Inhibition of phospholipase A-induced swelling of mitochondria by local anesthetics and related agents

A historical review of cellular calcium handling, with emphasis on mitochondria

Calcium ions are of central importance in cellular physiology, as they carry the signal activating cells to perform their programmed function. Ca(2+) is particularly suitable for this role because of its chemical properties and because its free concentration gradient between the extra-cellular and the cytosolic concentrations is very high, about four orders of magnitude. The cytosolic concentration of Ca(2+) is regulated by binding and chelation by various substances and by transport across plasma and intracellular membranes. Various channels, transport ATPases, uniporters, and antiporters in the plasma membrane, endoplasmic and sarcoplasmic reticulum, and mitochondria are responsible for the transport of Ca(2+). The regulation of these transport systems is the subject of an increasing number of studies. In this short review, we focus on the mitochondrial transporters, i.e. the calcium uniporter used for Ca(2+) uptake, and the antiporters used for the efflux, i.e. the Ca(2+)/Na(+) antiporter in mitochondria and the plasma membrane of excitable cells, and the Ca(2+)/nH(+) antiporter in liver and some other mitochondrial types. Mitochondria are of special interest in that Ca(2+) stimulates respiration and oxidative phosphorylation to meet the energy needs of activated cells. The studies on Ca(2+) and mitochondria began in the fifties, but interest in mitochondrial Ca(2+) handling faded in the late seventies since it had become apparent that mitochondria in resting cells contain very low Ca(2+). Interest increased again in the nineties also because it was discovered that mitochondria and Ca(2+) had a central role in apoptosis and necrosis. This is of special interest in calcium overload and oxidative stress conditions, when the opening of the mitochondrial permeability transition pore is stimulated.

Interaction of plant lipids with 14 kDa phospholipase A2 enzymes

Several structurally related plant lipids were isolated and their effect was assessed on the enzyme activity of group I (pancreatic and Naja mocambique venom) and group II (Crotalus atrox venom) phospholipase A2 (PLA2) enzymes, with labelled Escherichia coli as an enzyme substrate. The neutral monogalactosyldiacylglycerol (MGDG) and negatively charged diacylglyceryl alpha-D-glucuronide (DGGA) did not influence the enzyme activity of either group. Digalactosyldiacylglycerol (DGDG), another uncharged glycolipid, inhibited PLA2 activity in a dose-dependent manner to 60-70% of the control. Sulphoquinovosyldiacylglycerol (SQDG), which is also anionic, activated both groups of PLA2 enzyme. A similar activation was observed with the zwitterionic diacylglyceryl-O-(N,N,N-trimethylhomoserine) (DGTS) and diacylglyceryl-O-(hydroxymethyl)(N,N, N-trimethyl)-beta-alanine (DGTA). DGDG, SQDG and DGTS are dispersed homogeneously with low critical micelle concentrations (CMCs). The hydrodynamic radius of neutral DGDG is an order of magnitude larger than the charged lipids SQDG and DGTS. The inhibition of pig pancreatic PLA2 by DGDG was dependent on substrate concentration. The intrinsic fluorescence spectra of the enzyme was not changed in the presence of native or hydrogenated DGDG. Thus the inhibition is most probably due to a non-specific interaction of plant lipids with the substrate. Different lengths and saturations of the fatty acyl chains of DGDG did not alter the inhibition of PLA2, whereas deacylation abrogated the inhibitory effect. Both SQDG and DGTS activated pig pancreatic PLA2 in a dose-dependent manner. Saturation of the double bonds of these lipids decreased the activating effect. The fluorescence of pig pancreatic PLA2 incubated with SQDG and DGTS was enhanced by 2-fold and 3-fold respectively, suggesting the formation of a complex between enzyme and lipids. In conclusion, the effect of different plant lipids on PLA2 activity depends on different structural elements of the polar head group and their charge as well as the degree of unsaturation of the fatty acyl chains.

