Effects of n-alkanols on the membrane fluidity of chick embryo heart microsomes

Thermodynamic and structural study of DMPC-alkanol systems

The thermodynamic and structural behaviors of lamellar dimyristoylphosphatidylcholine-alkanol (abbreviation DMPC-CnOH, n = 8-18 is the even number of carbons in the alkyl chain) systems were studied by using DSC and SAXD/WAXD methods at a 0-0.8 CnOH : DMPC molar ratio range. Up to n≤ 10 a significant biphasic effect depending on the main transition temperature t_m on the CnOH concentration was observed. Two breakpoints were revealed: turning point (TP), corresponding to the minimum, and threshold concentration (c_T), corresponding to the end of the biphasic tendency. These breakpoints were also observed in the alkanol concentration dependent change in the enthalpy of the main transition ΔH_m. In the case of CnOHs with n > 10 we propose a marked shift of TP and c_T to very low concentrations; consequently, only increase of t_m is observed. A partial phase diagram was constructed for a pseudo-binary DMPC-C12OH system. We suggest a fluid-fluid immiscibility of the DMPC-C12OH system above c_T with a consequent formation of domains with different C12OH contents. At a constant CnOH concentration, the effects of CnOHs on ΔH_m and bilayer repeat distance were found to depend predominantly on the mismatch between CnOH and lipid chain lengths. Observed effects are suggested to be underlined by a counterbalancing effect of interchain van der Waals interactions and headgroup repulsion.

General anesthetic octanol and related compounds activate wild-type and delF508 cystic fibrosis chloride channels

1. Cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel is defective during cystic fibrosis (CF). Activators of the CFTR Cl(-) channel may be useful for therapy of CF. Here, we demonstrate that a range of general anesthetics like normal-alkanols (n-alkanols) and related compounds can stimulate the Cl(-) channel activity of wild-type CFTR and delF508-CFTR mutant. 2. The effects of n-alkanols like octanol on CFTR activity were measured by iodide ((125)I) efflux and patch-clamp techniques on three distinct cellular models: (1). CFTR-expressing Chinese hamster ovary cells, (2). human airway Calu-3 epithelial cells and (3). human airway JME/CF15 epithelial cells which express the delF508-CFTR mutant. 3. Our data show for the first time that n-alkanols activate both wild-type CFTR and delF508-CFTR mutant. Octanol stimulated (125)I efflux in a dose-dependent manner in CFTR-expressing cells (wild-type and delF508) but not in cell lines lacking CFTR. (125)I efflux and Cl(-) currents induced by octanol were blocked by glibenclamide but insensitive to 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, as expected for a CFTR Cl(-) current. 4. CFTR activation by octanol was neither due to cell-to-cell uncoupling properties of octanol nor to an intracellular cAMP increase. CFTR activation by octanol requires phosphorylation by protein kinase-A (PKA) since it was prevented by H-89, a PKA inhibitor. 5. n-Alkanols chain length was an important determinant for channel activation, with rank order of potencies: 1-heptanol<1-octanol<2-octanol<1-decanol. Our findings may be of valuable interest for developing novel therapeutic strategies for CF.

Solvent effects on squid sodium channels are attributable to movements of a flexible protein structure in gating currents and to hydration in a pore

