IMPEDANCE SPECTROSCOPIC INVESTIGATION OF THE TEMPERATURE INFLUENCE ONTHE TRANSFER OF TETRAPHENYLBORATE IONS THROUGH LIPID-MEMBRANES - CALCULATION OF ENERGY BARRIERS FOR THE ION TRANSFER ACROSS LIPID-MEMBRANES

Investigating the transfer of tetraphenylborate (TPB) ions through pla nar lipid membranes we found a strong influence of temperature on the impedance spectrum. The impedance spectrum of TPB modified lipid membr anes is governed by two processes, namely, the ion transfer at the mem brane surfaces and the ion transfer across the hydrophobic interior of the membrane. The analysis of the measured spectra showed that temper ature predominately influences the inner ion transfer and the rate con stant for the inner transfer, respectively. We used this temperature d ependence to calculate energy barriers for the ion translocation acros s the membrane interior. Varying the composition of the membrane lipid s we found that the inner barrier not only depends on the hydrocarbon part but also on the head group of the lipid. We explain this interest ing result with interactions of the permeating TPB ions with the head groups of the membrane. The above-mentioned interactions seem to immob ilize the TPB ion at the membrane surface and to enlarge the energy ba rrier for the ion transfer across the inner part of the lipid membrane . The largest barriers were found for the investigated lecithins whose phosphocholine head group strongly interacts with the TPB ions. (C) 1 998 Elsevier Science B.V. All rights reserved.