Sodium arsenite affects Na+ transport in the isolated skin of the toad Pleurodema thaul

Arsenic, applied as sodium arsenite (As(III)) to either inner or outer surfaces of the isolated toad skin, dose-dependently decreased the short-circuit current (Isc), potential difference (PD) and sodium conductance (G(Na)) in the concentration range 1-1000 microM, with effects often lasting over 3 h. Maximal inhibitory effect was over 90% with an IC(50) of about 34 microM. Applied during amiloride block, As(III) did not change this effect. However, an increase in electric parameters was noted during the initial 30 min in 22 experiments, indicating a possible translocation of cytosolic protein kinase C (PKC) to the membrane within 15 min, thus stimulating sodium transport; this is followed by a progressive inhibition of kinase activity. Comparative effects of amiloride (8 microM), As(III) (100 microM, outer surface) and noradrenaline (NA, 10 microM, inner surface) showed a significant increase in the stimulatory effect of NA on the electric parameters, which could be the result of arsenite clustering of cell surface receptors and activation of ensuing cellular signal transduction pathways. Ouabain 5 microM, followed by As(III) 100 microM, also stimulated the skin response to NA (10 microM), although the duration of the two phases of the response was markedly shortened. The exact mechanism is still in doubt: however, As(III) increases cerebral metabolites of NA and ouabain can increase NA efflux from tissue slices. The amiloride test, performed with As(III) in the outer surface, confirmed significant decrease in all the parameters: the driving force (E(Na)), sodium conductance (G(Na)), and importantly, shunt conductance (G(sh)), due to the known fact that arsenic inhibits gap junctional intercellular communication.

Arsenite interactions with phospholipid bilayers as molecular models for the human erythrocyte membrane

There are scanty reports concerning the effects of arsenic compounds on the structure and functions of cell membranes. With the aim to better understand the molecular mechanisms of the interaction of arsenite with cell membranes we have utilized bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. The capacity of arsenite to perturb the bilayer structures was determined by X-ray diffraction and fluorescence spectroscopy, whilst the modification of their thermotropic behaviour was followed by differential scanning calorimetry (DSC). The experiments carried out by X-ray diffraction and calorimetry clearly indicated that NaAsO(2) interacted with DMPE and modified its thermotropic behaviour. No such information has been so far reported in the literature.

Effects of the antiepileptic drug carbamazepine on human erythrocytes

The structural effects of the antiepileptic drug carbamazepine (CBZ) on the human erythrocyte membrane and molecular models have been investigated in the present work. This report presents the following evidence that CBZ interacts with red cell membranes: (a) X-ray diffraction and fluorescence spectroscopy of phospholipid bilayers showed that CBZ perturbed a class of lipids found in the outer moiety of the erythrocyte membrane; (b) in isolated unsealed human erythrocytes (IUM) the drug induced a disordering effect on the polar head groups and acyl chains of the membrane lipid bilayer; (c) in scanning electron microscopy (SEM) studies on human erythrocytes the formation of echinocytes was observed, due to the preferential insertion of CBZ in the outer monolayer of the red cell membrane. The effects of the drug detected in the present work were observed at concentrations of the order of those currently appearing in serum when it is therapeutically administered. This is the first time that toxic effects of carbamazepine on the human erythrocyte membrane have been described.

The antiepileptic drug carbamazepine affects sodium transport in toad epithelium

The present work investigates the effects of the antiepileptic drug carbamazepine (CBZ) on sodium transport in the isolated skin of the toad Pleurodema thaul. A submaximal concentration of the drug (0.2 mM) applied to the outer surface of the epithelium increased the electrical parameters short-circuit current (Isc) and potential difference (PD) by over 28%, whereas only a higher concentration (1 mM) induced over a 45% decrease in these parameters when applied to the inner surface. The amiloride test showed that the outer surface stimulatory effect was accompanied by an increase and the inner surface inhibitory effect by a decrease in the sodium electromotive force (ENa). Exploration of these effects of CBZ on the outer surface showed that 0.2 mM increased net Na+ (22Na) influx by 20% and 0.6 mM CBZ decreased Na+ mucosa-serosa flux by 19%, a result in agreement with the finding that higher concentrations of CBZ applied to the inner surface not only decreased ENa but also sodium conductance (GNa).

