The Journal of Membrane Biology

, Volume 70, Issue 2, pp 147–155 | Cite as

Carrier-mediated ion transport through black membranes of lipid mixtures and its coupling to Ca++-induced phase separation

  • G. Schmidt
  • H. Eibl
  • W. Knoll
Articles

Summary

Voltage jump-current relaxation experiments have been performed with valinomycin-doped membranes of mixtures of 1,2-dipentadecylmethylidene-glycero-3-phosphorylcholine (PC) and charged-phosphatidic acid (PA). Both relaxation processes predicted by a simple carrier model could be resolved which allowed the calculation of the rate constants of the Rb+ transport. The dependence of the rate constants on the membrane composition indicates that (i) the lipids in the mixed membranes are homogeneously distributed and that (ii) no major difference exists between the composition of the membrane and that of the torus. The analysis of the stationary conductance data, however, shows that the valinomycin content of the mixed membranes depends strongly on their lipid composition. Addition of Ca++ ions to a 1∶1 mixture induces a phase separation into PA domains of very low conductivity and PC-enriched regions of high conductivity. Half saturation is reached atcca=5×10−4m. At 10−2m Ca++ in the aqueous phase, the rate constants clearly indicate that all PA molecules are electrically “passivated” and only pure PC domains contribute to the membrane current. A detailed picture is thus derived of the coupling of a model transport system to the externally triggered membrane reorganization.

Key Words

black lipid membranes carrier-mediated ion transport lipid mixture Ca++-induced phase separation 

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Copyright information

© Springer-Verlag New York Inc. 1982

Authors and Affiliations

  • G. Schmidt
    • 1
  • H. Eibl
    • 2
  • W. Knoll
    • 1
  1. 1.Physik Department E 22Technische Universität MünchenGarchingWest Germany
  2. 2.Max-Planck-Institut für Biophysikalische ChemieGöttingenWest Germany

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