Volumetric study on the protein-anesthetic binding.

Thermodynamic equations describing the volume behavior of protein-ligand mixtures in water were derived. In order to estimate the volume and binding parameters, the equations were combined with a Langmuir-type binding isotherm. Densities of aqueous solutions of mixtures of bovine serum albumin (BSA) and octanol (C8OH) were measured as a function of total BSA molality, m(M)(T), at constant total C8OH molalities, m(X)(T). The data were analyzed by the equations. The partial molar volumes at infinite dilution of BSA and C8OH, V(M)(T,0) and V(X)(T,0), respectively, were estimated. It was seen that V(M)(T,0) decreases by the addition of C8OH to the solution and that V(X)(T,0) decreases gradually with increasing m(M)(T) and approaches asymptotically to a certain value at high m(M)(T). From the concentration dependence of V(M)(T,0) and V(X)(T,0), the values of the association constant K=392 kg mol(-1), the maximum binding number b(max)=1.9, and the volume change DeltaV=-109 cm(3) mol(-1) were obtained for BSA-C8OH interaction in water. The negative value of DeltaV indicates that the hydrophobic interaction reduces the protein volume and elevation of pressure promotes BSA-C8OH binding. These results is inconsistent with the pressure reversal of anesthesia.

Solubilization study of local anesthetics into sodium dodecyl sulfate micelle using anesthetic cation selective electrodes.

The free concentrations of local anesthetic cations in equilibrium with sodium dodecyl sulfate (SDS) micelle which solubilized the anesthetic were determined by using ion-selective electrodes sensitive to local anesthetics, procaine (PC), lidocaine (LC), and mepivacaine (MC). Solubilizate distribution between water and SDS micelle was analyzed by means of the stepwise mass-action model. Association constant, K(1), was found to depend upon the anesthetic concentration, which decreased exponentially as the concentration of free anesthetic increased. Therefore, K(1) should include the interaction function φ(A) as K(1)=K(int)exp{-φ(A)} where K(int) is an intrinsic association constant. φ(A) is an increasing function of the anesthetic concentration, which means that occupation of a solubilization site by a local anesthetic cation makes sequential solubilization more difficult. The binding affinity of an anesthetic with SDS micelle increased in the following order PC

Partitioning of uncharged local anesthetic benzocaine into model biomembranes.

The partitioning of uncharged local anesthetic benzocaine (BzC) into molecular aggregates formed by cationic surfactant decylammonium chloride (DeAC) and phospholipid dipalmitoylphosphatidylcholine (DPPC) was studied from the surface tension and light transmittance measurements. The quantities concerning the partitioning of BzC, the compositions of BzC in the surface-adsorbed film and micelle and three kinds of differential partition coefficients corresponding to phase transitions of the DPPC bilayer membrane were evaluated from thermodynamic analysis of the experimental data. The surface-adsorbed film and micelle were more abundant in BzC than the aqueous solution and significantly large differential partition coefficients for the DPPC membranes were observed. The results clearly showed that the BzC molecules greatly partitioned into hydrophobic environments produced by surfactant-monolayer and phospholipid-bilayer membranes. The partitioning behavior of BzC was also compared with that of charged local anesthetic procaine hydrochloride (PC.HCl). It was shown that the PC.HCl molecule did not or hardly partition into such hydrophobic environments. The contrasting results of the partitioning between BzC and PC.HCl are attributable to the drastic decrease of hydrophilicity of BzC due to the lacking of ionic polar head group in comparison with PC.HCl.

Partition coefficients of charged and uncharged local anesthetics into dipalmitoylphosphatidylcholine bilayer membrane: estimation from pH dependence on the depression of phase transition temperatures.

