Further studies on F1-ATPase inhibition by local anesthetics

An overview of ATP synthase, inhibitors, and their toxicity

Mitochondrial complex V (ATP synthase) is a remarkable molecular motor crucial in generating ATP and sustaining mitochondrial function. Its importance in cellular metabolism cannot be overstated, as malfunction of ATP synthase has been linked to various pathological conditions. Both natural and synthetic ATP synthase inhibitors have been extensively studied, revealing their inhibitory sites and modes of action. These findings have opened exciting avenues for developing new therapeutics and discovering new pesticides and herbicides to safeguard global food supplies. However, it is essential to remember that these compounds can also adversely affect human and animal health, impacting vital organs such as the nervous system, heart, and kidneys. This review aims to provide a comprehensive overview of mitochondrial ATP synthase, its structural and functional features, and the most common inhibitors and their potential toxicities.

Pleiotropic actions of phenothiazine drugs are detrimental to Gram-negative bacterial persister cells

Bacterial persister cells are temporarily tolerant to bactericidal antibiotics but are not necessarily dormant and may exhibit physiological activities leading to cell damage. Based on the link between fluoroquinolone-mediated SOS responses and persister cell recovery, we screened chemicals that target fluoroquinolone persisters. Metabolic inhibitors (e.g., phenothiazines) combined with ofloxacin (OFX) perturbed persister levels in metabolically active cell populations. When metabolically stimulated, intrinsically tolerant stationary phase cells also became OFX-sensitive in the presence of phenothiazines. The effects of phenothiazines on cell metabolism and physiology are highly pleiotropic: at sublethal concentrations, phenothiazines reduce cellular metabolic, transcriptional, and translational activities; impair cell repair and recovery mechanisms; transiently perturb membrane integrity; and disrupt proton motive force by dissipating the proton concentration gradient across the cell membrane. Screening a subset of mutant strains lacking membrane-bound proteins revealed the pleiotropic effects of phenothiazines potentially rely on their ability to inhibit a wide range of critical metabolic proteins. Altogether, our study further highlights the complex roles of metabolism in persister cell formation, survival and recovery, and suggests metabolic inhibitors such as phenothiazines can be selectively detrimental to persister cells.

High-Throughput Screening of a Promoter Library Reveals New Persister Mechanisms in Escherichia Coli

Persister cells are a small subpopulation of phenotypic variants that survive high concentrations of bactericidal antibiotics. Their survival mechanisms are not heritable and can be formed stochastically or triggered by environmental stresses such as antibiotic treatment. In this study, high-throughput screening of an Escherichia coli promoter library and subsequent validation experiments identified several genes whose expression was upregulated by antibiotic treatment. Among the identified genes, waaG, guaA, and guaB were found to be important in persister cell formation in E. coli as their deletion significantly enhanced the sensitivity of cells to various antibiotics. The GuaA and GuaB enzymes form the upstream reactions of ppGpp (a global persister molecule) biosynthesis, and the deletion of guaA and guaB drastically perturbs the ppGpp regulon in E. coli. WaaG, a lipopolysaccharide glucosyltransferase, plays an important role in shaping the outer membrane structure, and the deletion of waaG dissipates the proton gradient (ΔpH) component of cellular proton motive force (PMF), perturbs cellular ATP production, and reduces type I persister formation in stationary phase. Active respiration in the stationary phase, which drives the PMF, was previously shown to play a critical role in type I persister formation, and our results associated with the waaG deficient strain further corroborate these findings. IMPORTANCE Persistence is a nonheritable trait by which normal growing cells switch phenotypically to antibiotic tolerant persister cells. This transient state enables persister cells to recover and grow into an antibiotic-sensitive population. Persister cells have been observed in many pathogenic and nonpathogenic bacteria. Previous studies highlight the complexity and diversity of bacterial persister-cell mechanisms, many of which still remain to be elucidated. Here, using promoter and knockout cell libraries in Escherichia coli, we have identified genes that reveal novel persister mechanisms. As persistence is a critical survival strategy that evolved in many bacteria, our study will enhance the current molecular-level understanding of this conserved mechanism.

Identifying Metabolic Inhibitors to Reduce Bacterial Persistence

Bacterial persisters are rare phenotypic variants that are temporarily tolerant to high concentrations of antibiotics. We have previously discovered that stationary-phase-cell subpopulations exhibiting high redox activities were less capable of producing proteins and resuming growth upon their dilution into fresh media. The redox activities of these cells were maintained by endogenous protein and RNA degradation, resulting in self-inflicted damage that transiently repressed the cellular functions targeted by antibiotics. Here, we showed that pretreatment of stationary-phase cells with an ATP synthase inhibitor, chlorpromazine hydrochloride (CPZ), significantly reduced stationary-phase-redox activities and protein degradation, and yielded cells that were more susceptible to cell death when exposed to antibiotics in fresh media. Leveraging this knowledge, we developed an assay integrating a degradable fluorescent protein system and a small library, containing FDA-approved drugs and antibiotics, to detect medically relevant drugs that potentially target persister metabolism. We identified a subset of chemical inhibitors, including polymyxin B, poly-L-lysine and phenothiazine anti-psychotic drugs, that were able to reduce the persistence phenotype in Escherichia coli. These chemical inhibitors also reduced Pseudomonas aeruginosa persistence, potentially verifying the existence of similar mechanisms in a medically relevant organism.