1. Solvent effects on the time course of gating and sodium currents were analysed in squid sodium channels using four non-electrolytes of different size, glycerol, erythritol, glucose and sucrose, to separate effects of viscosity from those of osmolarity and to obtain viscosity and osmolarity parameters that were independent of molecular size. 2. The gating and sodium currents were reversibly slowed in a voltage-independent manner as the non-electrolyte concentration increased. 3. Solvent effects were analysed using a model in which the percentage change in time constant was expressed by an equation involving the viscosity parameter alpha and the osmolarity parameter delta: t/t0 = alpha (eta/eta 0) - 1 + 100 alpha-1)exp(delta delta pi), where eta/eta 0 is solution viscosity and delta pi is increase in osmolarity. Since the solution viscosity was found experimentally to be a function of the solution osmolarity, solvent effects are described by an equation with one independent variable eta/eta 0 or delta pi. 4. Voltage sensor movement, reflected in gating currents, was primarily sensitive to viscosity, as its decay time constant was a function of eta/eta 0, with only a minor sensitivity to osmolarity (delta was 2-3 water molecules). 5. For sodium currents, alpha was equal to that of gating currents but delta was 2-3 times greater, suggesting that the final channel opening was primarily sensitive to osmolarity (delta delta was 5 water molecules). The relative ineffectiveness of the largest non-electrolyte, sucrose, suggested that this osmolarity-sensitive step in channel opening occurred in the narrow pore region. 6. Sodium channel inactivation was primarily sensitive to osmolarity (delta delta was 8-12 water molecules). 7. The observed viscosity dependence of the sodium current activation and inactivation processes was attributable to the viscosity-dependent process accompanying the gating current. 8. This model explains why non-electrolytes slow sodium currents while electrolytes do not. 9. Viscosity effects on gating currents can be explained by a process in which non-electrolytes interact with the flexible hydrophilic parts of sodium channel proteins, but osmolarity effects on the final step need to be explained by a local interaction of several water molecules with fluctuating protein segments in the pore.

Influence of the permeation enhancers 1-alkyl-2-pyrrolidones on permeant partitioning into the stratum corneum

In a previous study, the enhancing effects of a series of 1-alkyl-2-pyrrolidones (APs; 1-ethyl, 1-butyl, 1-hexyl, and 1-octyl-2-pyrrolidone) on the transport of steroidal permeants across hairless mouse skin were investigated via a parallel pathway skin model. Isoenhancement concentration conditions were deduced under which different APs induce essentially the same transport enhancement for the lipoidal pathway of the stratum corneum (s.c.). As a continuing effort to understand the mechanism of action of permeation enhancers, the influence of the APs on permeant partitioning into hairless mouse s.c. was investigated under the isoenhancement concentration conditions using beta-estradiol (E2 beta) as the model permeant. The amount of E2 beta uptake into s.c. was found to be essentially the same for all the APs under these isoenhancement conditions. This result suggests that inducing a higher partitioning tendency for E2 beta into the lipoidal pathway of hairless mouse s.c. is a principal mechanism of action of the APs in enhancing transdermal transport. The uptake of the APs into s.c. lipoidal domains was also determined, and the results show only a modest (approximately 2-fold) increase in the uptake of the APs in going from 1-ethyl-to 1-octyl-2-pyrrolidone under isoenhancement conditions. This indicates the potency of the APs as permeation enhancers is only very modestly dependent upon the alkyl chain length in this chain length region when compared at concentrations in the microenvironment where the action occurs in the lipid domains.

Correlation between the n-alkanols-induced sensitization of erythrocytes to hyperthermia and the fluidization of their membrane

It was reported recently that the thermohaemolysis of mammalian erythrocytes is related to a thermo-induced membrane event of permeability barrier impairment in which the inactivation of membrane proteins is implicated. Here, the influence of different n-alkanols, methanol to octanol, on the onset temperature Tm of this barrier impairment event was compared with the changes in the dynamic properties of the membrane lipid region for human erythrocytes. The potencies of these n-alkanols to decrease Tm, to fluidize and disorder the lipid region were strongly related to their lipid solubilities. With respect to their membrane concentration, all the applied n-alkanols were roughly equipotent in decreasing Tm and in fluidizing and disordering the membrane lipids. Since Tm corresponds to the stability of erythrocytes against hyperthermia, this result indicates that the heat sensitization of these cells, induced by the n-alkanols employed, strongly correlated the fluidization (disordering) of the lipid region of their membranes.

