranes show co 2 permeabilities lower then synthetic lipid bilayer
Cell membranes show CO2 permeabilities lower then synthetic lipid bilayer



PC:PS:Chol – vesicles with different cholesterol content

PC = Phosphatidylcholine

PS = Phosphatidylserine

Chol = Cholesterol (0 – 70%)

Ø = ~ 150 nm


70% chol.

[C18O16O] - [C18O16O]∞ (µM)

30% chol.


Effect of cholesterol on lipid vesicle co 2 permeability
Effect of cholesterol on lipid vesicle CO2 permeability

>0.16 cm/s

PC:PS = 8:2



CO vesicles2 permeabilities of cell membranes appear to be essentially determined by their cholesterol content


cholesterol depletion vesicles

with β-cyclodextrin

cholesterol enrichment

with β-cyclodextrin


Is cholesterol the cause of the low co 2 permeability of mdck cells
Is cholesterol the cause of the low CO vesicles2 permeability ofMDCK cells?

Reduction of cholesterol with cyclodextrin raises PCO2.

Enrichment with cholesterol lowers PCO2 compared to normal cells.


  • We show that cell membranes possess a low intrinsic CO vesicles2 permeability, often in the range of 0.01 cm/s.

  • This permeability is 2, and in one case 3, orders of magnitude lower than the CO2 permeability of pure artificial phospholipid bilayers.

  • The main cause of this low CO2 permeability is the cholesterol content of the cell membrane. With increasing cholesterol content PCO2 decreases

  • in artificial vesicles as well as in intact cells.


Physiological consequences of low vesiclesCO2 membrane permeabilities

1. Consequences of the extremely low CO2 permeability of the

apical membrane of colon epithelium

2. Effect of low CO2 membrane permeability on red blood cell

gas exchange


P vesiclesCO2 = 0.0015 cm/s

Consequences of low apical CO2 permeability in colonocytes

apical membrane

basal membrane

100

colon lumen

pCO

2

(

mmHg

)

capillary

40

20

0

diffusion pathway (µm)




AQP1 cells with

AqpZ


Aquaporin 1 as a co 2 channel in cholesterol containing lipid vesicles
Aquaporin 1 as a CO cells with 2 channel in cholesterol-containing lipid vesicles

PC:PS:Chol 8:2:10

Incorporation of AQP1 into vesicles causes a rise in PCO2

Change of PCO2 in vesicles with decreasing Lipid- Protein-Ratios (LPR)


Dids reduces the co 2 permeability of aqp1 containing vesicles
DIDS reduces the CO cells with 2 permeability of AQP1 containing vesicles


Aquaporin 1 as a co 2 channel in mdck cells
Aquaporin 1 as a CO cells with 2 channel in MDCK cells

Expression of AQP1 in MDCK cells raises PCO2



Summary
Summary content and low

With rising cholesterol content the CO2 permeability ( PCO2) of lipid vesicles decreases drastically.

The intrinsic PCO2 of cell membranes is low due to their cholesterol content:

1) cell membranes and lipid vesicles with identical cholesterol content exhibit identical CO2 permeability

2) cholesterol-depleted cell membranes have an increased CO2 permeability, cholesterol-enriched cell membranes a reduced permeability

Cell membranes with normal cholesterol raise their CO2 permeability, when functionally required, by incorporation of CO2 channels:

1) AQP1 incorporated in lipid vesicles raises CO2 permeability in a concentration-dependent manner

2) AQP1 expression in MDCK cells increases membrane PCO2.


Medizinische Hochschule Hannover content and low

Vegetative Physiologie

Samer Al-Samir

Timo Meine

Werner Zingel

Gerolf Gros

Universität BaselDept. Chemie / Biozentrum

Fabian Itel

Mohamed Chami

University of GothenburgDept. Chemistry/Biochemistry

Frederic Öberg

Kristina Hedfalk


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