Sodium Ferulate Attenuates Lidocaine-Induced Corneal Endothelial Impairment

The introduction of intracameral anaesthesia by injection of lidocaine has become popular in cataract surgery for its inherent potency, rapid onset, tissue penetration, and efficiency. However, intracameral lidocaine causes corneal thickening, opacification, and corneal endothelial cell loss. Herein, we investigated the effects of lidocaine combined with sodium ferulate, an antioxidant with antiapoptotic and anti-inflammatory properties, on lidocaine-induced damage of corneal endothelia with in vitro experiment of morphological changes and cell viability of cultured human corneal endothelial cells and in vivo investigation of corneal endothelial cell density and central corneal thickness of cat eyes. Our finding indicates that sodium ferulate from 25 to 200 mg/L significantly reduced 2 g/L lidocaine-induced toxicity to human corneal endothelial cells, and 50 mg/L sodium ferulate recovered the damaged human corneal endothelial cells to normal growth status. Furthermore, 100 mg/L sodium ferulate significantly inhibited lidocaine-induced corneal endothelial cell loss and corneal thickening in cat eyes. In conclusion, sodium ferulate protects human corneal endothelial cells from lidocaine-induced cytotoxicity and attenuates corneal endothelial cell loss and central corneal thickening of cat eyes after intracameral injection with lidocaine. It is likely that the antioxidant effect of sodium ferulate reduces the cytotoxic and inflammatory corneal reaction during intracameral anaesthesia.

ATP synthase and the actions of inhibitors utilized to study its roles in human health, disease, and other scientific areas

ATP synthase, a double-motor enzyme, plays various roles in the cell, participating not only in ATP synthesis but in ATP hydrolysis-dependent processes and in the regulation of a proton gradient across some membrane-dependent systems. Recent studies of ATP synthase as a potential molecular target for the treatment of some human diseases have displayed promising results, and this enzyme is now emerging as an attractive molecular target for the development of new therapies for a variety of diseases. Significantly, ATP synthase, because of its complex structure, is inhibited by a number of different inhibitors and provides diverse possibilities in the development of new ATP synthase-directed agents. In this review, we classify over 250 natural and synthetic inhibitors of ATP synthase reported to date and present their inhibitory sites and their known or proposed modes of action. The rich source of ATP synthase inhibitors and their known or purported sites of action presented in this review should provide valuable insights into their applications as potential scaffolds for new therapeutics for human and animal diseases as well as for the discovery of new pesticides and herbicides to help protect the world's food supply. Finally, as ATP synthase is now known to consist of two unique nanomotors involved in making ATP from ADP and P(i), the information provided in this review may greatly assist those investigators entering the emerging field of nanotechnology.

Drug-induced mitochondrial dysfunction in cardiac and skeletal muscle injury

BACKGROUND

The list of clinically relevant molecules that affect skeletal and cardiac muscle mitochondria is gradually increasing, which strongly suggest that mitochondrial toxicity should be an important end point during the design and testing of novel pharmaceuticals.

OBJECTIVE

The present review intends to describe mechanisms by which clinically relevant drugs are known to alter mitochondrial function in cardiac and skeletal muscle, which is suggested to be involved in the toxicity associated with those drugs.

METHODS

Literature databases were searched in order to identify clinically relevant drugs with associated mitochondrial muscle toxicity.

CONCLUSION

Mitochondrial function is important in the context of muscle survival, hence, the requirement to identify novel mitochondrial targets and develop new therapies to counteract chemical-induced degeneration of mitochondrial function and muscle performance.

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.

Photoinactivation of the F1-ATPase from spinach chloroplasts by dequalinium is accompanied by derivatization of methionine beta183

In contrast to the F1-ATPases from bovine mitochondria and the thermophilic Bacillus PS3, which are reversibly inhibited by dequalinium in the absence of irradiation, the Mg2+-ATPase activity of heat- or dithiothreitol-activated chloroplast F1 (CF1) from spinach chloroplasts is slightly stimulated by dequalinium. Conversely, dequalinium is a partial inhibitor (maximal inhibition is 85-90%) of the Ca2+-ATPase of CF1 activated by heat, dithiothreitol, or octylglucoside. The Mg2+- and Ca2+-ATPase activities of CF1 respond differently in the presence of lauryl dimethylamine oxide (LDAO) in the assay medium. Whereas the Mg2+-ATPase activity of heat- or dithiothreitol-activated CF1 is stimulated up to 14-fold by increasing concentrations of LDAO, the Ca2+-ATPase is inhibited in a biphasic manner by increasing concentrations of LDAO. In the presence of LDAO, dequalinium does not stimulate the heat-activated Mg2+-ATPase over that promoted by LDAO alone. That dequalinium slightly stimulates Mg2+-ATPase activity although it inhibits Ca2+-ATPase activity can be reconciled by assuming that dequalinium binds to two sites in CF1, a stimulatory site that also binds LDAO and an inhibitory site. By acting as a partial inhibitor of the Mg2+-ATPase activity that it activates, the combined effect of dequalinium is modest stimulation. Irradiation of heat- or dithiothreitol-activated CF1 or the alpha3beta3gamma subcomplex of CF1 in the presence of 12 microM dequalinium led to rapid photoinactivation. ATP and ADP, separately or in combination with Mg2+, protect against photoinactivation. After photoinactivating the alpha3beta3gamma subcomplex of CF1 with [14C]dequalinium, tryptic and peptic digests of the isolated, derivatized beta subunit were fractionated by high performance liquid chromatography. Sequencing of the isolated, radioactive tryptic and peptic peptides revealed that Metbeta183, which is at or near the catalytic site, is derivatized in a single beta subunit when CF1 is photoinactivated with [14C]dequalinium.