Effects of the local anesthetics, dibucaine, bupivacaine and lidocaine on the phase transition temperatures of dipalmitoylphosphatidylcholine (DPPC) bilayer membrane were studied by the optical method. We focus our attention on pH dependence of the depression of main transition and pretransition temperatures. The temperatures of both transitions of DPPC bilayer membrane were depressed by the addition of anesthetics; the higher the value of pH, the larger the depression of main transition temperature and/or pretransition temperature by anesthetics. By extending the colligative thermodynamic framework to the depression of main transition temperature by an anesthetic, we can estimate the differential partition coefficient, which is defined by the difference in partition coefficients of an anesthetic into the ripple gel and liquid crystal phases. The difference in partition coefficient between the lamellar and ripple gel phases can also be estimated from the depression of pretransition temperature. Since the differential partition coefficients include both contributions of the charged and uncharged anesthetics, we could estimate the partition coefficients of the charged and uncharged anesthetic into the membranes from the pH dependence of differential partition coefficients. The liquid crystalline membrane of DPPC bilayer was more receptive to the uncharged local anesthetics than the charged species. The partition coefficients of the charged and uncharged anesthetics into the liquid crystalline phase of DPPC bilayer membrane were 3540 and 249000 (for dibucaine), 1120 and 83900 (for bupivacaine), 256 and 11700 (for lidocaine), respectively. The transfer free energy of uncharged anesthetics from the aqueous phase to the liquid crystalline membrane was well correlated to the local anesthetic potency.

Effect of local anesthetics on the bilayer membrane of dipalmitoylphosphatidylcholine: interdigitation of lipid bilayer and vesicle-micelle transition.

The phase transitions of dipalmitoylphosphatidylcholine (DPPC) bilayer membrane were observed by means of differential scanning calorimetry (DSC) as a function of the concentration of local anesthetics, dibucaine (DC x HCl), tetracaine (TC x HCl), lidocaine (LC x HCl) and procaine hydrochlorides (PC x HCl). LC x HCl and PC x HCl depressed monotonously the temperatures of the main- and pre-transition of DPPC bilayer membrane. The enthalpy changes of both transitions decreased slightly with an increase in anesthetic concentration up to 160 mmol kg(-1). In contrast, the addition of TC x HCl or DC x HCl, having the ability to form a micelle by itself, induced the complex phase behavior of DPPC bilayer membrane including the vesicle-to-micelle transition. The depression of both temperatures of the main- and pre-transition, which is accompanied with a decrease in enthalpy, was observed by the addition of TC x HCl up to 21 mmol kg(-1) or DC x HCl up to 11 mmol kg(-1). The pretransition disappeared when these concentrations of anesthetic were added, and the interdigitated gel phase appeared above these concentrations. The appearance of the interdigitated gel phase, instead of the ripple gel phase, brings about the stabilization of the gel phase by 1.8-2.4 kcal mol(-1). In the concentration range of 70-120 mmol kg(-1) TC x HCl (or 40-60 mmol kg(-1) DC x HCl), the enthalpy of the main transition exhibited a drastic decrease, resulting in the virtual disappearance of the main transition. This process includes the decrease in vesicle size with increasing anesthetic concentration, resulting in the mixed micelle of DPPC and anesthetics. Therefore, in this range of anesthetic concentration, the DPPC vesicle solubilized an anesthetic which coexists with the DPPC-anesthetic mixed micelle. Above the concentration of 120 mmol kg(-1) TC x HCl (or 60 mmol kg(-1) DC x HCl), there exists the DPPC-anesthetic mixed micelle. Two types of new transitions concerned with the mixed micelle of DPPC and micelle-forming anesthetics were observed by DSC.

Intra-axonal continuous measurement of lidocaine concentration and pH in squid giant axon.