Effect of phospholipids and organic solvents on the formation of 5,16-androstadien-3 beta-ol from pregnenolone in adrenal and testicular microsomes

The formation of 5,16-androstadien-3 beta-ol from pregnenolone (andien-beta synthase activity) is catalyzed by cytochrome P450c17, which also catalyzes C-17-hydroxy/lyase activity in the biosynthesis of androgens. Andien-beta synthase is very active in porcine Leydig cells, but it is almost undetectable in porcine and bovine adrenal, although the adrenal gland also expresses P450c17. We have treated microsomal preparations with lipids and organic solvents to examine if the andien-beta synthase and C-17-hydroxy/lyase activities of P450c17 were affected by these agents. The addition of some phospholipids to the microsomal preparations inhibited both P450c17 activities. Phospholipids with different fatty acids had no effect on the ratio of andien-beta synthase to C-17-hydroxy/lyase activity. The addition of solvents to the microsomal preparations generally inhibited both P450c17 activities. However, the addition of acetyl acetone up to 5% (v/v) preferentially increased the andien-beta synthase activity while decreasing, the C-17-hydroxy/lyase activity. The effect was dose-dependent, specific to acetyl acetone and was seen in both testis and adrenal microsomes. The exact nature of the stimulation of andien-beta synthase activity is unknown, but the andien-beta synthase activity obtained after treatment with acetyl acetone was directly correlated to total P450c17 activity in the untreated microsomes. The inhibition of C-17-hydroxy/lyase activity by acetyl acetone was particularly apparent with the C-17,20-lyase reaction rather than the 17 alpha-hydroxylase reaction. The addition of acetyl acetone can potentially be used to assess the total potential of P450c17 to catalyze andien-beta synthase activity in vitro.

Hexanol and lidocaine affect the oligomeric state of the Ca-ATPase of sarcoplasmic reticulum

Hexanol at 7 degrees C stimulates the activity of the Ca-ATPase of sarcoplasmic reticulum (SR). Time-resolved phosphorescence spectroscopy studies of SR whose Ca-ATPase is covalently labeled with erythrosin isothiocyanate (ERITC) indicate that at 7 degrees C hexanol (1) cause a concentration-dependent increase in the rate of decay of phosphorescence anisotropy, (2) causes larger oligomers of Ca-ATPase to dissociate into smaller oligomers, and (3) increases the rotational mobility of Ca-ATPase in all its oligomeric states. Electron paramagnetic resonance (EPR) spectroscopy of spin-labeled stearic acid (SASL) in SR suggests that at 7 degrees C hexanol diminishes the fraction of SR lipids in the boundary lipid domain and disorders and fluidizes both the boundary lipid and the unrestricted lipid domain. In protein-free liposomes of extracted SR lipids hexanol increases fluidity and decreases order to a greater extent near the center of the lipid bilayer than near the polar head groups. At 25 degrees C hexanol has biphasic effects on Ca-ATPase activity: at 10 and 20 mM hexanol increases activity, but at 30 mM and especially at 40 mM there is inhibition of Ca-ATPase activity. The influence of hexanol at 25 degrees C on the oligomeric state of Ca-ATPase is also biphasic. At 10 and 20 mM, hexanol promotes the dissociation of larger oligomers into smaller ones, whereas at higher concentrations, 30 and 40 mM, hexanol causes larger oligomers to be formed from smaller ones. Lidocaine at 25 degrees C inhibits Ca-ATPase activity and causes dramatic slowing of the decay of phosphorescence anisotropy of ERITC-labeled SR by causing the formation of larger oligomers of Ca-ATPase from smaller ones. In protein-free liposomes of SR lipids at 25 degrees C, lidocaine disorders and fluidizes the acyl chains near the center of the bilayer (as did hexanol), but has opposite effects near the polar head groups. The opposite effects of hexanol and lidocaine on the oligomeric state of the SR Ca-ATPase provide a new molecular explanation for the opposite effects of hexanol and lidocaine on the activity of the Ca-ATPase. We conclude that the biphasic effects of hexanol on the activity of Ca-ATPase can be accounted for by biphasic effects of hexanol on the oligomeric state of the Ca-ATPase. This study supports the view that anesthetics can alter interactions between membrane proteins.

