title: Cellular pH measurements in Emiliania huxleyi reveal pronounced membrane proton permeability.
abstract: • 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.
authors.affiliation: Physiologisches Institut, CAU Kiel, Kiel, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Suffrian
authors.forename: K G
authors.initials: KG
authors.lastname: Schulz
authors.forename: M A
authors.initials: MA
authors.lastname: Gutowska
authors.forename: U
authors.initials: U
authors.lastname: Riebesell
authors.forename: M
authors.initials: M
authors.lastname: Bleich
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism; D002138:Calibration; D002245:Carbon Dioxide / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D003584:Cytological Techniques / Q000379:methods*; D005452:Fluoresceins / Q000494:pharmacology; D058087:Haptophyta / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D009550:Nigericin / Q000378:metabolism; D011522:Protons; D012623:Seawater / Q000737:chemistry; D012996:Solutions
chemical_list: D001639:Bicarbonates; D005452:Fluoresceins; D011522:Protons; D012996:Solutions; D002245:Carbon Dioxide; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D009550:Nigericin