The significant role of membrane stabilization in hypothermic cardioplegic cardiac preservation in a canine experimental model

Isolated mongrel hearts were preserved for 6 h at 5 degrees C followed by normothermic reperfusion for 2 h. The dogs were divided into three groups; K+-cardioplegic solution alone, group C, n = 7; K+-cardioplegic solution with lidocaine 200 mg/l, group L, n = 7; and K+-cardioplegic solution with betamethasone 250 mg/l and lidocaine 200 mg/l, group B + L, n = 7. Ventricular fibrillation occurred early during reperfusion in all dogs in group C, in one of seven in group L, and in two of seven dogs in group B + L. The serum MB fraction of creatinine kinase (MB-CK), mitochondrial aspartate aminotransferase (m-AAT) and calcium overload were suppressed to a greater extent in both groups L and B + L during reperfusion compared to group C. Myocardial ATP, total adenine nucleotide, and creatine phosphate did not differ between the three groups at the end of reperfusion. Myocardial ADP and AMP declined significantly during reperfusion in group C, however, they remained unchanged in group B + L and increased in group L which showed significantly higher levels compared to group C. Left ventricular functional recovery during reperfusion was consistently better in both group L and B + L compared to group C. These results suggested that membrane stabilization prevents myocardial damage from hypothermia and cardioplegia and provides better myocardial viability and functional recovery in donor heart preservation.

Myocardial preservation using lidocaine blood cardioplegia

Prevention of ventricular fibrillation after aortic unclamping using lidocaine hydrochloride as an additive to cold potassium blood cardioplegia was studied prospectively in 46 patients undergoing elective myocardial revascularization. Patients were similar with respect to age, ventricular function, severity of coronary artery disease, cross-clamp time, completeness of revascularization, frequency of internal thoracic artery grafting, systemic temperature at the time of cross-clamp removal, and mean infusate volume and temperature. Patients receiving lidocaine blood cardioplegia (group 1, 23 patients) had a significant reduction in the incidence of ventricular fibrillation (22% versus 74%; p less than 0.0005) and in the mean number of cardioversion attempts required to defibrillate the heart (0.5 +/- 1.3 versus 1.9 +/- 0.97; p less than 0.0005) after cross-clamp removal compared with controls (group 2, 23 patients). There were no differences between the two groups postoperatively with regard to cardiac enzyme release, hemodynamic measurements, or clinical outcome. Patients receiving lidocaine blood cardioplegia tended to have a lower incidence of new postoperative atrial fibrillation (9% versus 26%). Ventricular function was preserved equally in both groups. We conclude that lidocaine is a safe additive to potassium blood cardioplegia and significantly reduces the incidence of ventricular fibrillation after aortic unclamping.

Skeletal muscle mitochondrial respiration of malignant hyperthermia-susceptible patients. Ca2+-induced uncoupling and free fatty acids

1. Skeletal muscle mitochondria of malignant hyperthermia (MH)-susceptible patients showed normal oxidative phosphorylation but were more easily uncoupled than normal by exogenous Ca2+. 2. Fatty acids, in stimulating the mitochondrial ATPase activity, are responsible for the enhanced State 4 respiration in MH-susceptible patients. 3. These results imply that skeletal muscle mitochondria and free fatty acids are associated with the development of MH syndrome.

Influence of beta-adrenoceptor blocking drugs on lipid-protein interaction in synaptosomal membranes. An ESR study

The influence of the beta-adrenoceptor blocking drugs atenolol, doberol, propranolol and exaprolol on synaptosomal membranes was studied using ESR spectroscopy of stearic acid spin labeled at the 16th position. The drugs changed the ESR spectra of the label in the membranes, where in addition to changes of a fluid lipid component they increased the proportion of a motionally-restricted component. No motionally-restricted component was found in the samples prepared from brain total lipid liposomes treated with the drugs. The drug propensities at 20 mmol/l concentration to increase the proportion of the motionally-restricted component in the following order, control less than doberol approximately atenolol less than or equal to propranolol less than exaprolol did not correlate with their potency to influence the dynamics of the bulk lipid membrane phase. The motionally-restricted component induced by exaprolol increased with raising temperature and prolongation of time of the sample incubation. The results indicate that the beta-adrenoceptor blocking drugs influence lipid-protein interaction in the synaptosomal membranes, which could be important for elucidation of their mechanism of biological membrane activities.