PURPOSE: To measure the dynamic penetration process of lidocaine, lidocaine concentration (Ci) and pH (pHi) in squid giant axon, and to determine the times and Ci of disappearance and reappearance of action potentials (AP). METHODS: Lidocaine solutions adjusted to four different pHs (pH = 5.5, 6.8, 7.8 and 9.0) were externally administered to the axon and Ci and pHi were measured using lidocaine and pH microsensors. The times and Ci when the AP just disappeared and reappeared were recorded. In addition, for comparison with Ci, the lidocaine content in the whole axon (Cw) was measured with high-performance liquid chromatography (HPLC). RESULTS: The Ci (charged plus uncharged) was 1.5 times greater than the uncharged form of administered lidocaine. The changes in pHi depended on the increase in Ci. The AP disappeared only after administration of high pH lidocaine solutions (pH = 7.8, 9.0) and reappeared by washing out the solution in the chamber. Nerve block occurred more rapidly at pH 9.0 than at pH 7.8, and the time after washing out the lidocaine was longer at pH 9.0 than at pH 7.8. The mean Ci and charged lidocaine concentration in the axoplasm, when the AP disappeared or reappeared, were lower at pH 9.0 than at pH 7.8 (P < 0.05). CONCLUSION: Uncharged lidocaine penetrates the axon membrane to the axoplasm where it changes to the charged form and is concentrated in the axon membrane and axoplasm. External application of uncharged lidocaine plays a role in modulating nerve conduction.

Barotropic phase transitions of dioleoylphosphatidylcholine and stearoyl-oleoylphosphatidylcholine bilayer membranes.

In order to understand the effect of cis unsaturation on the thermotropic and barotropic phase behavior of phospholipid bilayer membranes, the phase transitions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) bilayer membranes were observed by high-pressure optical method. With respect to DOPC bilayer membrane, the so-called main transition between the liquid crystalline (Lalpha) and the lamellar gel (Lbeta) phases was observed in water at above 0 degrees C under high pressure, in addition to the transition between the Lalpha and the lamellar crystalline (L(C)) phases in 50% aqueous ethylene glycol. The pressure of main transition increased linearly with an increase in temperature. Extrapolation of temperature (T)-pressure (P) phase boundary to ambient pressure suggests the temperature of the main transition to be -40.3 degrees C, which has never been found by the DSC method. On the other hand, the temperature of L(C)/Lalpha phase transition in 50% aqueous ethylene glycol was found to be -12.0 degrees C at ambient pressure. The main transition temperatures for DSPC, SOPC and DOPC are 55.6, 6.7 and -40.3 degrees C, respectively, at ambient pressure. The substitution of cis unsaturated chain for saturated chains of DSPC brings about the depression of the main transition temperature by about 48 (+/-1) degrees C for each chain. The volume changes (deltaV) associated with the transitions were calculated from the transition enthalpy (deltaH) and the slope of T-P diagram (dT/dP) by means of the Clapeyron-Clausius equation. The value of deltaV for the main transition of SOPC bilayer membranes was reduced to half the volume change for DSPC bilayers, which means the introduction of the cis double bond in the acyl chain of lipids brings about the reduction of deltaV because of the disordered packing of unsaturated chains in the gel phase of lipid bilayer membranes.

Barotropic phase transitions and pressure-induced interdigitation on bilayer membranes of phospholipids with varying acyl chain lengths.

The bilayer phase diagrams of a series of 1, 2-diacylphosphatidylcholines containing linear saturated acyl chain (C=13, 14, 15, 16, 17 and 18) were constructed by two kinds of high-pressure optical methods. One is the observation of isothermal barotropic phase transition and the other is the isobaric thermotropic phase transition. The temperature of the main transition from the ripple gel (Pbeta') phase to the liquid crystal (Lalpha) phase for each lipid was elevated by pressure. The slope of the temperature-pressure diagram, dT/dP, was in the range of 0.21-0. 23 K MPa-1 depending on the acyl chain length. The temperature of the pretransition from the lamellar gel (Lbeta') phase to the Pbeta' phase for each lipid was also elevated by pressure. The slope of phase boundary, dT/dP, for the pretransition was in the range of 0. 12-0.14 K MPa-1. Both temperatures of the main and pretransition under ambient pressure increased with an increase in acyl chain length. The chain length dependences of the pretransition and main transition temperatures describe smooth curves with no evidence of odd/even discontinuities. Pressure-induced interdigitated gel (LbetaI) phase was observed beyond 300 MPa for 14:0-PC, 175 MPa for 15:0-PC, 100 MPa for 16:0-PC, 80 MPa for 17:0-PC and 70 MPa for 18:0-PC, respectively. The minimum pressure for the interdigitation of lipid bilayer membranes decreased with an increase in acyl chain length in a manner of non-linear relation. The slopes of phase boundary between Lbeta' and LbetaI phases transformed from the negative slope to the positive slope as the pressure increases.