Protective effect of Ugni molinae Turcz against oxidative damage of human erythrocytes

Ugni molinae Turcz, also known as "Murtilla", is a plant that grows in the south of Chile. Infusions of its leaves have long been used in traditional native herbal medicine. The chemical composition of the leaves indicates the presence of polyphenols, which have antioxidant properties. In the present work, the antioxidant properties of U. molinae were evaluated in human erythrocytes exposed in vitro to oxidative stress induced by HClO. The experiments were carried out by scanning electron microscopy (SEM) and hemolysis measurements. The SEM observations showed that HClO induced a morphological alteration in the red blood cells from a discoid to an echinocytic form. According to the bilayer couple hypothesis, the formation of echinocytes indicates that HClO was inserted in the outer leaflet of the erythrocyte membrane. However, a concentration as low as 10 microM gallic acid equivalents (GAE) U. molinae aqueous extract neutralized the shape change effect of HClO applied in a concentration as high as 0.25 mM. The significant protection of U. molinae aqueous extract was also shown in the hemolysis experiments. In fact, very low concentrations of the extract considerably reduced the deleterious capacity of HClO to induce hemolysis in red blood cells. It is concluded that the location of the extract components into the membrane bilayer and the resulting restriction on its fluidity might hinder the diffusion of HClO and its consequent damaging effects. This conclusion can also imply that this restriction could apply to the diffusion of free radicals into cell membranes and the subsequent decrease of the kinetics of free radical reactions.

Human erythrocytes are affected in vitro by extracts of Ugni molinae leaves

Ugni molinae Turcz, also known as "Murtilla", is a plant that grows in the south of Chile. Infusions of their leaves have long been used in traditional native herbal medicine. The chemical composition of the leaves indicates the presence of polyphenols, which have antioxidant properties. In order to evaluate the mechanisms of their antioxidant properties and the toxicity of the aqueous extracts of leaves, the extracts were induced to interact with human red cells, their isolated unsealed membranes (IUM) and large unilamellar vesicles (LUV) of dimyristoylphosphatidyltidylcholine (DMPC), representative of phospholipid classes located in the outer monolayer of the erythrocyte membrane. Scanning electron microscopy (SEM) observations indicated that the extracts achieved a significant alteration in the shape of the erythrocytes as they changed their discoid shape to echinocytes. According to the bilayer couple hypothesis, the shape change indicates that the polyphenols were located in the outer moiety of the red cell membrane. This conclusion was confirmed by the fluorescence experiments performed in IUM and DMPC LUV. In fact, the extracts produced slight initial increases followed by sharp decreases at higher concentrations in the anisotropy and general polarization parameters. These results imply that the extracts induced structural perturbations in the acyl chain and polar group packing arrangements of the erythrocyte IUM and DMPC LUV lipid bilayers: first ordering and afterwards disordering them as the extract concentration increased.

The antiepileptic drug phenytoin affects sodium transport in toad epithelium

The effects of phenytoin on isolated Pleurodema thaul toad skin were investigated. Low (micromolar) concentrations of the antiepileptic agent applied to the outside surface of the toad epithelium increased the electrical parameters (short-circuit current and potential difference) by over 40%, reflecting stimulation of Na(+) transport, whereas higher (millimolar concentrations, outside and inside surface) decreased both electric parameters, the effect being greater at the inside surface (40% and 80% decrease, respectively). The amiloride test showed that the stimulatory effect was accompanied by an increase and the inhibitory effect by a decrease in the sodium electromotive force (ENa). It is concluded that the drug interaction with membrane lipid bilayers might result in a distortion of the lipid-protein interface contributing to disturbance of Na(+) epithelial channel activity. After applying the Na(+)-K(+)-ATPase blocker ouabain and replacing the Na(+) ions in the outer Ringer's solution by choline, it was concluded that both active and passive transport are involved in sodium absorption, although active transport predominates.