Fluidity of the microsomal membrane and cytochrome P450 reduction kinetics of pig liver microsomes as a consequence of organic solvent impact

1. The effect of the aromatic solvents toluene, xylene and ethylbenzene on microsomal membrane fluidity and anaerobic NADPH-reduction kinetics were studied. 2. The relation of membrane fluidity to the kinetics of cytochrome P450 reduction by NADPH-cytochrome P450 reductase was examined with regard to a membrane-mediated molecular organization of the multienzyme components of the monooxygenase system. 3. Membrane fluidity changes were detected with the steady-state pyrene excimer formation method and with fluorescence lifetime measurements after incubation of the microsomes with organic solvents. 4. Increase in membrane fluidity in presence of organic solvents leads to a small but significant decrease of the rate constant of the cytochrome P450 reduction kinetics and a change in the relative amplitudes of the components of the biphasic response. 5. The results support the idea of a molecular organization of cytochrome P450 in clusters. Fluidization of the microsomal membrane by organic solvents increase the cytochrome P450 cluster formation.

Effect of organic solvents on nervous cell membrane as measured by changes in the (Ca2+/Mg2+) ATPase activity and fluidity of synaptosomal membrane

The effect of various solvents on the central nervous system was studied by using rat brain synaptosomal membranes as an in vitro model. The activity of (Ca2+/Mg2+) ATPase and the membrane fluidity was determined. The alteration of the ATPase activity depended on the physio-chemical characteristics of the solvent in question. Incubation with aliphatic alkanes caused a stimulation of the ATPase activity whereas mixed hydrocarbons as kerosene, white spirit and gasoline inhibited the enzyme. Incubation with chlorinated hydrocarbons caused a biphasic response dependent on the concentration. Oxygen-containing hydrocarbons exhibited various effects as found after incubation with hydrocarbons. The different effects of the solvents on the ATPase activity suggest that the lipophilicity of the solvents is one of more parameters affecting the membrane. Furthermore, the biphasic response following the incubation with chlorinated hydrocarbons indicates that more mechanisms are involved in the enzyme effect. The membrane fluidity is increased with higher concentrations of the solvents. From the results it is concluded that the ATPase activity depends not only on the membrane fluidity and volume, but also on the hydrophilic vicinity of the enzyme molecule.

Influence of phloretin and alcohols on barrier defects in the erythrocyte membrane caused by oxidative injury and electroporation

Oxidative damage by diamide, periodate and oxygen-derived reactive species, but also exposure to electroporation induce in the erythrocyte membrane dynamic, presumably fluctuating, defects having the properties of aqueous holes with definable radii and selectivities. These leaks, which can be quantified by measuring tracer fluxes or rates of colloid-osmotic lysis, are here shown to be inhibited by phloretin and a small number of related phenol compounds (phenolphthalein, hydroxyacetophenones, nitrophenol), while a host of other 'membrane-active' agents is not effective in this respect. I50 values range from about 200 microM for phloretin and phenolphthalein to about 10 mM for 4-nitrophenol. Inhibition by phloretin is reversible, not competitive and not related in its extent to the extent of leakiness. In contrast, the enhancement of transbilayer mobility of amphiphilic lipid probes, which invariably goes along with leak formation of the type described, is not affected by phloretin. Aliphatic alcohols (hexanol, butanol) have an amplifying effect on leaks induced by oxidative damage but do not affect leaks induced by electroporation. The alcohol-amplified leaks maintain the properties of aqueous holes as indicated by a low activation energy of leak fluxes. Since both, inhibition and stimulation of leak fluxes do not go along with appreciable changes of the apparent radii of the aqueous holes, changes in the dynamics (opening and closing) of the defects are proposed to underly the effects of phloretin and alkanols. The membrane lipid domain is likely to be the site of the leaks and of their modulation.