Inhibition of human non-pancreatic phospholipases A2 by retinoids and flavonoids. Mechanism of action

The interaction of retinoids and flavonoids with phospholipases A2 (PLA2) was studied to assess the mechanism of inhibition. Retinoids, such as retinal, retinol, retinoic acid and retinol acetate, and flavonoids, such as quercetin, rutin, morin and sciadopitysin, inhibit Ca2+-dependent PLA2 activity of human synovial fluid (HSF) in vitro in a dose-dependent fashion; ID20S ranged from 2-8 microM. Retinal inhibited neutral active Ca2+-dependent PLA2S from human platelets, human plasma, human polymorphonuclear leukocytes and Naja mossambica mossambica venom in a dose-dependent manner while quercetin inhibits extracellular PLA2 activities of human plasma, HSF and N. m. mossambica venom in a dose-dependent manner but not PLA2 activity derived from human platelets and polymorphomonuclear leukocytes. Inhibition of PLA2 activity by both flavonoid and retinoids were independent of Ca2+ or Na+. Increasing substrate concentration (9-144 nmols) relieved the inhibition of HSF-PLA2 activity by quercetin indicating probable interaction with the substrate. The inhibition by retinal is independent of substrate concentration suggesting that inhibition by retinal is probably due to direct interaction with the enzyme. both retinal and quercetin quenched the relative fluorescent intensity of N. m. mossambica PLA2 and in a dose-dependent manner in the same concentration range at which they inhibit in vitro PLA2 activity. Retinal and quercetin shift the thermotropic phase transition of distearoylphosphatidylethanolamine (DSPE) liposomes. Both compounds broadened the transition peak, shifted the Tm to lower temperature, and decreased enthalpy significantly. These findings indicate that inhibition of non-pancreatic human PLA2S by retinoids and flavonoids can be mediated by interaction with enzyme and/or substrate.

Malignant hyperthermia: molecular defects in membrane permeability

Malignant hyperthermia (MH), a genetically inherited disorder of skeletal muscle, is due to molecular defect in membrane permeability. The alteration in membrane permeability is suggested to be due to enhanced phospholipase A2 activity which is responsible for the increased level in sarcoplasmic Ca2+. The excess Ca2+ is responsible for muscle hyper-rigidity and enhanced rate of glycolysis, resulting in a rapid rate of lactic acid production and a low pH in MH muscle.

Cationic amphiphilic drugs inhibit the synthesis of long-chain fatty acyl coenzyme A in rat brain microsomes

The effect of cationic amphiphilic drugs (CAD) on the synthesis of thiol esters of coenzyme A with long-chain fatty acids was studied in microsomes of rat brain in vitro. The results indicate that propranolol, tetracaine and to a lesser extent, chloroquine, inhibit enzyme activity. Procaine and lidocaine did not inhibit enzyme activity in concentrations up to 0.8 mM. This inhibition seems to be directed primarily to the synthesis of polyunsaturated fatty acyl coenzyme A. The results also suggest that this inhibition may be due to the action of CAD on the microsomal membrane and not to an interaction of these drugs with the fatty acid substrates.

Effect of ruthenium red on the Ca2+ and Sr2+ efflux from rat liver mitochondria: influence of nupercaine

The rate of ruthenium-red-induced Ca2+ efflux depends on the time that the calcium interacts with the mitochondria prior to the addition of the inhibitor. This time-dependency is abolished in the presence of nupercaine; it does not occur in the case of Sr2+ efflux from mitochondria in which the endogenous Ca2+ has been substituted by strontium (strontium-treated mitochondria, STM). Ruthenium red inhibits the respiratory-inhibitor- or uncoupler-induced Sr2+ efflux from STM, but not the Ca2+ efflux from standard mitochondria. The influence of the calcium-induced mitochondrial damage upon the effect of ruthenium red is discussed.