Effects of cadmium on Na+ transport in the isolated skin of the toad Pleurodema thaul

Cadmium ions applied to either (outer or inner) surface of the isolated toad skin dose-dependently increased the short-circuit current (SCC), the potential difference (V) and the active sodium conductance (G(Na)) in the concentration range 0.07-0.50mM. Maximal stimulatory effect was over 30% with an EC(50) of about 0.1mM. The effect of the highest concentration used (0.75mM) decreased considerably, and when it was applied to the inner surface (10 experiments), induced between 30% and 40% inhibition of the electric parameters in four experiments. Pretreatment with amiloride inverted the stimulatory effect of externally applied Cd(2+), suggesting competitive action on the apical Na(+) channel. The effect of noradrenaline (NA) was increased after outer application of Cd(2+) and decreased after inner application of the metal: the latter effect might be due to cadmium inhibition of the activity of Na(+),K(+)-ATPase. On the other hand, pretreatment with amiloride was followed by partial although transient reversal of its effects by serosal Cd(2+), which might be explained by action of cadmium on cytoplasmic lysine residues concerned with Na(+) channel gating. The amiloride test showed that the increment of the electric parameters was due principally to stimulation of the driving potential for Na(+) (V-E(Na(+))) and that inhibition was accompanied by a reduction in the V-E(Na(+)) and by a significant decrease in skin resistance indicating possible disruption of membrane or cell integrity. These data are in favor of the possibility that externally applied Cd(2+) activates toad skin ion transport, partly by increasing apical sodium conductance and also by stimulating the V-E(Na(+)), and that internally applied Cd(2+), with easier access to membrane and cellular constituents, may inhibit the sodium pump.

A study of the perturbation effects of the local anesthetic procaine on human erythrocyte and model membranes and of modifications of the sodium transport in toad skin

The interaction of the local anesthetic procaine with human erythrocytes, isolated unsealed human erythrocyte membranes (IUM), isolated toad skins, and molecular models is described. The latter consisted of phospholipid multilayers built-up of dimyristoylphosphatidylcholine (DMPC) and of dimyristoylphosphatidylethanolamine (DMPE), representatives of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. Optical and scanning electron microscopy of human erythrocytes revealed that procaine induced the formation of stomatocytes. Experiments performed on IUM at 37 degrees C by fluorescence spectroscopy showed that procaine interacted with the phospholipid bilayer polar groups but not with the hydrophobic acyl chains. X-ray diffraction indicated that procaine perturbed DMPC structure to a higher extent when compared with DMPE, its polar head region being more affected. Electrophysiological measurements disclosed a significant decrease in the potential difference (PD) and in the short-circuit current (Isc) after the application of procaine to isolated toad skin, reflecting inhibition of active ion transport.

Human erythrocytes are affected by the organochloride insecticide chlordane

Chlordane is a widely used organochlorine insecticide. In order to evaluate its perturbing effect upon the morphology of human erythrocytes it was caused to interact with human red cells and molecular models of cell membranes. These consisted in bilayers of dimyristoylphosphatidylethanolamine (DMPE) and of dimyristoylphosphatidylcholine (DMPC), representative of phospholipid classes located in the inner and outer monolayers of the erythrocyte membrane, respectively. Scanning electron microscopy (SEM) observations indicated that this pesticide induced a significant alteration in the shape of the erythrocytes as they changed their discoid shape to spherocytes. According to the bilayer couple hypothesis, the shape changes induced in erythrocytes by foreign molecules are due to differential expansion of their two monolayers. The fact that chlordane produced spherocytes would indicate that the pesticide was equally located in the outer and the inner moieties of the red cell membrane. This conclusion was supported by the results obtained from X-ray diffraction studies. These showed that the hydrophobic and polar head regions of DMPC bilayers were perturbed when the insecticide was in a 1:10 molar ratio with respect to the lipid. These results were confirmed by the fluorescence experiments performed in DMPC large unilamellar vesicles (LUV). Chlordane produced a sharp decrease in the anisotropy and general polarization parameters in the 0-0.1 mM range, implying an increase in the fluidity at the acyl chain and polar region of DMPC. On the other hand, the bilayer structure of DMPE was perturbed in a fashion similar to that observed by X-ray diffraction in DMPC, a fact that explains the morphological change induced by chlordane to the human erythrocytes.

