Stoichiometry and dissociation constants for interaction of tetracaine with mitochondrial adenosinetriphosphatase as determined by fluorescence

The tertiary amine local anesthetic dibucaine binds to the membrane skeletal protein spectrin

The quinoline-based tertiary amine dibucaine has been shown to bind the membrane skeletal protein spectrin with a dissociation constant of 3.5x10(-5) M at 25 degrees C. Such binding is detected by monitoring the quenching of the tryptophan fluorescence intensity with increasing concentrations of dibucaine only and not with the benzene-based local anesthetics procaine, tetracaine and lidocaine. Binding of dibucaine also indicated changes in the tertiary structure of spectrin indicated by a circular dichroism spectrum in the near-UV region due to absorption of the aromatic side chains. The thermodynamic parameters associated with the binding indicated the interaction of dibucaine and spectrin to be enthalpy-driven and insensitive to an increase in the ionic strength of the buffer.

Structural effects of the local anesthetic bupivacaine hydrochloride on the human erythrocyte membrane and molecular models

The interaction of the local anesthetic bupivacaine with the human erythrocyte membrane and molecular models is described. The latter consisted of isolated unsealed human erythrocyte membranes (IUM), large unilamellar vesicles (LUV) of dimyristoylphosphatidylcholine (DMPC), and phospholipid multilayers built-up of DMPC and dimyristoylphosphatidylethanolamine (DMPE), representatives of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. Optical and scanning electron microscopy revealed that bupivacaine induced erythrocyte spheroechinocytosis. According to the bilayer couple hypothesis, this result implied that bupivacaine inserted in the outer monolayer of the erythrocyte membrane. Experiments performed on IUM and DMPC LUV by fluorescence spectroscopy and X-ray diffraction on DMPC and DMPE multilayers confirmed this result. Changes in the molecular organization of membranes alter lipid-protein interactions and induce functional perturbation of membrane proteins such as Na(+) channels. Since local anesthetics may control the influx of Na(+) into the human erythrocyte, in order to relate the structural perturbations induced by bupivacaine in these systems to Na(+) transport, the interaction of this anesthetic with isolated toad skin was also studied. Electrophysiological measurements indicated a significant decrease in the potential difference and in the short-circuit current of the skin after the application of the anesthetic, reflecting inhibition of the active transport of ions. These results suggest that bupivacaine-induced conformational changes of the lipid molecules alter the lipid-protein boundaries of the outer moiety of the erythrocyte membrane, thus interfering with the function of neighboring sodium channels.

Light-induced reversible local fusions of thylakoid membranes in the presence of dibucaine or tetracaine

The dynamics of structural changes in pea chloroplasts in the presence of 25-50 microM dibucaine or tetracaine has been examined using electron microscopy. The light-induced uptake of anesthetic cations by thylakoids is attended by the appearance of local fusions of stroma-exposed thylakoid membranes. The first membrane protrusions and interthylakoid contacts are observed after 4 s illumination and they become numerous by 10 s. As a result, a network of anastomoses is formed which is maintained during at least 10 min. These effects are reversible in the dark and can be reproduced several times. The formation of membrane fusions is inhibited by the addition of protonophore. It is supposed that the energy-dependent uptake of protonated anesthetics by thylakoids leads to an increase in positive surface charge and thus a lateral pressure on the inner side of the thylakoid membrane. The appearance of membrane protrusions (crinkles) having the positive curvature of their inner surface may be considered as a way of compensating for lateral pressure. Presumably, anastomoses result from the fusion of crinkles to adjacent thylakoids.

Inhibition by trifluoperazine of ATP synthesis and hydrolysis by particulate and soluble mitochondrial F1: competition with H2PO4-

The effect of trifluoperazine (TFP) on the ATPase activity of soluble and particulate F1-ATPase and on ATP synthesis driven by succinate oxidation in submitochondrial particles from bovine heart was studied at pH 7.4 and 8.8. At the two pH, TFP inhibited ATP hydrolysis. Inorganic phosphate protected against the inhibiting action of TFP. The results on the effect of various concentrations of phosphate in the reversal of the action of TFP on hydrolysis at pH 7.4 and 8.8 showed that H2PO4- is the species that competes with TFP. The effect of TFP on oxidative phosphorylation was studied at concentrations that do not produce uncoupling or affect the aerobic oxidation of succinate (< 15 microM). TFP inhibited oxidative phosphorylation to a higher extent at pH 8.8 than at pH 7.4; this was through a diminution in the Vmax, and an increase in the Km for phosphate. Data on phosphate uptake during oxidative phosphorylation at several pH showed that H2PO4- is the true substrate for oxidative phosphorylation. Thus, in both synthesis and hydrolysis of ATP, TFP and H2PO4- interact with a common site. However, there is a difference in the sensitivity to TFP of ATP synthesis and hydrolysis; this is more noticeable at pH 8.8, i.e., ATPase activity of soluble F1 remains at about 40% of the activity of the control in a concentration range of TFP of 40-100 microM, whereas in oxidative phosphorylation 14 microM TFP produces a 60% inhibition of phosphate uptake.