Unisite hydrolysis of [gamma 32 P]ATP by soluble mitochondrial F1-ATPase and its release by excess ADP and ATP. Effect of trifluoperazine

Some of the characteristics of unisite hydrolysis of [gamma 32P]ATP as well as the changes that occur on the transition to multisite catalysis were further studied. It was found that a fraction of [gamma 32P]ATP bound at the catalytic sites of F1 under unisite conditions undergoes both hydrolysis and release induced by medium nucleotides upon addition of millimolar concentrations of ADP or ATP. The fraction of [gamma 32P]ATP that undergoes release is similar to the fraction that undergoes hydrolytic cleavage, indicating that the rates of the release and hydrolytic reactions of bound [gamma 32P]ATP are in the same range. As part of studies on the mechanisms through which trifluoperazine inhibits ATP hydrolysis, its effect on unisite hydrolysis of [gamma 32P]ATP was also studied. Trifluoperazine diminishes the rate of unisite hydrolysis by 30-40%. The inhibition is accompanied by a nearly tenfold increase in the ratio of [gamma 32P]ATP/32Pi bound at the catalytic site and a 50% diminution in the rate of 32Pi release from the enzyme into the media. Trifluoperazine also induces heterogeneity of the three catalytic sites of F1 in the sense that in a fraction of F1 molecules, the high-affinity catalytic site has a turnover rate lower than the other two. Trifluoperazine does not modify the release of previously bound [gamma 32P]ATP induced by medium nucleotides. The latter indicates that hindrances in the release of Pi do not necesarily accompany alterations in the release of ATP even though both species lie in the same site.

Calcium binding to the subunit c of E. coli ATP-synthase and possible functional implications in energy coupling

The 8-kDa subunit c of the E. coli F0 ATP-synthase proton channel was tested for Ca++ binding activity using a 45Ca++ ligand blot assay after transferring the protein from SDS-PAGE gels onto polyvinyl difluoride membranes. The purified subunit c binds 45Ca++ strongly with Ca++ binding properties very similar to those of the 8-kDa CF0 subunit III of choloroplast thylakoid membranes. The N-terminal f-Met carbonyl group seems necessary for Ca++ binding capacity, shown by loss of Ca++ binding following removal of the formyl group by mild acid treatment. The dicyclohexylcarbodiimide-reactive Asp-61 is not involved in the Ca++ binding, shown by Ca++ binding being retained in two E. coli mutants, Asp61-->Asn and Asp61-->Gly. The Ca++ binding is pH dependent in both the E. coli and thylakoid 8-kDa proteins, being absent at pH 5.0 and rising to a maximum near pH 9.0. A treatment predicted to increase the Ca++ binding affinity to its F0 binding site (chlorpromazine photoaffinity attachment) caused an inhibition of ATP formation driven by a base-to-acid pH jump in whole cells. Inhibition was not observed when the Ca++ chelator EGTA was present with the cells during the chlorpromazine photoaffinity treatment. An apparent Ca++ binding constant on the site responsible for the UV plus chlorpromazine effect of near 80-100 nM was obtained using an EGTA-Ca++ buffer system to control free Ca++ concentration during the UV plus chlorpromazine treatment. The data are consistent with the notion that Ca++ bound to the periplasimic side of the E. coli F0 proton channel can block H+ entry into the channel. A similar effect occurs in thylakoid membranes, but the Ca++ binding site is on the lumen side of the thylakoid, where Ca+2 binding can modulate acid-base jump ATP formation. The Ca+2 binding to the F0 and CF0 complexes is consistent with a pH-dependent gating mechanism for control of H+ ion flux across the opening of the H+ channel.

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.

Charge- and pH-dependent binding sites for dibucaine in ionic micelles: a fluorescence study

Binding of micromolar concentrations of the local anesthetic dibucaine to micelles of cationic, zwitterionic and anionic detergents was studied using the fluorescence emission of dibucaine. Difference in quantum yields for charged and neutral dibucaine allowed to obtain shifts of pKa values due to binding. Estimates for the electrostatic potential affecting the tertiary amine of dibucaine were obtained from the pKa shifts. Change of fluorescence emission upon binding allowed to obtain the binding constants of both charged and neutral dibucaine to the micelles. The binding constant for the neutral form is essentially independent of micelle charge and of specific differences in detergent structure. Consistency between the ratio of neutral to cationic dibucaine binding constants and the measured pKa shift was tested. For LPC micelles complete agreement was found. For CTAC, however, the ratio of binding constants does not explain the pKa shift. The discrepancy between the results is used to estimate the errors involved upon neglecting non-coulombic electrostatic interactions of drugs to charged membrane surfaces. Fluorescence quenching with sodium iodide and nitroxide stearic acid derivatives allowed a depth profiling of the drug in the micelles.

The TF1-ATPase and ATPase activities of assembled alpha 3 beta 3 gamma, alpha 3 beta 3 gamma delta, and alpha 3 beta 3 gamma epsilon complexes are stimulated by low and inhibited by high concentrations of rhodamine 6G whereas the dye only inhibits the alpha 3 beta 3, and alpha 3 beta 3 delta complexes

The ATPase activity of the F1-ATPase from the thermophilic bacterium PS3 is stimulated at concentrations of rhodamine 6G up to about 10 microM where 70% stimulation is observed at 36 degrees C. Half maximal stimulation is observed at about 3 microM dye. At rhodamine 6G concentrations greater than 10 microM, ATPase activity declines with 50% inhibition observed at about 75 microM dye. The ATPase activities of the alpha 3 beta 3 gamma and alpha 3 beta 3 gamma delta complexes assembled from isolated subunits of TF1 expressed in E. coli deleted of the unc operon respond to increasing concentrations of rhodamine 6G nearly identically to the response of TF1. In contrast, the ATPase activities of the alpha 3 beta 3 and alpha 3 beta 3 delta complexes are only inhibited by rhodamine 6G with 50% inhibition observed, respectively, at 35 and 75 microM dye at 36 degrees C. The ATPase activity of TF1 is stimulated up to 4-fold by the neutral detergent, LDAO. In the presence of stimulating concentrations of LDAO, the ATPase activity of TF1 is no longer stimulated by rhodamine 6G, but rather, it is inhibited with 50% inhibition observed at about 30 microM dye at 30 degrees C. One interpretation of these results is that binding of rhodamine 6G to a high-affinity site on TF1 stimulates ATPase activity and unmasks a low-affinity, inhibitory site for the dye which is also exposed by LDAO.