Membrane-buffer partition coefficients of a local anesthetic tetracaine monitored by an anesthetic sensor; effects of temperature and pH.

Binding of a local anesthetic tetracaine (TC) to dimyristoylphosphatidylcholine (DMPC) bilayer membrane was studied by the potentiomerty with an ion-selective electrode sensitive to TC cation. DMPC membrane-buffer partition coefficient (K(app)) was determined in mole fraction unit as a function of pH for the lamellar gel (at 12 degrees C), ripple gel (at 20 degrees C), and liquid crystal (at 30 degrees C) phases. The partition coefficients of charged (K+) and uncharged TC (K0) into the DMPC membranes were estimated from the pH-dependence of K(app). The three states of DMPC membranes were more receptive to the uncharged TC than the charged species.

Extremely Strong Interaction of Sodium Decyl Sulfate and Decyltrimethylammonium Bromide in Molecular Aggregates

The thermodynamic behavior of a mixture of sodium decyl sulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) in aqueous solution and in molecular aggregates such as surface adsorbed films and micelles was investigated by measuring the electric conductivity and surface tension of the aqueous solutions. The thermodynamic quantities in solution and those in the molecular aggregates were evaluated from the experimental conductivity and surface tension data. The results for molar conductivity showed that dimerization or ion-pair formation of the SDeS and DeTAB molecules does not occur in aqueous solution and the mixture behaves as uni-univalent strong electrolyte below the critical micelle concentration (CMC). Contrary to the results in the aqueous solution, we found significant nonideal behavior in the phase diagrams of surface adsorption; that is, equimolar mixture of SDeS and DeTAB exists in the adsorbed film at almost all compositions irrespective of the bulk composition in the solution. The same result was also observed in the phase diagram of micelle formation. There was no difference in phase diagrams between surface adsorption and micelle formation at the CMC. The great nonideal mixing of SDeS and DeTAB in the molecular aggregates is undoubtedly attributable to the extreme attractive interaction between oppositely charged polar head groups of surfactants as well as to cohesion between hydrophobic groups. Further, in a low concentration region, it turned out that equimolar composition is preserved in the film during phase transition of the mixed adsorbed film of SDeS and DeTAB from a gaseous state to an expanded state.

Effects of pressure and local anesthetic tetracaine on dipalmitoylphosphatidylcholine bilayers.

The temperature-pressure phase diagram of dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles was constructed in the presence of a local anesthetic tetracaine hydrochloride (TC-HCl). The phase-transition temperatures under various pressures were determined by the method of high-pressure light transmission. The temperature of the main transition from the ripple gel (P'(beta)) to the liquid crystal (L(alpha)) phase was depressed by the addition of TC-HCl and elevated by application of pressure up to 150 MPa. The temperature of the pretransition from the lamellar gel (L'(beta)) to the P'(beta) phase was also depressed by the addition of TC-HCl below ca. 10.0 mmol kg(-1) and elevated by the pressure below ca. 50 MPa. Therefore, pressure-anesthetic antagonism for both phase-transitions was confirmed. The pressure-induced interdigitated gel (L(beta)I) phase has been observed under high pressure above 100 MPa in the absence of TC-HCl. The L(beta)I phase is known to be induced also by a variety of small amphiphilic molecules such as ethanol, benzyl alcohol and TC-HCl. In the presence of TC-HCl ranging in concentration up to 20.0 mmol kg(-1), the L(beta)I phase instead of the P'(beta) phase appeared at higher pressure. Present results revealed that pressure facilitates, rather than antagonizes, the effect of TC-HCl on the occurrence of interdigitated gel phase. Furthermore, two regions of two phase coexistence were observed under high pressure in the presence of TC-HCl. One is probably a region of coexisting L(beta)I and L(alpha) phase, which was found between L(beta)I and L(alpha) phases under various pressures. The other is probably a region of coexisting L'(beta) and L(beta)I phase, which was observed in the presence of TC-HCl up to 10.0 mmol kg(-1) at the pressure above 40 MPa and at the temperature below ca. 35 degrees C.