Myocardial protection by lidocaine hydrochloride in aorto-coronary bypass surgery

Myocardial protective effect of lidocaine hydrochloride on the ischemic myocardium was evaluated by serum (MB-CK) and cardiac function in 48 patients; 24 patients in control (C) and 24 patients in lidocaine-treated group (L), who underwent aorto-coronary bypass surgery. Lidocaine hydrochloride, 1 mg/min was administered by continuous drip infusion from initiation of anesthesia, and throughout the operation and postoperative period for 24 hours. There were no significant differences between two groups with regard to duration of cardioplegia and cardiopulmonary bypass, hypothermic level and the number of grafts implanted. Serum MB-CK at 18-24 hours following cardioplegia was 39.5 +/- 15.2 I.U. (C) and 14.2 +/- 4.0 I.U. (L), (p less than 0.05). Cardiac index and stroke volume index were significantly increased in the lidocaine-treated group at 24 hours following aorto-coronary bypass surgery, as compared to the control group. Lidocaine thus appears to be beneficial in aorto-coronary bypass surgery to prevent ischemic changes in the myocardium.

Effect of chlorpromazine on isolated rat hepatocytes

The effect of chlorpromazine hydrochloride (CPZ) (1-500 microM) on plasma membrane permeability and mitochondrial respiratory function of isolated rat hepatocytes was studied. The endogenous oxygen consumption stimulated by 1 mM succinate was increased significantly by 5 microM CPZ, whereas the ability to exclude trypan blue (TB) was decreased significantly by 100 microM CPZ. The release of a cytosomal enzyme, lactate dehydrogenase (LDH), was increased significantly by 50 microM CPZ, whereas the release of glutamic-opalacetic transaminase (GOT) was increased significantly by 100 microM. The endogenous oxygen consumption was decreased significantly by 150 microM CPZ. The respiration control ratio by 2 microM carbonylcyanide-m-chlorphenyl hydrazon (CCP) showed significant decreases at all concentrations of CPZ studied; and this might be attributable to the suppression by CPZ of the respiratory stimulation induced by CCP. The results indicated that CPZ at a low concentration (5 microM) first produced a significant change in plasma membrane permeability to low molecular substances such as succinate and then at higher concentrations (50-100 microM) produced significant release of the cytosomal and mitochondrial enzymes, LDH and GOT. They also indicated that the concentrations of CPZ which produced significant effects on respiratory function were higher (above 150 microM) than those which produced significant changes in plasma membrane permeability of hepatocytes.

Mitochondrial calcium transport and calcium-activated phospholipase in porcine malignant hyperthermia

The interaction of Ca2+ with mitochondria isolated from longissismus dorsi, a predominantly white skeletal muscle, of normal and malignant hyperthermia pigs was investigated using tightly-coupled preparations. Arrhenius plots of mitochondrial Ca2+ -stimulated respiration for succinate oxidation of malignant hyperthermia pigs showed a transition temperature (Tt) of 26.31 +/- 0.80 degrees C (n = 5), which was decreased by spermine to 15.41 +/- 0.69 degrees C (n = 3), a value very similar to that for normal pigs. No difference in either the Tt or in the activation energy (Ea) was observed between the two types of pigs when ADP was used instead of Ca2+. Mitochondria of malignant hyperthermia pigs were uncoupled at 40 degrees C by exogenous Ca2+ at 1221 +/- 301 (n = 9) nmol Ca2+ per mg proteinn during succinate oxidation and the uncoupled mitochondria showed large amplitude swelling. Both the Ca2+ -induced uncoupling and swelling were prevented by bovine serum albumin and by the phospholipase inhibitors, spermine and tetracaine. In contrast, mitochondria of normal pigs were still tightly coupled even after a total addition of 2313 +/- 287 (n = 5) nmol Ca2+ per mg protein and retained the original condensed configuration in the presence or absence of spermine and tetracaine. Mitochondria of malignant hyperthermia pigs contained significantly (P less than 0.001) higher quantities of endogenous Ca2+ and showed a significantly (P less than 0.001) faster FCCP-induced endogenous Ca2+ efflux rate than normal when monitored spectroscopically with murexide. No significant difference was observed in either the rate of exogenous Ca2+ uptake or in the extent of Ca2+ accumulated in the aerobic steady state during succinate oxidation between the two types of pigs. The rate of mitochondrial Ca2+ efflux of malignant hyperthermia pigs during anaerobiosis was about twice that of normal. Experimental evidence suggests that mitochondria from musculi longissimus dorsi of malignant hyperthermia pigs contained a Ca2+ -stimulated phospholipase A2 (EC 3.1.1.4, phosphatide 2-acylhydrolase), and that this enzyme if present in mitochondria of normal pigs is either latent or in very low concentration. The significance of the Ca2+ -stimulated phospholipase A2 and its association with the enhanced rate of glycolysis in porcine malignant hyperthermia syndrome and in the post-mortem formation of the pale, soft and exudative conditions observed in white skeletal muscles of malignant hyperthermia pigs is discussed.