The effects of alcohols in vitro on the nervous cell membrane measured by changes in the (Ca2+/Mg2+) ATPase activity and fluidity of the synaptosomal membrane

The effect of various alkanols on the central nervous system was studied by using rat brain synaptosomal membranes as an in vitro model. The activity of (Ca2+/Mg2+)ATPase and the membrane fluidity were determined. The n-alkanols exhibited an increased molar inhibition of the ATPase activity with an increase in the carbon chain length up to 1-octanol. 1-octanol and 1-decanol caused a biphasic effect on the ATPase activity depending on the alkanol concentration, whereas 1-dodecanol caused a stimulation of the ATPase activity. All alkanols studied caused an increased fluidity of the membrane. Our results indicate that the effect of alkanols on the ATPase activity depends on changes in the border layer between the membrane and the surrounding medium and on a binding of the alkanols to the enzyme molecule. Furthermore, the two-way effect of 1-octanol and 1-decanol and the stimulatory effect of 1-dodecanol indicate that more mechanisms are involved. In addition, the results indicate that changes in the membrane fluidity do not seem to be a prerequisite of the ATPase inhibition.

The susceptibility of membrane vesicles to interaction with ethanol

The susceptibility of membranes to interaction with ethanol is an important consideration in the further understanding of the ethanol-membrane interaction. Interaction of membrane vesicles, including passive diffusion of ethanol across membranes, leakage of internal molecules out of membranes and membrane-membrane interaction, were examined systematically using two populations of fluorescent probe-encapsulated phospholipid bilayer vesicles, each prepared with 1,2-dimyristoyl phosphatidylcholine, cholesterol and a fluorescent probe. Fluorescence quenching experiments with these vesicles were performed in a medium containing a wide range of ethanol concentrations (0.30-3.5 M). In the presence of a lower concentration of ethanol in the external medium, passive diffusion of ethanol across membrane vesicles occurred. This was demonstrated by an interaction of ethanol with the encapsulated fluorescence probe molecules inside the vesicles, resulting in an increase in the fluorescence intensity and a shift of the fluorescence emission spectrum to a shorter wavelength. While, in the presence of a higher concentration of ethanol in the external medium, a strong perturbation of lipid bilayers by ethanol was found, leading to an over expansion of membranes and consequently causing the membrane leakage. As a result of this, the initially encapsulated probe molecules leaked out of the vesicles so as to interact with the other probe molecules in the external medium. Consequently, fluorescence quenching was observed. Moreover, studies of the mixture of two populations of fluorescence probe-encapsulated membrane vesicles revealed that ethanol acted on individual membranes and did not promote membrane-membrane interactions. The implication of the present results to the alcohol-mediated expansion of membranes is discussed.

Uncoupling of cardiac cells by doxyl stearic acids specificity and mechanism of action

The influence of doxyl stearic acids (DSAs) on gap junctional conductance (gj) between pairs of neonatal rat heart cells was studied. DSAs are spin probes that perturb the membrane at different depths depending on position of the doxyl group on the fatty acyl chain. 16-DSA and 12-DSA rapidly and reversibly reduced gj to unmeasureable levels in a dose- and time-dependent manner. Single channel events observed when gj was low were of the same unitary size as those observed under control conditions. The methyl esters of 16- and 12-DSA, stearic acid itself, and TEMPO, an analogue of the doxyl group that has no fatty acyl chain, had no effect on gj. Protonation of the carboxyl head group (by acidifying the solution) reduced the potency of 16- or 12-DSA. Spontaneous beating activity and action potentials were observed at concentrations of the DSAs 15-20 times that necessary for uncoupling. These results indicate that uncoupling by the DSAs requires the presence of the charged carboxyl group and localized perturbation of the channel at the lipid-channel interface by the doxyl group. Furthermore, they predict that unsaturated free fatty acids, which accumulate during ischemia, may exert their arrhythmogenic effect by reducing gj, and thereby slowing conduction.