Structural effects of titanium citrate on the human erythrocyte membrane

The structural effects of titanium citrate on the human erythrocyte membrane were studied through its interaction with intact erythrocytes and isolated unsealed human erythrocyte membranes (IUM). The studies were carried out by scanning electron microscopy and fluorescence spectroscopy, respectively. Titanium citrate induced shape changes in erythrocytes, which were damaged and ruptured leaving empty and retracted membranes. Fluorescence spectroscopy measurements in IUM indicated a disordering effect at both the polar head group and the acyl chain packing arrangements of the membrane phospholipid bilayer. Titanium citrate also interacted with molecular models of the erythrocyte membrane consisting in bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representing classes of phospholipids located in the outer and inner monolayers of the erythrocyte membrane, respectively. X-ray diffraction indicated that titanium citrate induced structural perturbation of the polar head group and of the hydrophobic acyl regions of DMPC, while the effects on DMPE bilayers were negligible. This conclusion is supported by fluorescence spectroscopy measurements on DMPC large unilamellar vesicles. All these findings indicate that the structural perturbations induced by titanium to human erythrocytes can be extended to other cells, thereby affecting their functions.

Evidence for the hydration effect at the semiconductor phospholipid-bilayer interface by TiO2 photocatalysis

The interactions of TiO2 with phospholipid bilayers found in cell membrane walls were observed to perturb the bilayer structure under UVA light irradiation. The structure changes in the phospholipid bilayers upon contact with TiO2 under light and in the dark were followed by X-ray diffraction. Hydration effects at the semiconductor-phospholipid interface played an important role in the degradation of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) bilayers taken as cell wall lipid bilayer models. Evidence is provided that the fluidity of the phospholipid bilayers plays a significant role when interacting in the dark with the TiO2 or in processes mediated by TiO2 under light irradiation.

Iron affects the structure of cell membrane molecular models

The effects of Fe(3+) and Fe(2+) on molecular models of biomembranes were investigated. These consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and of dimyristoylphosphatidylethanolamine (DMPE), classes of phospholipids located in the outer and inner moieties of cell membranes, respectively. X-ray studies showed that very low concentrations of Fe(3+) affected DMPC organization and 10(-3)M induced a total loss of its multilamellar periodic stacking. Experiments carried out with Fe(2+) on DMPC showed weaker effects than those induced by Fe(3+) ions. Similar experiments were performed on DMPE bilayers. Fe(3+) from 10(-7)M up to 10(-4)M had practically no effect on DMPE structure. However, 10(-3)M Fe(3+) induced a deep perturbation of the multilamellar structure of DMPE. However, 10(-3)M Fe(2+) had no effect on DMPE organization practically. Differential scanning calorimetry measurements also revealed different effects of Fe(3+) and Fe(2+) on the phase transition and other thermal properties of the examined lipids. In conclusion, the results obtained indicate that iron ions interact with phospholipid bilayers perturbing their structures. These findings are consistent with the observation that iron ions change cell membrane fluidity and, therefore, affect its functions.

Effects of chronic treatment with sodium tetrachloroaurate(III) in mice and membrane models

Gold is a nonessential element with a variety of applications in medicine. A few gold(I) compounds are used in the clinics for treatment of rheumatoid arthritis and of discoid lupus. Some novel gold(III) compounds are under evaluation as anticancer agents. It is known that gold compounds generally produce toxic effects on the kidneys and characteristic lesions in the brain. However, information concerning the neurotoxicity of gold derivatives in humans as well as in experimental toxicology is rather scarce. For this reason we tried to shed some further light on this aspect of gold neurotoxicity by chronic treatment of mice with sodium tetrachloroaurate(III) in order to observe possible biophysical and morphological alterations that may occur in the brain. Chronic gold treatment resulted in a markedly decreased expression of metallothioneins and of glial fibrillary acidic protein in astrocytes of different brain areas. To examine its effects on cell membranes, interactions of sodium tetrachloroaurate(III) with molecular models were also evaluated. The models consisted in bilayers built-up of classes of phospholipids located in the outer and inner monolayers of biological membranes. Structural perturbation of cell membrane models was observed only at concentrations 10(5) times higher than those detected in the brains of animals after three months' treatment. These results show that toxic effects on animal brain upon treatment with sodium tetrachloroaurate develop with difficulty and may be observed only at high doses.

