title: A combined patch-clamp and electrorotation study of the voltage- and frequency-dependent membrane capacitance caused by structurally dissimilar lipophilic anions.
abstract: Interactions of structurally dissimilar anionic compounds with the plasma membrane of HEK293 cells were analyzed by patch clamp and electrorotation. The combined approach provides complementary information on the lipophilicity, preferential affinity of the anions to the inner/outer membrane leaflet, adsorption depth and transmembrane mobility. The anionic species studied here included the well-known lipophilic anions dipicrylamine (DPA(-)), tetraphenylborate (TPB(-)) and [W(2)(CO)(10)(S(2)CH)](-), the putative lipophilic anion B(CF(3))(4)(-) and three new heterocyclic W(CO)(5) derivatives. All tested anions partitioned strongly into the cell membrane, as indicated by the capacitance increase in patch-clamped cells. The capacitance increment exhibited a bell-shaped dependence on membrane voltage. The midpoint potentials of the maximum capacitance increment were negative, indicating the exclusion of lipophilic anions from the outer membrane leaflet. The adsorption depth of the large organic anions DPA(-), TPB(-) and B(CF(3))(4)(-) increased and that of W(CO)(5) derivatives decreased with increasing concentration of mobile charges. In agreement with the patch-clamp data, electrorotation of cells treated with DPA(-) and W(CO)(5) derivatives revealed a large dispersion of membrane capacitance in the kilohertz to megahertz range due to the translocation of mobile charges. In contrast, in the presence of TPB(-) and B(CF(3))(4)(-) no mobile charges could be detected by electrorotation, despite their strong membrane adsorption. Our data suggest that the presence of oxygen atoms in the outer molecular shell is an important factor for the fast translocation ability of lipophilic anions.
authors.affiliation: Department of Biophysical Chemistry, Max-Planck Institute of Biophysics, Max-von-Laue Strasse 3, D-60438, Frankfurt am Main, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Zimmermann
authors.forename: M
authors.initials: M
authors.lastname: Kiesel
authors.forename: U
authors.initials: U
authors.lastname: Terpitz
authors.forename: A
authors.initials: A
authors.lastname: Zhou
authors.forename: R
authors.initials: R
authors.lastname: Reuss
authors.forename: J
authors.initials: J
authors.lastname: Kraus
authors.forename: W A
authors.initials: WA
authors.lastname: Schenk
authors.forename: E
authors.initials: E
authors.lastname: Bamberg
authors.forename: V L
authors.initials: VL
authors.lastname: Sukhorukov
mesh_terms: D000818:Animals; D000838:Anions / Q000737:chemistry*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology*; D025802:Electric Capacitance; D005260:Female; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D019169:Jurkat Cells; D009942:Organometallic Compounds / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010851:Picrates / Q000378:metabolism*; D012399:Rotation; D013775:Tetraphenylborate / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D000838:Anions; D009942:Organometallic Compounds; D010851:Picrates; C011454:dipicrylamine; D013775:Tetraphenylborate