The interaction of ethanol and exogenous arachidonic acid in the generation of extracellular messengers by mouse peritoneal macrophages

It is increasingly recognized that macrophages play a crucial role in the development of chronic inflammatory states such as alcoholic liver disease. These cells can metabolize free arachidonic acid in the absence of a discernible trigger. The present study was undertaken to examine the short-term effects of ethanol on the generation of these exogenous arachidonate-derived extracellular mediators. Ethanol caused a dose-dependent decrease in the production of both cyclooxygenase and lipoxygenase metabolites. Similar effects were observed on the esterification of exogenous arachidonate into cellular lipids. To characterize further the effects of ethanol on exogenous arachidonic acid metabolism, we studied the short-term responses displayed by macrophages challenged with another soluble stimulus; the tumor-promoting agent phorbol myristate acetate. We observed an inhibition by ethanol of the superoxide anion response triggered by phorbol myristate acetate similar to that observed for exogenous arachidonate oxygenation. Our results show that ethanol can inhibit these soluble stimuli-elicited responses, possibly through its disorganizing effect on plasma membrane.

The interaction of n-alkanols with lipid bilayer membranes: a 2H-NMR study

The interaction of eight n-alkanols with bilayers of dimyristoylphosphatidylcholine (DMPC) has been studied by deuterium nuclear magnetic resonance (2H-NMR). At comparable temperatures and concentrations of solute in the bilayer, order parameters measured at the 1-methylene segment of the n-alkanols show a maximum for n-dodecanol. For both n-dodecanol and n-tetradecanol, orientational ordering shows a maximum at the C-4 to C-7 methylene segments, with labels at both ends of the n-alkanol exhibiting reduced order. These observations are consistent with earlier findings for n-octanol and n-decanol. Unlike the longer chain n-alkanols, ordering in n-butanol decreases from the hydroxyl group end to the methyl group end of the molecule. Orientational ordering at nine inequivalent sites in DMPC, has also been measured as a function of temperature, for bilayers containing n-butanol, n-octanol, n-dodecanol and n-tetradecanol. At the 3R,S sites on the glycerol backbone, for comparable temperatures and solute concentrations, n-butanol produces a larger disordering than the other n-alkanols. This result probably reflects the greater fraction of time spent by the hydroxyl group of n-butanol in the vicinity of the lipid polar head group compared with the hydroxyl group in longer chain n-alkanols. It was found that n-octanol orders the acyl chains of DMPC, unlike n-butanol which disorders them, and the longer chain n-alkanols which have little effect. Within experimental error, the effect of n-dodecanol on order at all sites in DMPC is the same as n-tetradecanol. The influence of n-alkanols on DMPC ordering at twelve sites has been compared with that of cholesterol which is shown to interact with DMPC bilayers in a distinctly different manner from the n-alkanols.

Interaction of surfactants with vesicle membrane of dipalmitoylphosphatidylcholine: fluorescence depolarization study

The effect of surfactants on the "fluidity" of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was studied by means of the fluorescence depolarization technique with fatty acid fluorescent probes, in which the anthroyloxy group is introduced at different positions along the acyl chain. Three types of surfactants were examined; anionic sodium alkylsulfates, cationic alkyltrimethylammonium chlorides, and non-ionic alkanoyl-N-methylglucamides (MEGA-n). Perturbing effects of the surfactants depended on both the alkyl chain-length and the type of head group. Sodium alkylsulfates with octyl- and decyl-chain and alkyltrimethylammonium chlorides with octyl-, decyl- and dodecyl-chain did not affect the membrane fluidity when incorporated in the membrane, whereas sodium dodecylsulfate and tetradecyltrimethylammonium chloride decreased the membrane fluidity at both gel and liquid crystalline states of the membrane. All the MEGA series surfactants decreased the membrane fluidity, whose perturbing potency was in the order of MEGA-8 less than MEGA-9 approximately equal to MEGA-10. The perturbation at different depths in the membrane by sodium dodecylsulfate and MEGA-9 was also examined. No significant change in the fluidity gradient across the membrane was induced by the addition of these surfactants.