Inhibition of cytochrome oxidase by dibucaine

Dibucaine-HCl inhibited mitochondrial cytochrome c oxidase activity in intact mitochondria with 50% inhibition occurring at 1.1 mM dibucaine-HCl. Dibucaine-HCl did not prevent the reduction of cytochrome oxidase by ascorbate plus N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride (TMPD) when measured at 604 nm but prevented 50% of the absorbance change at 445 nm; dithionite reduced the oxidase completely. Dibucaine prevented binding of CO to oxidase reduced with ascorbate plus TMPD by preventing the reduction of cytochrome a3. The midpotenials of cytochrome c and cytochrome oxidase, the visible absorbance wavelength maxima, and the position and intensity of the signals of the EPR spectrum of the oxidase were not affected. Dibucaine-HCl prevented ascorbate plus TMPD-driven reduction of the near infra-red detectable copper center associated with cytochrome a: dithionite subsequently reduced this center. Dibucaine-HCl inhibited cytochrome oxidase activity by interacting between cytochrome a and its associated copper. Since respiration was 8-fold less sensitive in submitochondrial particles, this site of inhibition is on the cytoplasmic side of the membrane.

Mechanism of local anesthetic effect on mitochondrial ATP synthase as deduced from photolabelling and inhibition studies with phenothiazine derivatives

The mode of interaction between mitochondrial ATP synthase and two phenothiazine derivatives, chlorpromazine (CPZ) and trifluoperazine (TFP), was studied as a model for the interaction of local anesthetic drugs with membrane proteins. Photolabelling experiments demonstrated that CPZ and TFP interact with various subunits of either the peripheral F1 moiety of the membrane-embedded F0 sector. Both drugs, however, labelled the membrane sector much more heavily. Qualitative differences in labelling were observed between CPZ and TFP, indicating non-identical sites of interaction. These diversities appeared related to the different hydrophobicities of the two drugs since: (a) TFP, which has a higher lipid/water partition coefficient, labelled the more hydrophobic subunits more markedly than CPZ; (b) reduced glutathione, a hydrophilic free radical scavenger that does not penetrate the membrane continuum, had a negligible effect on the labelling by TFP, whereas it reduced the labelling of various subunits by CPZ; (c) the labelling by [3H]TFP was poorly antagonized by cold CPZ, whereas it was almost totally prevented by fluphenazine, a phenothiazine similar to TFP in hydrophobic character. Consistently, double-inhibition experiments showed that TFP and fluphenazine are mutually exclusive inhibitors of mitochondrial ATP synthase, whereas TFP and CPZ are mutually nonexclusive. The nature of the phospholipid bilayer influenced neither the labelling nor the inhibition patterns. The complex of these data indicate that tertiary amine local anesthetics affect the activity of membrane proteins by interacting with a multiplicity of relatively aspecific hydrophobic sites located preferentially, but not exclusively, on the membrane-embedded domains. It is suggested that at least two phenothiazine derivatives of different hydrophobicities be used in photolabelling experiments, before any generalization is made, since the molecular targets of these drugs vary according to their hydrophobic character.

Photophysical studies of local anesthetics, tetracaine and procaine: drug aggregations

The effects of solvent and concentration on the photophysical properties of tertiary amine local anesthetics, tetracaine and procaine were studied experimentally using low temperature (77 K) emission spectroscopy and confirmed theoretically using a HAM/3 method. For tetracaine free base in methylcyclohexane, a broad fluorescence band observed at approximately 375 nm for concentrations greater than 1 x 10(-3) M is assigned to the molecular self-associated species. The disappearance of this band in ethanol (i.e. a model hydrophobic environment) indicates a greater tendency of neutral tetracaine towards molecular hetero-association. In an aqueous solution of procaine.HCl, a broad emission band centered at approximately 400 nm is detected even at a concentration as low as 1 x 10(-4) M and is attributed to the charged aggregates of procaine.HCl. Two general observations for procaine, tetracaine and dibucaine are noted: (1) the monocation and free base local anesthetics in ethanol solutions give identical photophysical properties, suggesting that the monocation drug species in ethanol is H+ dissociative, and (2) the lowest singlet excited state of neutral local anesthetics is calculated to have a charge-transfer character originating from a non-bonding electron in the N of tertiary amine group to the pi orbital of aromatic ring. The possible pharmacological implications of the deprotonation, the drug aggregations and the charge-transfer excitations of local anesthetics on the molecular basis of anesthesia are discussed.

