Giant planar lipid bilayer. III. Maxwell—Wagner impedance dispersion and anesthetic effects upon interfacial capacitance

Interaction of cisplatin with planar model membranes - dose dependent change in electrical characteristics

The drug cisplatin has broad antineoplastic activity against advanced testicular and ovarian cancers, epithelial malignancies, cancers of the head, neck, bladder, oesophagus and lungs. Peripheral neurotoxicity, ototoxicity and nephrotoxicity are its major side effects. The nonspecific action of this drug on the lipid bilayer architecture of membranes has been studied by following the effects produced on the electrical characteristics of model planar bilayer lipid membranes (BLM). The results confirm that the drug has a strong surface interaction with the zwitterionic polar head groups of the amphipathic phospholipids constituting the BLM. The permeability characteristics of cisplatin through the hydrophobic core are limited. Cisplatin does not fluidise the membrane sufficiently to cause its breakdown but creates small ion conducting defects on the membrane bilayer resulting in a marginal increase in ion conductivity. These results indicate that cisplatin exhibits a non-specific action on the lipid bilayer component of the membrane which might be partly responsible for its neurotoxic side effects.

Electrokinetic charge of the anesthetic-induced bR480 and bR380 spectral forms of bacteriorhodopsin

The translational and rotational electrokinetics of the anesthetic-induced spectral transitions bR568-->bR480-->bR380 of bacteriorhodopsin have been investigated. Formation of the bR480 form is associated with an increase of the purple membrane negative electrokinetic charge, while the transformation of bR480 into bR380 is accompanied by a decrease of the membrane negative charge as compared to that of the 480 nm-absorbing form. Removal of anesthetics leads to the back transitions bR480-->bR568 and (in part) bR380-->bR568; however, the electrokinetic charge of the native membranes is not restored. A strong decrease in the electric polarizability and the appearance of a slow polarizability component are also observed in anesthetic-treated membranes. Comparison with the electrokinetic behaviour of partially delipidated membranes and with that of liposomes composed of purple membrane total lipids suggests that: (i) anesthetic molecules partition mainly at the protein/lipid interface inducing irreversible rearrangement of the boundary lipid layer, and (ii) different mode(s) or site(s) of interaction are responsible for the spectral and surface charge effects. The data are compatible with the hypothesis of anesthetics acting through partial dehydration of the membrane surface.

Changes in surface capacitance and conductance parallel to phospholipid membranes associated with phase transition: effects of halothane

The effects of phase transition on the surface capacitance and conductance parallel to dipalmitoyl- (DPPC) and dimyristoyl-phosphatidylcholine (DMPC) membranes were studied by impedance dispersion. The phospholipid aggregates were embedded into pores of a polycarbonate filter and the impedance dispersions were measured at a frequency range from 30 Hz to 1.0 MHz. When the frequency was below 120 kHz, the capacitance showed a peak at the pretransition temperature and a steep rise at the main-transition temperature. In this system, the observed capacitance consists of frequency-dependent and -independent parts. The frequency-dependent part is a surface phenomenon and arises from the lateral motion of counterions at the membrane/water interface. The frequency-independent part represents mainly the properties of the bulk lipid phase. Addition of halothane decreased the total capacitance of the DPPC aggregates at the low frequency range to 1/2 to 1/8 of the control depending upon the temperature. The surface component was solely responsible for this capacitance decrease, because the non-surface component was slightly increased instead. The data suggest that halothane inhibited the lateral ionic flow parallel to the interface.