Cellular pH measurements in Emiliania huxleyi reveal pronounced membrane proton permeability

New Phytol. 2011 May;190(3):595-608. doi: 10.1111/j.1469-8137.2010.03633.x. Epub 2011 Feb 7.


• To understand the influence of changing surface ocean pH and carbonate chemistry on the coccolithophore Emiliania huxleyi, it is necessary to characterize mechanisms involved in pH homeostasis and ion transport. • Here, we measured effects of changes in seawater carbonate chemistry on the fluorescence emission ratio of BCECF (2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein) as a measure of intracellular pH (pH(i)). Out of equilibrium solutions were used to differentiate between membrane permeation pathways for H(+), CO(2) and HCO(3)(-). • Changes in fluorescence ratio were calibrated in single cells, resulting in a ratio change of 0.78 per pH(i) unit. pH(i) acutely followed the pH of seawater (pH(e)) in a linear fashion between pH(e) values of 6.5 and 9 with a slope of 0.44 per pH(e) unit. pH(i) was nearly insensitive to changes in seawater CO(2) at constant pH(e) and HCO(3)(-). An increase in extracellular HCO(3)(-) resulted in a slight intracellular acidification. In the presence of DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid), a broad-spectrum inhibitor of anion exchangers, E. huxleyi acidified irreversibly. DIDS slightly reduced the effect of pH(e) on pH(i). • The data for the first time show the occurrence of a proton permeation pathway in E. huxleyi plasma membrane. pH(i) homeostasis involves a DIDS-sensitive mechanism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / pharmacology
  • Bicarbonates / metabolism
  • Calibration
  • Carbon Dioxide / metabolism
  • Cell Membrane Permeability* / drug effects
  • Cytological Techniques / methods*
  • Fluoresceins / pharmacology
  • Haptophyta / cytology*
  • Haptophyta / drug effects
  • Haptophyta / metabolism*
  • Hydrogen-Ion Concentration / drug effects
  • Intracellular Space / drug effects
  • Intracellular Space / metabolism
  • Kinetics
  • Nigericin / metabolism
  • Protons*
  • Seawater / chemistry
  • Solutions


  • Bicarbonates
  • Fluoresceins
  • Protons
  • Solutions
  • Carbon Dioxide
  • 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein
  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid
  • Nigericin