Effect of short-chain primary alcohols on fluidity and activity of sarcoplasmic reticulum membranes

Intramolecular excimer formation with the fluorescent probe 1,3-di(1-pyrenyl)propane, differential scanning calorimetry, and X-ray diffraction were used to assess the effect of ethanol, 1-butanol, and 1-hexanol on the bilayer organization in model membranes, sarcoplasmic reticulum (SR) lipids and native SR membranes. These alcohols have fluidizing effects on membranes and lower the main transition temperature of dimyristoylphosphatidylcholine (DMPC), but only 1-hexanol alters the cooperativity of the phase transition and significantly increases the thickness of DMPC bilayers. The interaction of the three alcohols with the SR Ca2+ pump was also investigated. Hydrolysis of ATP and coupled Ca2+ uptake are differently sensitive to the three alcohols. Whereas ethanol and 1-butanol inhibited the Ca2+ uptake, 1-hexanol stimulated it. Nevertheless, the energetic efficiency of the pump (Ca2+/ATP) is not significantly affected by ethanol or 1-hexanol, but uncoupling was observed with 1-butanol at high concentrations. The different effects of alcohols on the activity of SR membranes rule out an unitary mechanism of action on the basis of fluidity changes induced in the lipid bilayer. Depending on the chain length, the alcohols interact with the SR membranes in different domains, perturbing differently the Ca2+-pump activity.

Deuterium NMR study of the effect of n-alkanol anesthetics on a model membrane system

The effects of 25 mol% incorporation of two anesthetics, 1-octanol and 1-decanol, on a deuterated, saturated phospholipid in 50 wt% aqueous multilamellar dispersions have been studied by 2H-NMR spectroscopy and differential scanning calorimetry (DSC). The phospholipid used is sn-2 substituted '[2H31]-palmitoylphosphatidylcholine' (PC-d31). DSC thermograms demonstrate that PC-d31 has phase behavior qualitatively similar to that of dipalmitoylphosphatidylcholine, with a pretransition at 31 degrees C and a main gel to liquid crystalline transition at 40 degrees C. Analysis of the temperature-dependent 2H-NMR spectra in terms of the first moment, which is extremely sensitive to the phospholipid phase, shows that 1-octanol and 1-decanol depress and broaden the main transition. This is confirmed by DSC, which shows that the pretransition is eliminated by the 1-alkanols. The carbon-deuterium bond order of the phospholipid deuterated acyl chains, in the presence and absence of 1-alkanols, was determined from deuterium quadrupolar splittings. Spectra were analyzed using the depaking technique. A 1-alkanol concentration of 25 mol% had no significant effect on the profile of the carbon-deuterium bond order parameter SCD along the phospholipid acyl chain at 50 degrees C. Thus, it appears that the liquid crystalline phase is able to accommodate large amounts of linear anesthetic molecules without substantial effect on molecular ordering within the membrane bilayer. Preliminary results show that the transverse relaxation rates of the acyl chain segments are significantly decreased by the presence of 1-octanol or 1-decanol.

Perturbation of egg phosphatidylcholine and dipalmitoylphosphatidylcholine multilamellar vesicles by n-alkanols. A fluorescent probe study

The perturbing effects of n-alkanols (pentanol, decanol and tetradecanol) in egg phosphatidylcholine and dipalmitoylphosphatidylcholine multilamellar vesicles were studied with five fluorescent probes, 1-(4'-trimethylaminophenyl)-6-phenylhexa-1,3,5-triene (TMA-DPH), 1,6-diphenyl-1,3,5-hexatriene, and 2-, 7-, and 12-(9-anthroxyloxy)stearic acid (2-, 7-, and 12-AS). These probes localize at various depths in the membrane, enabling study of the membrane-order gradient. Phase-modulation fluorescence spectroscopy was used to measure steady-state anisotropies, excited-state lifetimes and differential polarized lifetimes from which the limiting hindered anisotropies (r infinity) and the logarithm of the rotational rate (log R) were calculated. The probes that localize at about the same depth in the membrane (TMA-DPH and 2-AS, diphenylhexatriene and 12-AS) generally, but not always, showed similar changes in r infinity and log R with added alkanols. However, the absolute values of r infinity and log R were usually different. The inconsistencies are attributed to differences in the probes' sizes, structures, photophysical properties and perturbing abilities. The perturbation of membranes by alkanols is chain-length-dependent. Pentanol disorders the membrane at all depths but is more effective in the membrane center than nearer to the polar headgroups of the phospholipids, tetradecanol can be accommodated into the membrane without effect or with increased order and the effects of decanol are intermediate between pentanol and tetradecanol. Our results with alkanols indicate that: a single perturber can have different effects on membrane order at different depths in the bilayer; the perturbation is observed at and distant from the perturbers' location in the membrane, and the bilayer center is more susceptible to perturbation by alkanols than the region of the bilayer near the phospholipid headgroups.