Thermotropic and barotropic phase behavior of dihexadecylphosphatidylcholine bilayer membrane.

The temperature (T)-pressure (P) phase diagram of the ether-linked dihexadecylphosphatidylcholine (DHPC) multilamellar vesicles was constructed by the method of high-pressure optical density. The DHPC membrane at ambient pressure undergoes the pretransition (at 33.6 degrees C) from the interdigitated gel (L beta I) phase to the ripple gel (P' beta) phase, and succeedingly the main transition (at 44.4 degrees C) from the P' beta phase to the liquid crystal (L alpha) phase. Since the slope of the T-P diagram for the pretransition, 0.316 K MPa-1, is larger than that for the main transition, 0.242 K MPa-1, the phase boundary between P' beta and L beta I phases disappeared at high pressure above 130 MPa. A triple point among L beta I, P' beta and L alpha phases was found at 130 MPa and 74.5 degrees C. Difference in phase diagrams between the ether-linked and ester-linked phospholipid bilayer membranes has been elucidated.

Local anesthetic-sensitive electrodes: preparation of coated-wire electrodes and their basic properties in vitro.

Coated-wire electrodes with local anesthetic (LA) cation-selective membranes were prepared, and their properties in vitro were investigated. Copper wires (0.8-mm diameter) were coated with gel membranes of 110 mg of poly(vinyl chloride), 5 mg of ion pairs of tetraphenylborate anion with LA cation, 100 mg of dioctylphtalate, and 1.5 mL of tetrahydrofuran. This was the composition determined to be most suitable. Their electromotive force relative to an Ag/AgCl electrode was measured in LA solutions. The lidocaine, dibucaine, and mepivacaine electrodes all showed good Nernstian response at 25 degrees C in aqueous solutions in the concentration ranges of 1 x 10(-4) to 1 x 10(-2) mol/L, 4 x 10(-5) to 1 x 10(-2) mol/L, and 5 x 10(-5) to 1 x 10(-2) mol/L, respectively. The response time was within 10 s. The electrode potential decreased as the pH in the solution increased, with a corresponding decrease of the protonated form of LA. The hydrophobic nature of the LA was closely related to the electromotive force and to the selectivity of the electrode toward various LA cations. Dibucaine, the most hydrophobic, had the highest electrode potential. The more hydrophobic the LA of the electrode, the less it is interfered with by other LA molecules. The more hydrophobic the interferent cation, the more it acts on the electrode potential. The electrode system could also measure LA in human plasma at 37 degrees C, although the responsiveness was depressed in the low concentration range owing to binding of LA to the serum protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzyl alcohol penetration into micelles, dielectric constant of the binding site, partition coefficient and high-pressure squeeze-out.

The absorbance maximum, lambda max, of a local anesthetic, benzyl alcohol, is shifted to longer wavelengths when solvent polarity is decreased. The shift was approximately a linear function of the dielectric constant of the solvent. This transition in electronic spectra according to the microenvironmental polarity is used to analyze benzyl alcohol binding to surfactant micelles. A facile method is devised to estimate the micelle/water partition coefficient from the dependence of lambda max of benzyl alcohol on surfactant concentrations. The effective dielectric constants of the sodium decyl sulfate, dodecyl sulfate and tetradecyl sulfate micelles were 29, 31 and 33, respectively. The partition coefficient of benzyl alcohol between the micelles and the aqueous phase was 417, 610 and 1089, respectively, in the mole fraction unit. The pressure dependence of the partition coefficient was estimated from the depression of the critical micelle concentration of sodium dodecyl sulfate by benzyl alcohol under high pressure up to 200 MPa. High pressure squeezed out benzyl alcohol molecules from the micelle until about 120 MPa, then started to squeeze in when the pressure was further increased. The volume change of benzyl alcohol by transfer from the aqueous to the micellar phase was calculated from the pressure dependence of the partition coefficient. The volume change, estimated from the thermodynamic argument, was 3.5 +/- 1.1 cm3.mol-1 at 298.15 K, which was in reasonable agreement with the partial molal volume change determined directly from the solution density measurements, 3.1 +/- 0.2 cm3.mol-1. Benzyl alcohol apparently solvates into the micelles close to surface without losing contact with the aqueous phase.