The effect of local anesthetics on arterial lipid metabolism. Inhibition of sterol esterification in vitro

The local anesthetics lidocaine, tetracaine, benzocaine and dibucaine were found to inhibit sterol esterification by acylCoA:cholesterol acyltransferase (ACAT, EC 2.3.1.26) in the microsomal fraction isolated from rabbit aortas. In arterial microsomes, the incorporation of [14C]oleoylCoA into [14C]steryl esters was inhibited in a dose-dependent way by the anesthetics over the concentration range 0.25-5.0 mM. The potency of inhibition was dibucaine greater than benzocaine greater than tetracaine greater than lidocaine greater than procaine with inhibition of about 85% occurring with 0.25 mM dibucaine. Sterol esterification to [14C]oleic acid was also inhibited by the anesthetics in intact aortic tissue from the rabbit, dog, and rat. A detailed study of the effects of 5 mM lidocaine on lipid biosynthesis in the rabbit aorta in vitro revealed that lidocaine not only inhibited sterol esterification to [14C]oleate but stimulated [14C]oleate incorporation into glycerides.

Lidocaine-induced reduction in size of experimental myocardial infarction

In anesthetized open chest dogs, the effects of therapeutic doses of lidocaine on myocardial cell respiration, creatine kinase depletion, left ventricular stroke work and cardiac necrosis were assessed. The dogs were subjected to 40 minutes of occlusion of the left anterior descending coronary artery, followed by 5 hours of reperfusion. Group I (12 dogs) had infusion of saline solution; group II (8 dogs) had infusion of 0.2 mg/kg per min of lidocaine (serum level 16.8 +/- 1.4 microgram/ml); group III (5 dogs) had infusion of 0.04 mg/kg per min or lidocaine (serum level 3.6 micrograms/ml). Ischemic regional myocardial blood flow (measured by 9 micrometer spheres of strontium-85) was 6.34 +/- 1.62 ml/100 mg per min in group I, 1.48 +/- 0.59 in group II (p < 0.05) and 1.32 +/- 0.50 in group III (p < 0.05). Oxygen consumed during conversion of adenosine diphosphate to adenosine triphosphate in mitochondria from control and lidocaine-treated ischemic tissue was depressed (p < 0.05) and correlated (r = 0.63) with creatine kinase depletion. Left ventricular stroke work was not significantly different among the three groups. Infarct size (in percent of left ventricular weight) was 12.6 +/- 2.0 for group I, 4.8 +/- 1.2 for group II (p < 0.01) and 4.8 +/- 2.5 for group III (p < 0.05). The data suggest that the reduction of myocardial infarct size by lidocaine was not dependent on enhanced myocardial blood flow and was independent of left ventricular stroke work.

Factors controlling the metabolism of phosphatidate by phosphohydrolase and phospholipase A-type activities. Effects of magnesium, calcium and amphiphilic cationic drugs