Mechanism of local anesthetic effect. Involvement of F0 in the inhibition of mitochondrial ATP synthase by phenothiazines

The mechanism whereby tertiary amine local anesthetics affect the activity of membrane proteins was investigated by studying the interaction of phenothiazines with mitochondrial ATP synthase. These drugs caused inhibition of the activity of the membrane-bound enzyme at concentrations that do not perturb the phospholipid bilayer. The inhibitory effect appeared consequent to interaction with multiple sites located on both the F1 and the F0 components of the enzyme complex, since: (a) Dixon plots were parabolic; (b) the membrane-bound enzyme was more sensitive to the drug effect than the isolated F1 component; (c) conditions that decreased oligomycin sensitivity also decreased the sensitivity to phenothiazines; (d) irreversible binding of photochemically activated phenothiazines to the ATP synthase complex, followed by detachment of the F1 moiety and reconstitution with purified F1 resulted in an inhibited enzyme complex. These data are interpreted as indicating that tertiary amine local anesthetics affect the activity of membrane proteins by interacting with hydrophobic sites located on both their integral and peripheral domains.

Inhibition of the bovine-heart mitochondrial F1-ATPase by cationic dyes and amphipathic peptides

The bovine heart mitochondrial F1-ATPase is inhibited by a number of amphiphilic cations. The order of effectiveness of non-peptidyl inhibitors examined as assessed by the concentration estimated to produce 50% inhibition (I0.5) of the enzyme at pH 8.0 is: dequalinium (8 microM), rhodamine 6G (10 microM), malachite green (14 microM), rosaniline (15 microM) greater than acridine orange (180 microM) greater than rhodamine 123 (270 microM) greater than rhodamine B (475 microM), coriphosphine (480 microM) greater than safranin O (1140 microM) greater than pyronin Y (1650 microM) greater than Nile blue A (greater than 2000 microM). The ATPase activity was also inhibited by the following cationic, amphiphilic peptides: the bee venom peptide, melittin; a synthetic peptide corresponding to the presence of yeast cytochrome oxidase subunit IV (WT), and amphiphilic, synthetic peptides which have been shown (Roise, D., Franziska, T., Horvath, S.J., Tomich, J.M., Richards, J.H., Allison, D.S. and Schatz, G. (1988) EMBO J. 7, 649-653) to function in mitochondrial import when attached to dihydrofolate reductase (delta 11.12, Syn-A2, and Syn-C). The order of effectiveness of the peptide inhibitors as assessed by I0.5 values is: Syn-A2 (40 nM), Syn-C (54 nM) greater than melittin (5 microM) greater than WT (16 microM) greater than delta 11,12 (29 microM). Rhodamines B and 123, dequalinium, melittin, and Syn-A2 showed noncompetitive inhibition, whereas each of the other inhibitors examined (rhodamine 6G, rosaniline, malachite green, coriphosphine, acridine orange, and-Syn-C) showed mixed inhibition. Replots of slopes and intercepts from Lineweaver-Burk plots obtained for dequalinium were hyperbolic indicating partial inhibition. With the exception of Syn-C, for which the slope replot was hyperbolic and the intercept replot was parabolic, steady-state kinetic analyses indicated that inhibition by the other inhibitors was complete. The inhibition constants obtained by steady-state kinetic analyses were in agreement with the I0.5 values estimated for each inhibitor examined. Rhodamine 6G, rosaniline, dequalinium, melittin, Syn-A2, and Syn-C were observed to protect F1 against inactivation by the aziridinium of quinacrine mustard in accord with their experimentally determined I0.5 values.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of dibucaine.HCl local anesthetics with bacteriorhodopsin in purple membrane: a spectroscopic study

Several spectroscopic techniques (absorption, emission, transient absorption and differential scanning calorimetry--DSC) were used to investigate the deprotonation of dibucaine.HCl in a hydrophobic environment, and the interaction sites and mechanisms of the local anesthetic dibucaine.HCl on bacteriorhodopsin (bR) in purple membrane. The important results are summarized as follows: (1) the visible absorption features of native (lambda max = 568 nm) and deionized (lambda max = 608 nm) bR are sensitive to the amount of dibucaine.HCl added; (2) the emission spectrum of dibucaine.HCl embedded in the retinal-free mutant bR is similar to that of dibucaine free base in Triton X-100 micellar solutions; (3) the phosphorescence emission of dibucaine at 77 K is completely quenched by bR and the fluorescence quenching rate for the incorporated dibucaine.HCl in bR was determined as kq = 4.09 x 10(13) M-1 s-1; (4) the incorporation of dibucaine.HCl in bR inhibits the slow component rate of formation of M412 and decreases the amount of M412 formation in the photochemical cycle of bR; and (5) the thermal stability of native bR was measured by DSC in the presence and absence of dibucaine and yielded an endothermic transition at 95.9 +/- 1.0 degrees C with 13.6 J/g (3.25 +/- 0.12 cal/g) of enthalpy changes. All observations suggest that the action site of the local anesthetic, dibucaine.HCl, is near or at the chromophore, i.e. the retinal Schiff base of bR. The anesthetic action on bR purple membrane is probably via a specific site binding, but not a conformational mechanism.