Investigation of class I anti-arrhythmic drug actions on guinea-pig cardiac mitochondrial lactate dehydrogenase activity

1. The effects of the Class I anti-arrhythmic drugs quinidine, procainamide, lidocaine, phenytoin and tocainide on mitochondrial lactate dehydrogenase activity were compared in guinea-pig heart preparations. 2. All the tested drugs inhibited the enzyme activity in a concentration-dependent fashion, exhibiting varying profiles in their actions. Lidocaine exhibited inhibitory concentration 20% (IC20) and IC50 values of 0.52 +/- 0.02 mmol/L and 25.6 +/- 0.5 mmol/L, procainamide 6.0 +/- 0.2 mmol/L and 108 +/- 7.2 mmol/L, phenytoin 3.4 +/- 0.06 mumol/L and 0.34 +/- 0.02 mmol/L, quinidine 39.2 +/- 1.2 mumol/L and 9.8 +/- 0.8 mmol/L and tocainide 2.7 +/- 0.3 mmol/L and 44.6 +/- 2.5 mmol/L. 3. According to the IC50 values, this is the order of their inhibitory potencies: phenytoin > quinidine > lidocaine > tocainide > procainamide. This trend is in general agreement with the lipophilicity rank of the drugs. 4. It is concluded, therefore, that inhibition of mitochondrial lactate dehydrogenase is a property shared by most Class I anti-arrhythmic drugs which may depend on their lipophilicity and possibly their membrane stabilizing effects.

Photoinactivation of the bovine heart mitochondrial F1-ATPase by [14C]dequalinium cross-links phenylalanine-403 or phenylalanine-406 of an alpha subunit to a site or sites contained within residues 440-459 of a beta subunit

Synthesis of [14C]dequalinium, 1,1'-(1,10-[1,10-14C]decanediyl)bis[4-amino-2-methylquinolinium ], is described, which photoinactivates the bovine heart mitochondrial F1-ATPase (MF1). Maximal photoinactivation occurs on incorporation of about 1.5 mol of [14C]dequalinium/mol of MF1. Three radioactive species were resolved when photoinactivated enzyme was submitted to polyacrylamide gel electrophoresis at pH 4.0 in the presence of tetradecyltrimethylammonium bromide, which correspond to the alpha and beta subunits and a cross-linked species with an M(r) of 116,000. Fractionation of a tryptic digest of photoinactivated enzyme by high-performance liquid chromatography led to isolation of a radioactive peptide which contains residues 399-420 of a alpha subunit. Two fragments containing equal amounts of radioactivity were obtained on fractionation of an endoproteinase Asp-N digest of the isolated radioactive tryptic peptide by high-performance liquid chromatography. Amino acid sequence analysis showed that both fragments contained residues 399-408 of the alpha subunit, but one was missing Phe-alpha 403 and the other was lacking Phe-alpha 406. Fractionation of a cyanogen bromide digest of photoinactivated enzyme followed by trypsin digestion of partially purified cyanogen bromide fragments and fractionation of the resulting radioactive tryptic fragments yielded several radioactive species comprised of residues 399-420 of the alpha subunit cross-linked to residues 440-459 of the beta subunit and a radioactive fragment containing residues 399-420 of the alpha subunit. Partial sequence analyses of the cross-linked fragments suggest that Phe-alpha 403 and Phe-alpha 406 participate in cross-links, whereas no information was obtained on the site or sites of cross-linking in the beta subunit fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of class I antiarrhythmic drugs on mitochondrial ATPase activity in guinea pig heart preparations

1. The effects of three class I antiarrhythmic drugs quinidine, lidocaine and lorcainide on undamaged myocardial mitochondrial ATPase [ATP: phosphohydrolase, EC 3.6.1.3] activity were evaluated in guinea pig heart preparations. 2. All three drugs inhibited the enzyme activity in a concentration-dependent fashion. 3. Lorcainide was the most potent, exerting inhibitory effects in the range of less than 1.0 nM-2.0 mM, with IC20 and IC50 values of 9.4 +/- 0.6 nM and 87.2 +/- 5.5 microM. However, in the range of approx. 10 nM-10 microM, the enzyme response decreased only slightly with increasing lorcainide concentrations. 4. Quinidine and lidocaine, on the other hand, inhibited the enzyme activity in the range of 1.0 microM-100 mM. 5. The IC20 and IC50 values for quinidine were 0.92 +/- 0.04 mM and 4.8 +/- 0.6 mM and for lidocaine were 115 +/- 6 microM and 2.3 +/- 0.3 mM. 6. The results show that all three drugs inhibit mitochondrial ATPase activity and that lorcainide is the most potent. 7. These inhibitory effects may be related to the lipophilicity and membrane stabilizing activity of this class of antiarrhythmic drugs.

Functional sites in F1-ATPases: location and interactions

This review focuses on the location and interaction of three functional sites in F1-ATPases. These are catalytic sites which are located in beta subunits, noncatalytic nucleotide-binding sites which are located at interfaces of alpha and beta subunits and modulate the hydrolytic activity of the enzyme, and a site that binds inhibitory amphipathic cations which is at an interface of alpha and beta subunits. The latter site may participate in transmission of conformational signals between catalytic sites in F1 and the proton-conducting apparatus of F0 in the intact ATP synthases.