Interfacial adsorption of an inhalation anesthetic onto ionic surfactant micelles and its desorption by high pressure.

The effects of pressure and temperature on the critical micelle concentration (CMC) of sodium dodecylsulfate (SDS) wer measured in the presence of various concentrations of an inhalation anesthetic, methoxyflurane. The change in the partial molal volume of SDS on micellization delta Vm, increased with the increase in the concentration of methoxyflurane. The CMC-decreasing power, which is defined as the slope of the linear plot between In(CMC) vs. mole fraction of anesthetic, was determined as a function of pressure and temperature. Since the CMC-decreasing power is correlated to the micelle/water partition coefficient of anesthetic, the volume change of the transfer (delta Vop) of methoxyflurane from water to the micelle can be determined from the pressure dependence of the CMC-decreasing power. The value of delta Vop amounts 6.5 +/- 1.8 cm3.mol-1, which is in reasonable agreement with the volume change determined directly from the density data, 5.5+/-0.6 cm3.mol-1. Under the convention of thermodynamics, this indicates that the application of pressure squeezes out anesthetic molecules from the micelle. The transfer enthalpy of anesthetic from water to the micelle is slightly endothermic. The partial molal volume of methoxyflurane in the micelle (112.0 cm3.mol-1) is smaller than that in decane (120.5 cm3.mol-1) and is larger than that in water (108.0 cm3. mol-1. This indicates that the anesthetic molecules are incorporated into the micellar surfaces region, i.e., the palisade layer of the micelle in contact with water molecules, rather than into the micelle core.

Partition equilibrium of inhalation anesthetics and alcohols between water and membranes of phospholipids with varying acyl chain-lengths.

From the depression of the phase-transition temperature of phospholipid membranes, the partition coefficients of inhalation anesthetics (methoxyflurane, halothane, enflurane, chloroform and diethyl ether) and alcohols (benzyl alcohol and homologous n-alcohols up to C = 7) between phospholipid vesicle membranes and water were determined. The phospholipids used were dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines. It was found that the difference in the acyl chain length of the three phospholipids did not affect the partition coefficients of the inhalation anesthetics and benzyl alcohol. The actions of these drugs are apparently directed mainly to the interfacial region. In contrast, n-alcohols tend to bind more tightly to the phospholipid vesicles with longer acyl chains. The absolute values of the transfer free energies of n-alcohols increased with the increase of the length of the alkyl chain of the alcohols. The increment was 3.43 kJ per each carbon atom. The numerical values of the partition coefficients are not identical when different expressions for solute concentrations (mole fraction, molality and molarity) are employed. The conversion factors among these values were estimated from the molecular weights and the partial molal volumes of the phospholipids in aqueous solution determined by oscillation densimetry.

Pressure-anesthetic antagonism on the phase separation of non-ionic surfactant micelles.

An aqueous solution of non-ionic surfactants becomes suddenly turbid when heated to a critical temperature, known as the cloud point, and concomitantly expands the volume. The volume expansion is caused by release of structured water molecules from the hydrophilic polyoxyethyelene moieties. Inhalation anesthetics decreased the cloud-point temperature of hexaoxyethylene dodecyl ether micelles. The concentrations of methoxyflurane, halothane and enflurane causing a 1 degree C depression of the cloud-point temperature were 0.51, 0.71 and 0.78 mmolal, respectively. Hydrostatic pressure increased the cloud-point temperature in the absence and presence of the anesthetics. The change of the apparent molal volume at the cloud point was estimated to be 2.2 cm3/mol in the absence of anesthetics. This value decreased in the presence of the anesthetics, dose dependently. The results indicate that the anesthetics favor dehydration of the hydrophilic surface of the non-ionic surfactant micelles.