Interaction of amphiphiles with integral membrane proteins. II. A simple, minimal model for the nonspecific interaction of amphiphiles with the anion exchanger of the erythrocyte membrane

In a previous paper we have reported on the structural perturbation of the erythrocyte membrane anion exchanger by a regular series of model amphiphiles, as shown by differential scanning calorimetry (Gruber, H.J. and Low, P.S., Biochim. Biophys. Acta, preceding article). Now the data are interpreted by a model in which the effects of amphiphile structure upon buffer-membrane partitioning are well separated from the dependence of the intrinsic potencies of membrane-bound amphiphiles upon amphiphile structure. The buffer-membrane partitioning situation was demonstrated to regularly change between extremes within a series of homologous amphiphiles, i.e. from a negligible to a predominant fraction of total amphiphile in the sample residing in the membrane. Based upon this demonstration a large number of reports on the chain length dependence of apparent potency could be reinterpreted in terms of chain length profiles of intrinsic potency, allowing for a comparison of the responses of various membrane proteins to homologous series of amphiphiles. The response patterns for chain length variation could be divided into three distinct classes: the intrinsic potency (i) can be independent of chain length over a very wide range of length, (ii) it can be rather independent up to a critical length where a sudden cut-off in potency occurs, or (iii) it can drop monotonically over a wide range of chain length. The intrinsic potency values of saturated fatty acids in destabilizing the anion exchanger were interpreted by very simple assumptions: only direct interactions between amphiphiles and target proteins and a simple amphiphile partition equilibrium between a pool of equivalent low affinity sites on the protein and the bulk lipid matrix. The observed monotonic decay of the intrinsic potency of saturated fatty acids with increasing chain length from C8 to C20 was translated into a constant increment of free energy by which each additional CH2 favors the transfer away from sites on the protein towards the bulk lipid matrix. Arguments were presented suggesting that the direct interaction between amphiphiles and target protein is completely nonspecific for alkyl chain length while the residual specificity for shorter over longer amphiphiles is due to the higher tendency of longer chains to preferentially bind in the bulk lipid matrix. Thus a completely new role of the lipid as a competitor, rather than a mediator, was postulated.

The effect of complex formation upon the reduction rates of cytochrome c and cytochrome c peroxidase compound II

The effect of complex formation between ferricytochrome c and cytochrome c peroxidase (Ferrocytochrome-c:hydrogen peroxide oxidoreductase, EC 1.11.1.5) on the reduction of cytochrome c by N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), reduced N-methylphenazonium methosulfate (PMSH), and ascorbate has been determined at low ionic strength (pH 7) and 25 degrees C. Complex formation with the peroxidase enhances the rate of ferricytochrome c reduction by the neutral reductants TMPD and PMSH. Under all experimental conditions investigated, complex formation with cytochrome c peroxidase inhibits the ascorbate reduction of ferricytochrome c. This inhibition is due to the unfavorable electrostatic interactions between the ascorbate dianion and the negatively charged cytochrome c-cytochrome c peroxidase complex. Corrections for the electrostatic term by extrapolating the data to infinite ionic strength suggest that ascorbate can reduce cytochrome c peroxidase-bound cytochrome c faster than free cytochrome c. Reduction of cytochrome c peroxidase Compound II by dicyanobis(1,10-phenanthroline)iron(II) (Fe(phen)2(CN)2) is essentially unaffected by complex formation between the enzyme and ferricytochrome c at low ionic strength (pH 6) and 25 degrees C. However, reduction of Compound II by the negatively changed tetracyano-(1,10-phenanthroline)iron(II) (Fe(phen)(CN)4) is enhanced in the presence of ferricytochrome c. This enhancement is due to the more favorable electrostatic interactions between the reductant and cytochrome c-cytochrome c peroxidase Compound II complex then for Compound II itself. These studies indicate that complex formation between cytochrome c and cytochrome c peroxidase does not sterically block the electron-transfer pathways from these small nonphysiological reductants to the hemes in these two proteins.