Induction by psychotropic drugs and local anesthetics of DnaK and GroEL proteins in Escherichia coli

We examined effects of psychotropic drugs and local anesthetics on the synthesis of heat shock proteins in Escherichia coli. Chlorpromazine, a phenothiazine derivative, was shown to induce DnaK and GroEL proteins, major heat shock proteins in E. coli. The inductions of these proteins were not observed in an rpoH (= htpR) amber mutant strain, indicating that the heat shock sigma factor sigma 32 was required for their inductions. Northern blot hybridization analysis revealed that chlorpromazine induced increases of messenger RNAs for the DnaK and GroEL proteins. Thus, the induction occurred at the level of transcription. Chlorpromazine also induced non-heat shock proteins with molecular masses of 21 kDa, 20 kDa, and 17 kDa, even in the rpoH mutant strain. Other psychotropic drugs and local anesthetics, namely, dibucaine, lidocaine, imipramine, tetracaine and procaine, also induced DnaK and GroEL proteins and the small molecular weight proteins.

Kinetic characterization of the normal and procaine-perturbed reaction cycles of the sarcoplasmic reticulum calcium pump

We investigated the effect of the local anesthetic procaine on the activity of the calcium pump protein of sarcoplasmic reticulum (SR) vesicles. Procaine slowed down the rate of calcium uptake by SR vesicles without enhancing the vesicles' passive permeability. This slowing of the unidirectional pumping rate was reflected by the inhibition of the maximal rate of the transport-coupled Ca(2+)-ATPase activity. The inhibition was dependent on Mg2+ concentration; at optimal (i.e. low) concentrations of magnesium, half-maximal inhibition occurred with procaine concentrations close to 15-20 mM. Inhibition of ATPase was not mediated by a change in the properties of the bulk lipid phase. Procaine moderately reduced the true affinity of ATPase for ATP, whereas equilibrium binding of calcium to ATPase in the absence of ATP was virtually not modified by procaine. In fast-kinetics studies, we explored the various intermediate steps in the ATPase catalytic cycle, in order to determine which of them were targets for inhibition by procaine. We found that procaine slowed down ATPase dephosphorylation, an effect which is at least partly responsible for the observed inhibition of overall ATPase activity. In contrast, procaine accelerated the calcium-induced transconformation of unphosphorylated ATPase in the absence of ATP, and altered neither the rate of the Ca(2+)-dependent phosphorylation of ATPase, nor the rate of the dissociation of Ca2+ from phosphorylated ATPase towards the SR lumen, a critical step, the rate of which was measured by a novel fast-filtration method. These results are discussed with respect to the possible site(s) of binding of this amphiphile on the ATPase, and in relation to the contribution of individual steps in the catalytic cycle to the rate limitation of unperturbed SR ATPase activity.

Effect of local anaesthetics on mitochondrial membrane potential in living cells

Using the laser dye rhodamine 123, we demonstrated that local anaesthetics can reach mitochondria in cell culture and reversibly decrease, or even collapse, their transmembrane potential. This effect is highly dependent on the lipid-solubility of the local anaesthetic and can be facilitated by the presence of a lipophilic anion.

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.

A comparative study of the effects of procaine, lidocaine, tetracaine and dibucaine on the functions and ultrastructure of isolated rat liver mitochondria

The effects of procaine, lidocaine, tetracaine and dibucaine (10(-5) - 10(-2) M) were tested on isolated rat liver mitochondria by measurements of the respiratory rates and of the membrane potential and by electron microscopy. A general concentration-dependent stimulation of the basal state (respiration before ADP addition) was observed for all local anesthetics studied. Up to the concentration of 10(-3) M, the order of stimulation was: procaine less than lidocaine less than dibucaine less than tetracaine. However, with the exception of dibucaine, which inhibited state-3 respiration (ADP present) in a strictly concentration-dependent manner, the other drugs had a biphasic effect: slight stimulation of state 3 at low and moderate concentrations (less than or equal to 10(-3) M) and inhibition at higher concentrations. Nevertheless, due to a stronger stimulation of the basal state, the acceptor control ratio decreases progressively (uncoupling effect) as the concentration of the drugs increases. The only exception to this observation is procaine in the range of 10(-5) - 10(-4) M, where the stimulation of the two respiration states (although small) is approximately equal and thus the uncoupling effect is absent or negligible. Membrane potential recordings suggested that membrane integrity and phosphorylation capacity were negatively affected at high drug concentrations (greater than 10(-3) M), especially in the case of tetracaine and dibucaine, when 5 x 10(-3) M even produced the collapse of the membrane potential and complete loss of the phosphorylation ability. Electron microscopy confirmed these effects, showing an abundance of either swollen or supercondensed mitochondria, with many membrane ruptures. The action mechanisms of the tertiary amines studied are discussed in terms of interaction of drug with the lipid bilayer and with the membrane proteins. It is concluded that both the inhibitory and the uncoupling effects are dependent, in the first place, on the degree of hydrophobicity of each local anesthetic.

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.

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.

Stage-dependent inhibition of Plasmodium falciparum by potent Ca2+ and calmodulin modulators

The effects of Ca2+ channel blockers, verapamil, nicardipine and diltiazem, and of potent calmodulin (CaM) inhibitors, trifluoperazine (TFP), calmidazolium, W-7 and W-5, on Plasmodium falciparum in culture were examined. Among Ca2+ blockers, nicardipine was the most potent with the 50% inhibitory concentration (IC50) of 4.3 microM at 72 h after culture. Parasites were more sensitive to calmidazolium and W-7 with IC50 of 3.4 and 4.5 microM, respectively, than to TFP and W-5. All Ca2+ blockers and CaM inhibitors suppressed parasite development at later stages. Nicardipine, diltiazem, calmidazolium and W-5 also retarded parasite development at earlier stages and/or subsequent growth following pretreatment. Verapamil, nicardipine, TFP and calmidazolium reduced erythrocyte invasion by merozoites. Fluorescence microscopy with the cationic fluorescent dye rhodamine 123 revealed that nicardipine, TFP and calmidazolium depolarized both the plasma membrane and mitochondrial membrane potentials of the parasite. It is therefore considered that although all Ca2+ and CaM antagonists tested here influence parasite development at later stages, they are multifunctional, having effects not directly associated with Ca2+ channels or CaM.