Thermodynamic interpretation of effects of alcohols on membrane lipid fluidity

The effect of a series of amphiphilic compounds, the first eight n-aliphatic alcohols, on the fluidity of rat enterocyte brush border was determined by ESR using 5-doxyl stearic acid as a lipid spin probe. Packing order variations are compared to the relative hydrophobic effect of the alcohols. The concentrations, [Ci]5 of each alcohol that decrease the membrane 2T' value by 5%, vary by a factor of 1500 from methanol to octanol. From [Ci]5, the membrane concentrations Cm and the variation of free energy delta F degree due to the incorporation of the alcohols in the lipids, were calculated. These calculations were performed taking into account the respective volumes of the aqueous phase and the membrane lipids. Cm is of the order of 0.18 mol/kg for the odd chain length alcohols and of 0.27 mol/kg for the even alcohols. The value of delta F degree in cal/mol -CH2- is -687 cal on average for the eight alcohols. This work shows that for all the alcohols, the concentrations at equilibrium in the membrane and in the aqueous phase are respectively in agreement with Meyer and Overton's theory and with the gradient of free energy which constitutes the most general index of interaction of lipophilic substances with membranes.

Comparison of the effect of temperature on kidney cortex mitochondria from rabbit, dog, pig, and human: Arrhenius plots of ADP-stimulated respiration

The effect of temperature on the rate of ADP-stimulated respiration of mitochondria from dog, rabbit, pig, and human kidney cortex mitochondria was plotted according to the Arrhenius relationship. The temperature at which the plot demonstrated a break was at 15 degrees C for mitochondria from dog, pig, and human kidneys. The discontinuity occurred at 10 degrees C or less for mitochondria from rabbit kidneys. This difference suggests that mitochondria from rabbit kidneys undergo a lipid-phase transition at lower temperatures than for other species commonly used in experimental renal preservation. The implications of this difference suggest caution in using results obtained with rabbit kidneys for comparison to results obtained from hypothermic renal preservation of other species kidneys. Apparent fluidization of dog kidney mitochondrial membranes with adamantine abolished the discontinuity in the Arrhenius plot.

Effects of anesthetic alcohols on membrane transport processes in human erythrocytes

1. Anesthetic alcohols (pentanol, hexanol and heptanol) were found to increase the fluidity of red cell membrane lipids as monitored by the fluorescence depolarization of diphenylhexatriene. The relative potency of the alcohols was found to be parallel to their relative membrane/water partition coefficients. 2. Hexanol had biphasic effect on erythritol uptake by simple diffusion by red cells. At concentrations less than 9 mM, there was an approximately linear increase in erythritol permeability with increasing alcohol concentration. 3. The facilitated transport of uridine was markedly inhibited by hexanol. Hexanol at 6 mM produced a 65% inhibition of uridine (4 mM) uptake. Hexanol decreased both the apparent Km and V values for the equilibrium exchange of uridine. 4. The facilitated transport of galactose was only slightly inhibited by hexanol. 5. Hexanol was without effect on the passive and active fluxes of Na+ and K+ in red cells with altered cation contents. Cells that were slightly depleted of K+ and cells that were highly K+ -depleted were both insensitive to hexanol.