1. The simultaneous deacylation and dephosphorylation of 1,2-diacyl-sn-[3H]glycerol 3-phosphate by the microsomal and soluble fraction of rat liver was studied. The substrate was either in the form of an emulsion or bound to microsomal membranes. 2. Mg2+ stimulated the deacylation and dephosphorylation of phosphatidate emulsions by both fractions, although the stimulation of both microsomal activities was less than that in the soluble fraction. The preparations of membrane-bound phosphatidate contained Mg2+. Further addition of Mg2+ inhibited dephosphorylation, whereas low concentrations of EDTA stimulated. Additional Mg2+ had little effect on the deacylation of membrane-bound phosphatidate and EDTA inhibited it. 3. Ca2+ inhibited the phosphohydrolase reactions in both fractions, but had little effect on the deacylation of phosphatidate emulsions or membrane-bound phosphatidate. 4. In the absence of Mg2+, lower concentrations of amphiphilic cations (chlorpromazine and benfluorex) stimulated the deacylation and dephosphorylation of phosphatidate emulsions by the soluble fraction. They also stimulated deacylation by the microsomal fraction, but inhibited dephosphorylation. In the present of 5 mM MgCl2, these drugs inhibited the dephosphorylation and deacylation of phosphatidate emulsions, the deacylation reaction being slightly less sensitive. Chlorpromazine (0.4 and 0.8 mM) also inhibited the dephosphorylation of membrane-bound Mg2+-phosphatidate by microsomal and microsomal plus soluble fractions. The deacylation was stimulated by 0.4 mM chlorpromazine and by 1 and 2 mM norfenfluramine. Chlorpromazine (0.8 mM) inhibited the deacylation by microsomal plus soluble fractions, but not by microsomal fractions alone. 5. The possible importance of the deacylation of phosphatidate in the physiological and pharmacological control of glycerolipid synthesis is discussed.

The action of Nupercaine on calcium efflux from rat liver mitochondria

1. Nupercaine inhibits the Ca2+ efflux from rat liver mitochondria observed in the presence of Ruthenium Red, 50% inhibition being obtained at 80 microM-Nupercaine. 2. Neither the Ruthenium Red-stimulated efflux nor its inhibition by Nupercaine can be directly attributed to effects on mitochondrial stability. 3. Nupercaine perturbs the steady-state external Ca2+ concentration in the absence of Ruthenium Red to an extent that is explicable in terms of the inhibition of Ca2+ efflux. 4. Various factors that are likely to be involved in determining steady-state extra-mitochondrial Ca2+ concentrations are discussed.

Phospholipase A2 inhibitors and their possible clinical use in the treatment of acute pancreatitis

A laboratory method was established for measurement of phospholipase A2 activity in buffer and serum. A series of different phospholipase A2 inhibitors was tested. The most effective inhibitors were Ca2+ chelating compounds like EDTA, DTPA, EGTA, and phytic acid. The calcium salt of EDTA also has some inhibitory effect. Serum phospholipase A2 activity in normal healthy control patients was measured. The activity in 27 patients with acute pancreatitis was tested. The activity was abnormally high in five patients. This activity was in vitro inhibited by EDTA and partly by CaNa2EDTA. The clinical picture of these patients did not differ from that of phospholipase-A2-negative patients. Six patients with acute pancreatitis were treated by intravenous infusion of CaNA2EDTA. Two of them had haemorrhagic pancreatitis and two were suspected of having early haemorrhagic pancreatitis. During the CaNa2EDTA infusion serum amylase and phospholipase A2 activities decreased. All patients recovered. No harmful side effects were noticed.

The effects of amphiphilic compounds on phosphatidate metabolism

Amphiphilic cations interact with phosphatidate and thereby change its physical properties. This interaction can redirect phospholipid metabolism. In the presence of Mg2+ amphiphilic cations inhibit the activity of phosphatidate phosphohydrolase and stimulate that of phosphatidate cytidylyltransferase. Increasing the concentration of Mg2+ further, or adding Ca2+ have similar effects, except that Ca2+ does not stimulate phosphatidate cytidylyltransferase activity. Amphiphilic anions reverse the effects caused by the amphiphilic cations. The implication of these results are discussed in relation to the pharmacological effects of amphiphilic cationic drugs.