Interaction of amphiphiles with integral membrane proteins. I. Structural destabilization of the anion transport protein of the erythrocyte membrane by fatty acids, fatty alcohols, and fatty amines

The effect of model amphiphiles on the structural stability of the anion exchange protein (band 3) of the human erythrocyte membrane was studied by differential scanning calorimetry. The concentration of membranes, as well as the concentration, head group, alkyl chain length, degree of unsaturation, and double bond configuration of a variety of alkane derivatives were all varied in a systematic way. The depression of the denaturation temperature of band 3 per unit membrane concentration of the amphiphile was then determined in order to quantitate the potency of each drug. Saturated fatty acids of chain length C8 to C24 displayed a monotonic decrease in potency up to C20, followed by a dramatic diminution in potency at C22 and C24. Unsaturation caused only minor increases in the abilities of fatty acids to perturb the anion exchanger, and surprisingly, there was neither a trend for the number of double bonds nor a significant cis-trans distinction. Arachidonic acid, as an exception, was much more effective than any other amphiphile in destabilizing band 3. Fatty acids were about three times more potent than fatty amines and fatty alcohols; however, the enhanced partitioning of the latter into the membrane compensated at certain membrane/buffer ratios for its reduced intrinsic potency. A quantitative model interpretation of the data is presented in an accompanying paper.

Evidence for electrogenic accumulation of mefloquine by malarial parasites

The uptake of mefloquine and chloroquine by Plasmodium chabaudi-infected mouse erythrocytes was measured in the presence and absence of ionophores and uncoupler in order to distinguish between the pH-dependent and pH-independent absorption of these drugs. Nigericin and CCCP (carbonylcyanide m-chlorophenylhydrazone) were used to relax the proton gradients and electrical potentials across the membranes. It was found that 40-60% of the mefloquine uptake, and 90% of the chloroquine uptake, was pH-dependent, the remainder being due to passive binding to cellular constituents. The distribution ratio of the pH-dependent uptake for mefloquine was about three times greater than for chloroquine. According to the lysosomotropic weak base hypothesis in which the neutral forms of weak bases are assumed to equilibrate across membranes, the mefloquine distribution should be smaller than the chloroquine distribution: since mefloquine is singly charged and chloroquine is doubly charged, the chloroquine distribution ratio should vary as the square of the mefloquine ratio. We interpret the greater uptake ratio of mefloquine to be evidence for the involvement of secondary active transport, with drug uptake being coupled to proton outflow by an antiporter protein. It is proposed that the uptake of mefloquine is electrogenic, with the proton gradient and the electrical potential both contributing to the driving force, but that the proton gradient alone is responsible for the chloroquine uptake.

Inhibition and photoinactivation of the bovine heart mitochondrial F1-ATPase by the cytotoxic agent, dequalinium

The bovine heart mitochondrial F1-ATPase is inhibited in the dark by the amphipathic cation, dequalinium, with a I0.5 of about 12 microM at pH 7.5. When illuminated at 350 nm in the presence of 1.7 microM dequalinium, the F1-ATPase is inactivated with a pseudo-first order rate constant of 7.9 X 10(-3) min-1. The apparent Kd of the dequalinium-enzyme complex was estimated to be about 12.5 microM by examining the rate of inactivation of the ATPase with 1.7-16.7 microM dequalinium. ATP, ADP, Pi, and Mg2+, singly or in combination, protected the ATPase against photoinactivation, with Mg2+ plus Pi being the most effective.

[Molecular mechanism of action of local anesthetics]

The main target of local anaesthetics on nervous tissue is the sodium channel. Molecular biology and electrophysiology have shown different mechanisms of action on this sodium channel, which depend on the chemical structure and electrostatic charge of the local anaesthetic molecule. There are two main types of action, shown up on the isolated axon, a direct one on the sodium channel itself and an alteration in the lipids surrounding the channel. These effects have been shown on the isolated axon and explain the anaesthetic effect by an inhibition of the sodium current. Experimental studies have also shown the effects of local anaesthetics on different organelles within the cell, and so on intracellular metabolism. Mitochondrial energetic metabolism, and therefore ATP synthesis, is reduced by local anaesthetics at several levels. The respiratory enzyme chain is inhibited by small concentrations of local anaesthetic, especially NADH dehydrogenase and ubiquinone succinate dehydrogenase. Moreover, local anaesthetics increase the mitochondrial membrane permeability to protons, thus removing the moving force behind ATPase activity in ATP synthesis; this leads to a drastic fall in available energy. This effect is further increased by a direct inhibition of ATPase and ATP/ADP translocation. Other enzyme systems of other organelles are also disturbed by local anaesthetics, such as the endoplasmic reticular Ca++ ATPase, which is inhibited, so altering the calcium concentration within the cytosol. Local anaesthetics also inhibit lipolysis and glycogenesis. Receptors such as the acetylcholine receptors are blocked by local anaesthetics. The mechanism of action of these drugs on all these protein systems is two-fold: an alteration of protein structure, but also of the lipids surrounding them.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of human serum and rabbit muscle cholinesterase by local anesthetics

The effects of tertiary amine local anesthetics (procaine, mepivacaine, lidocaine, tetracaine, dibucaine, and bupivacaine) and chlorpromazine were investigated for rabbit muscle acetylcholinesterase and human serum cholinesterase. The muscle enzyme was poorly inhibited by local anesthetics containing an amide linkage. The serum cholinesterase was inhibited by all those compounds, their relative potencies being proportional to their octanol/water partition coefficients. The dissociation constants of tetracaine and procaine, ester anesthetics, were 1000-fold and 100-fold, respectively, that which would be expected from their partition coefficient basis respective to the other amide anesthetics. Procaine showed competitive inhibition of serum cholinesterase, whereas for most anesthetics a mixed type of inhibition was observed. Procaine probably binds at the main anionic site, while the other positively charged anesthetics bind to either the catalytic centre or to the peripheral or modulator anionic site, modifying the kinetic behaviour of cholinesterase as has been demonstrated by the appearance of negative cooperativity for binding to the substrate.

