Effects on capacitance by overexpression of membrane proteins.
Functional Channelrhodopsin-2 (ChR2) overexpression of about 10(4)channels/mum(2) in the plasma membrane of HEK293 cells was studied by patch-clamp and freeze-fracture electron microscopy. Simultaneous electrorotation measurements revealed that ChR2 expression was accompanied by a marked increase of the area-specific membrane capacitance (C(m)). The C(m) increase apparently resulted partly from an enlargement of the size and/or number of microvilli. This is suggested by a relatively large C(m) of 1.15+/-0.08 microF/cm(2) in ChR2-expressing cells measured under isotonic conditions. This value was much higher than that of the control HEK293 cells (0.79+/-0.02 microF/cm(2)). However, even after complete loss of microvilli under strong hypoosmolar conditions (100 mOsm), the ChR2-expressing cells still exhibited a significantly larger C(m) (0.85+/-0.07 microF/cm(2)) as compared to non-expressing control cells (0.70+/-0.03 microF/cm(2)). Therefore, a second mechanism of capacitance increase may involve changes in the membrane permittivity and/or thickness due to the embedded ChR2 proteins.
Zimmermann
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D
Department of Biophysical Chemistry, Max-Planck-Institute of Biophysics, Max-von-Laue-Strasse 3, 60438 Frankfurt am Main, Germany.
Zhou
A
A
Kiesel
M
M
Feldbauer
K
K
Terpitz
U
U
Haase
W
W
Schneider-Hohendorf
T
T
Bamberg
E
E
Sukhorukov
V L
VL
D001436:Bacteriorhodopsins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology* / Q000648:ultrastructure; D025802:Electric Capacitance; D005614:Freeze Fracturing; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D018408:Patch-Clamp Techniques
D008565:Membrane Proteins; D001436:Bacteriorhodopsins