Effect of local anesthetics on the electrical characteristics of an excitable model membrane composed of dioleyl phosphate

Interactions of some local anesthetics and alcohols with membranes

A review of the results obtained by our group in the last decade regarding the interactions of procaine, lidocaine, dibucaine and tetracaine with membranes is presented in the context of the literature data. The action upon membranes, in first approximation monomolecular film of stearic acid spread at the air/water interface used as a membrane model, the modification of biomembrane structure and function using diffraction methods, lipid phase transition, fluidity of lipids and proteins, membrane expansion and platelet aggregation were studied. The thermodynamic knowledge of membrane-alcohol interactions improved by using highly sensitive calorimetric techniques are briefly reported. One of the main conclusions is that the physical state of a monolayer model membrane was the result of competitive interactions between film-film and film-substrate interactions. It was taken into account that local anesthetics, such as lidocaine, carbisocaine, mesocaine, showed changes in the bilayer structure, reflected in macroscopic mechanical properties. This restructuring of the lipid bilayer has a significant influence on the operation of functional subunits, e.g. ionic channels formed by gramicidin. The results support the concept of non-specific interactions of local anesthetics with lipid bilayers. The theoretical modeling of the interactions of local anesthetics is closely compared with experimental data. Our new theory of relaxation for these interactions is using a non-archimedean formalism based on a process resulting from superpositions of different component processes which take place at different scales of time.

Effect of anesthetics on the self-sustained oscillation in an artificial membrane induced by repetitive conformational change of DOPH molecules between hydrophilic and hydrophobic phases

PURPOSE

The mechanism of anesthesia was approached from a study of an artificial excitable membrane that well reproduced the active electrical properties of the nerve membrane.

METHODS

Self-sustained oscillations of the membrane potential in a model membrane in which dioleyl phosphate (DOPH) was infiltrated into the pores of a millipore filter were utilized to investigate the effect of volatile anesthetic agents on the repetitive conformational change of DOPH molecules between hydrophilic multibilayers and hydrophobic oil droplets, while this process was coupled with diffusion of K⁺ across the membrane placed between KCl aqueous solutions.

RESULTS

The period of the self-sustained oscillations increased due to the addition of volatile anesthetics to the aqueous solutions, and there were critical values of concentrations of volatile anesthetics above which the self-sustained oscillations disappeared.

CONCLUSION

The volatile anesthetic agents affected the hydrophobic oil droplets of the DOPH molecules and impeded their repetitive conformational change between the hydrophilic and hydrophobic phases, just as local anesthetics had been reported to do.

Electrical characteristics in an excitable element of lipid membrane

Electrical characteristics in a membrane constructed from a porous filter adsorbed with a lipid analogue, dioleoyl phosphate (DOPH), were investigated in a situation interposed between 100 mM NaCl + 3 mM CaCl2 and 100 mM KCl. Calcium ions affected significantly the membrane characteristics. The membrane potential was negative on the KCl side, which implies the higher permeability to K+ than Na+; this tendency was increased by a tiny amount of Ca2+. While the membrane showed a low electrical resistance of several k omega . cm2 under K+/Na+ gradient, it showed several M omega . cm2 by Ca2+. The surface structure of the membrane exhibited many voids in the low-resistance state, but the surface was covered by oil droplets in the high-resistance state. Oscillations of the membrane potential appeared spontaneously with application of the electrical current from the KCl side to the NaCl + CaCl2 side. The frequency was increased with the electrical current. All these results were explained comprehensively using an electrochemical kinetic model taking account of the Ca2+ binding effect, where DOPH assemblies make a phase transition between oil droplets due to Ca2+ and multi-bilayers with excess K+. The oscillation arises from coupling of the phase transition to accumulation and release of K+ or Ca2+. This membrane can be used as an excitable element regulated by Ca2+ in neuro-computer devices.

Effect of local anesthetics on the electrical characteristics of an excitable model membrane composed of dioleyl phosphate

The effects of local anesthetics (tetracaine, procaine and lidocaine) on self-sustained electrical oscillations were studied for a lipid membrane comprising dioleyl phosphate (DOPH). This model membrane exhibits oscillation of the membrane potential in a manner similar to that of nerve membranes, i.e., repetitive firing, in the presence of an ion-concentration gradient, on the application of d.c. electric current. Relatively weak anesthetics such as procaine and lidocaine increased the frequency of self-sustained oscillation, and finally induced aperiodic, rapid oscillation. The strong anesthetic tetracaine inhibited oscillation.