Influence of alcohols, temperature, and region on the mobility of lipids in neuronal membrane

Fluorescence recovery after photobleaching was used to examine lipid diffusibility in different regions of Aplysia neurons. Differences in diffusion of 1-acyl-2-(6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4- yl)]aminohexanoyl)phosphatidylcholine (NBD-C6-PC) in the cell body, axon hillock, and axon were not apparent. Lipid diffusibility during temperature variations and exposure to alcohols was also examined by photobleaching techniques. For these studies, all measurements were made on the cell body. Alcohols were found to be selective in their effects upon the diffusibility of lipid probes. Neither ethanol nor butanol affected the diffusibility of NBD-PC. However, at the same concentrations, both of these alcohols caused a significant increase in the diffusion coefficient (D) for rhodamine-phosphatidylethanolamine (Rho-PE). The diffusion coefficient for NBD-PC in the cell body plasma membrane did not increase with warming, between 4 degrees C and 25 degrees C. The fraction of lipid probe free to diffuse (per cent recovery; %R) however, increased as temperature increased, within this range. The nonconventional relationship between temperature and D was even more pronounced for Rho-PE. As temperature increased, D became smaller for this probe, concurrent with an increase in %R. These results suggest that immobile viscous lipid is recruited into a mobile fraction as temperature increases, resulting in the maintenance of constant diffusibility. The effects of temperature on D and %R, and the selective effects of alcohols on lipid diffusibility suggest that the membrane is heterogeneously organized, on a submicroscopic scale, into domains. The implications of this organization for nerve function and responses of nervous systems to temperature and anesthetics are discussed.

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

The stoichiometry and dissociation constants for the interaction of tetracaine with chloroform-released ATPase prepared from beef heart mitochondria were determined from the enhancement of tetracaine fluorescence intensity that occurs upon binding. There is a single class of approximately 60 thermodynamically equivalent binding sites on ATPase for tetracaine; these have a microscopic dissociation constant of 4.9 X 10(-4) M at 25 degrees C under solvent conditions that are similar to those used for enzyme assay. Analysis of enzyme kinetic data according to a partial noncompetitive scheme gave an inhibitor constant for tetracaine of 4.8 X 10(-4) M. The numerical agreement between the dissociation constant and the inhibitor constant shows that the filling of the same class of sites is probably responsible for both the enzyme inhibition and the fluorescence enhancement. The sites are hydrophobic, as evidenced by the blue shift and the magnitude of the fluorescence enhancement that occur upon binding.

Effect of calmodulin inhibitors on viability and mitochondrial potential of Plasmodium falciparum in culture

Calmodulin inhibitors are toxic for a variety of protozoa. Chlorpromazine, calmidazolium, and trifluoperazine inhibited the incorporation of [3H]hypoxanthine and [3H]phenylalanine into Plasmodium falciparum organisms in cultures with 50% inhibitory concentrations varying from 5.1 microM (with calmidazolium) to 48 microM (with chlorpromazine), the former being more sensitive than the latter. However, these concentrations also immediately dissipated rhodamine 123 from the parasite mitochondrion. Similar concentrations inhibit other protozoa, as well as mammalian cells, and the possibility that mitochondrial function rather than that of calmodulin is the target of these drugs should be considered.

The use of [3H]aniline to identify the essential carboxyl group in the bovine mitochondrial F1-ATPase that reacts with 1-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline

The inactivation of the bovine heart mitochondrial F1-ATPase with 1-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline (EEDQ) in the presence of [3H]aniline at pH 7.0 led to the covalent incorporation of 3H into the enzyme. When the ATPase was inactivated by 94% with 0.9 mM EEDQ in the presence of 3.6 mM [3H]aniline in a large-scale experiment in which the protein concentration was 21 mg/ml, 4.2 mol [3H]anilide were formed per mol enzyme, of which 0.35 mol was incorporated per mol of the alpha subunit and 1.0 mol was incorporated per mol of the beta subunit. Examination of a tryptic digest of the isolated alpha subunit revealed that the majority of the 3H was contained in a single tryptic peptide, which, when purified, was shown to contain the [3H]anilide of a glutamic acid residue which corresponds to alpha-Glu-402 of the Escherichia coli F1-ATPase. This residue was labeled to the extent of about 1.0 mol/mol enzyme. Analysis of tryptic peptides purified from the isolated beta subunit showed that 0.8 and 1.5 mol, respectively, of the [3H]anilides of beta-Glu-341 and beta-Glu-199 were formed per mol MF1 during the inactivation of the enzyme at 21 mg/ml. When the ATPase was inactivated by 90% at a protein concentration of 1.7 mg/ml by 0.9 mM EEDQ in the presence of 1.7 mM [3H]aniline, 3.1 mol [3H]anilide were formed per mol enzyme. From the analysis of the radioactive peptides purified from a tryptic digest of the labeled ATPase from this experiment it was estimated that 0.7 mol of the [3H]anilide of alpha-Glu-402, 0.3 mol of the [3H]anilide of beta-Glu-341, and 1.5 mol of the [3H]anilide of beta-Glu-199 were formed per mol F1-ATPase. Since beta-Glu-199 is labeled to the same extent in the two experiments while alpha-Glu-402 and beta-Glu-341 were not, suggests that the modification of beta-Glu-199 is responsible for inactivation of the enzyme by EEDQ.