Effect of p-bromophenacyl bromide, an inhibitor of phospholipase A2, on arachidonic acid release and prostaglandin synthesis by the guinea-pig uterus in vitro

The synthesis of prostaglandins F2alpha and E2 by guinea-pig uterine homogenates was inhibited by p-bromophenacyl bromide (PBPAB), an inhibitor of phospholipase A2. 2 Metabolism of prostaglandin F2alpha by uterine homogenates was undetectable; this was not affected by PBPAB. 3 There was no significant difference between the amounts of arachidonic acid released from uterine homogenates on days 7 and 1k of the oestrous cycle. Small amounts of dihomo-gamma-linolenic acid were detected in the homogenates. 4 The release of arachidonic acid from uterine homogenates was greatly inhibited by PBPAB. 5 Addition of exogenous arachidonic acid to uterine homogenates did not overcome the inhibition of uterine prostaglandin F2alpha synthesis produced by PBPAB. 6 It is concluded that PBPAB inhibits both the release of arachidonic acid from the guinea-pig uterus and its subsequent conversion into prostaglandins.

Effects of local anaesthetics on phospholipases

1. The effects of six local anaesthetics have been studied on the activities of soluble phospholipases A2 (EC 3.1.1.4) and lysophospholipase (EC 3.1.1.5). 2. Phospholipase A2 activity in human seminal plasma towards sonicated radioactively-labelled phosphatidylethanolamine was slightly stimulated a low and inhibited at high concentrations of all anaesthetic compounds employed. The order of decreasing potency was chlorpromazine, dibucaine, tetracaine, lidocaine, cocaine and procaine. In line with previous findings, the mode of inhibition was seen to be competitive with respect to Ca2+. 3. Phospholipase A2 activity in crude venom of Crotalus adamanteus was not affected or slightly stimulated by local anaesthetics up to 10(-2) M concentrations, when egg yolk was used as substrate. However, with sonicated radioactively-labelled phosphatidylcholine or phosphatidylethanolamine as substrate, stimulation of phospholipase activity was seen with all local anaesthetics up to 10(-2) M, the order of decreasing potency again being chlorpromazine, dibucaine, tetracaine, lidocaine, cocaine and procaine. The mode of stimulation was seen to be un-competitive with respect to substrate and probably independent of any involvement of Ca2+. 4. As in seminal plasma phospholipase A2, the activity in crude Naja naja venom towards sonicated radioactively labelled phosphatidylcholine was stimulated at low and inhibited at high concentrations of dibucaine and chloropromazine, for example. The mode of inhibition was seen to be competitive with respect to Ca2+, whereas stimulation by the anaesthetic drugs was independent of Ca2+. Binding between drug and enzyme was demonstrated by equilibration filtration of purified phospholipase A2 of Naja naja venom through a Sephadex G 25-fine column, previously equilibrated with 0.5 mM radioactively labelled chlorpromazine. 5. Lysophospholipase activity in rat liver cytosol towards radioactively labelled lysophosphatidylcholine was inhibited by all local anaesthetics used; the order of decreasing potency was chlorpromazine, dibucaine, tetracaine, cocaine, lidocaine and procaine. The inhibition was un-competitive with respect to substrate. 6. The inhibitory and stimulatory potencies of the local anaesthetics employed closely parallel their lipid solubilities and anaesthetic potencies.

Effects of local anaesthetics on the lipase of Rhizopus arrhizus

1. A number of local anaesthetics were shown to inhibit the hydrolytic activity of a partially purified lipase from the mold Rhizopus arrhizur towards both triacylglycerol and phospholipid substrates. 2. Irrespective of whether triacylglycerol or phospholipid substrates were used, the inhibition was uncompetitive with respect to the substrate, independent of Ca2+ concentration, but pH dependent. 3. The inhibitory activity of the local anaesthetics studied closely paralleled the anaesthetic potency of the compounds.

Change of mitochondrial buffering capacity induced by propranolol

Propranolol is able to increase the amount of the titratable groups of mitochondrial membranes. This effect occurs with sonicated particles and with liposomes, too. The phenomenon is only seen in the presence of salt solutions, not in sucrose. Propranolol increases the fluorescence of anilino-naphthalene sulphonate (ANS) in mitochondrial suspensions. The increase is counteracted by increasing concentrations of potassium chloride. It is suggested that the increase of the titratable groups results from a decrease of the aggregation of the phospholipids of the membranes. At the same time the environment of the bound ANS molecules is more hydrophobic in sucrose than in potassium chloride. The amount of the buffering groups and the hydrophilicity are in direct and the amount of the buffering groups and the fluorescence of ANS in inverse correlation.