Effects on capacitance by overexpression of membrane proteins

Biochem Biophys Res Commun. 2008 May 16;369(4):1022-6. doi: 10.1016/j.bbrc.2008.02.153. Epub 2008 Mar 10.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriorhodopsins / genetics
  • Bacteriorhodopsins / metabolism*
  • Cell Line
  • Cell Membrane / physiology*
  • Cell Membrane / ultrastructure
  • Electric Capacitance*
  • Freeze Fracturing
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Microscopy, Electron
  • Patch-Clamp Techniques


  • Membrane Proteins
  • Bacteriorhodopsins