The effect of Co(III)(NH3)4ATP on the kinetics of beef heart mitochondrial ATPase

Bidentate cobalt(III)tetraamine adenosine triphosphate [Co(NH3)4ATP] was investigated as an inhibitor of the beef heart mitochondrial F1-ATPase. The compound was found to have a mixed noncompetitive mechanism with a Ki of 0.4 mM and an alpha of 1.4 during ATP hydrolysis. Co(NH3)4ATP also noncompetitively inhibited ATP hydrolysis in the presence of bicarbonate. ITP hydrolysis was similarly affected. Co(NH3)4ATP was also used in dual inhibitor studies with adenylylimidodiphosphate (AMP-PNP) and azide; it was found to be mutually exclusive with AMP-PNP and azide. The compound also protected the F1 from modification by 4-chloro-7-nitrobenzofurazan. These results are discussed in terms of the regulation of the ATP hydrolysis reaction.

Reciprocal effects of phenothiazines and naphthalene sulfonamides on the external ATP-dependent permeability change in Chinese hamster ovary cells

External ATP causes a great increase in passive permeability to phosphorylated metabolites in several transformed cells, but not in untransformed cells. We have previously demonstrated that the external ATP-dependent permeability change was induced in Chinese hamster ovary cells, CHO-K1, only in the presence of a mitochondrial inhibitor (rotenone, KCN) or a cytoskeleton-attacking agent, vinblastine (Kitagawa, T. and Akamatsu, Y. Biochim. Biophys. Acta 649, 76-82 (1981); 734, 25-32 (1983]. A similar ATP-dependent permeability change was also induced in CHO cells when the cells were treated with 10-30 microM trifluoperazine. This permeability change, like the previously mentioned ones, was found to be reversible and the treated cells remained viable. The permeability change induced by ATP and trifluoperazine was independent of changes in cellular ATP concentration and this property was the same as that of the permeability change with external ATP and vinblastine. Since trifluoperazine is known to interact with calmodulin and to inhibit calmodulin-dependent cellular functions, these results may indicate that calmodulin associated with the cytoskeleton plays an important role in control of the permeability change, although nonspecific perturbation by the drug of the membranes cannot be ruled out. Chlorpromazine and a naphthalene sulfonamide, W-7, also induced an ATP-dependent permeability change. However, these drugs, like mitochondrial inhibitors, reduced the cellular ATP concentration to induce the permeability change. Thus, a clear difference in the action of these drugs in intact cells was also shown in this study. Possible mechanisms for the ATP-dependent permeability change in mammalian cells are discussed.

The varied responses of different F1-ATPases to chlorpromazine

The effects of chlorpromazine on various properties of the F1-ATPases from bovine heart mitochondria (MF1), the plasma membranes of Escherichia coli (EF1), and plasma membranes of the thermophilic bacterium PS3 (TF1) have been examined. While chlorpromazine inhibited MF1 with an I0.5 of about 50 microM and EF1 with an I0.5 of about 150 microM at 23 degrees C, the ATPase activity of TF1 was stimulated by chlorpromazine concentrations up to 0.6 mM at this temperature. Maximal activation of about 20% was observed at 0.2 mM chlorpromazine at 23 degrees C. Chlorpromazine concentrations greater than 0.6 mM inhibited TF1 at 23 degrees C. At 37 degrees C the ATPase activity of TF1 was doubled in the presence of 0.5 mM chlorpromazine, the concentration at which maximal stimulation was observed at this temperature. Chlorpromazine inhibited the rate of inactivation of EF1 by dicyclohexylcarbodiimide (DCCD) at 23 degrees C and pH 6.5. Concentrations of chlorpromazine which inhibited the ATPase activity of TF1 at pH 7.0 accelerated the rate of inactivation of the enzyme by DCCD at pH 6.5, while lower concentrations of the phenothiazine, which stimulated the ATPase, had no effect on DCCD inactivation. Chlorpromazine concentrations up to 1.0 mM had no effect on the rate of inactivation of TF1 by DCCD at 37 degrees C and pH 6.5. Chlorpromazine at 0.5 mM accelerated the rate of inactivation of MF1 by 5'-p-fluorosulfonylbenzoyladenosine (FSBA), while it slowed the rate of inactivation of EF1 by FSBA. The inactivation of TF1 by FSBA in the absence of chlorpromazine was complex and was not included in this comparison. Chlorpromazine protected MF1 and EF1 against cold inactivation. Whereas 100 microM chlorpromazine afforded about 90% stabilization of MF1 at 4 degrees C, only about 30% stabilization of EF1 was observed under the same conditions in the presence of 400 microM chlorpromazine. Each of the ATPases was inactivated by the structural analog of chlorpromazine, quinacrine mustard. Whereas 5 mM ATP and 5 mM ADP protected MF1 and TF1 against inactivation by 0.5 mM quinacrine mustard, the rate of inactivation of EF1 by quinacrine mustard was accelerated fourfold by 5 mM ATP and slightly accelerated by 5 mM ADP.

Local anesthetics: a new class of partial inhibitors of mitochondrial ATPase

The following characteristics are reported for mitochondrial ATPase prepared by the chloroform extraction method: (1) The pH optimum for enzyme activity is at 8.0. (2) The neutral anesthetic benzocaine inhibits the enzyme at all pH values. (3) Reciprocal plots of 1/v versus 1/[ATP] show that inhibition by lidocaine, tetracaine, dibucaine, and chlorpromazine is noncompetitive; slope and intercept replots are hyperbolic, showing that the inhibition is partial rather than complete.