Effects of Pb2+ ions on Na+ transport in the isolated skin of the toad Pleurodema thaul

The effects induced by lead ions on the short-circuit current (SCC) and on the potential difference (V) of the toad Pleurodema thaul skin were investigated. Pb2+ applied to the outer (mucosal) surface increased SCC and V and when applied to the inner (serosal) surface decreased both parameters. The stimulatory effect, but not the inhibitory action, was reversible after washout of the metal ion. The amiloride test showed that the increase was due principally to stimulation of the driving potential for Na+ (V-E(Na+)) and that inhibition was accompanied by a reduction in the V-E(Na+) and also by a significant decrease in skin resistance indicating possible disruption of membrane and/or cell integrity. The effect of noradrenaline was increased by outer and decreased by inner administration of Pb2+. The results suggest that mucosal Pb2+ activates toad skin ion transport by stimulating the V-E(Na+) and that serosal Pb2+, with easier access to membrane and cellular constituents, inactivates this mechanism, revealing greater toxicity when applied to the inner surface of the skin.

The Antiepileptic Drug Diphenylhydantoin Affects the Structure of the Human Erythrocyte Membrane

Phenytoin (diphenylhydantoin) is an antiepileptic agent effective against all types of partial and tonic-clonic seizures. Phenytoin limits the repetitive firing of action potentials evoked by a sustained depolarization of mouse spinal cord neurons maintained in vitro. This effect is mediated by a slowing of the rate of recovery of voltage activated Na+ channels from inactivation. For this reasons it was thought of interest to study the binding affinities of phenytoin with cell membranes and their perturbing effects upon membrane structures. The effects of phenytoin on the human erythrocyte membrane and molecular models have been investigated in the present work. This report presents the following evidence that phenytoin interacts with cell membranes: a) X-ray diffraction and fluorescence spectroscopy of phospholipid bilayers showed that phenytoin perturbed a class of lipids found in the outer moiety of cell membranes; b) in isolated unsealed human erythrocyte membranes (IUM) the drug induced a disordering effect on the polar head groups and acyl chains of the erythrocyte membrane lipid bilayer; c) in scanning electron microscopy (SEM) studies on human erythrocytes the formation of echinocytes was observed, due to the insertion of phenytoin in the outer monolayer of the red cell membrane. This is the first time that an effect of phenytoin on the red cell shape is described. However, the effects of the drug were observed at concentrations higher than those currently found in plasma when phenytoin is therapeutically administered.

Cadmium-induced changes in the membrane of human erythrocytes and molecular models

The structural effects of cadmium on cell membranes were studied through the interaction of Cd(2+) ions with human erythrocytes and their isolated unsealed membranes (IUM). Studies were carried out by scanning electron microscopy and fluorescence spectroscopy, respectively. Cd(2+) induced shape changes in erythrocytes, which took the form of echinocytes. According to the bilayer couple hypothesis, this result meant that Cd(2+) ions located in the outer monolayer of the erythrocyte membrane. Fluorescence spectroscopy measurements in IUM indicated a disordering effect at both the polar headgroup and the acyl chain packing arrangements of the membrane phospholipid bilayer. Cd(2+) ions also interacted with molecular models of the erythrocyte membrane consisting in bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representing classes of phospholipids located in the outer and inner monolayers the erythrocyte membrane, respectively. X-ray diffraction indicated that Cd(2+) ions induced structural perturbation of the polar headgroup and of the hydrophobic acyl regions of DMPC, while the effects of cadmium on DMPE bilayers were much milder. This conclusion is supported by fluorescence spectroscopy measurements on DMPC large unilamellar vesicles (LUV). All these findings point to the important role of phospholipid bilayers in the interaction of cadmium on cell membranes.

Aluminum fluoride affects the structure and functions of cell membranes

No useful biological function for aluminum has been found. To the contrary, it might play an important role in several pathologies, which could be related to its interactions with cell membranes. On the other hand, fluoride is a normal component of body fluids, soft tissues, bones and teeth. Its sodium salt is frequently added to drinking water to prevent dental caries. However, large doses cause severe pathological alterations. In view of the toxicity of Al(3+) and F(-) ions, it was thought of interest to explore the damaging effects that AlF(3) might induce in cell membranes. With this aim, it was incubated with human erythrocytes, which were examined by phase contrast and scanning electron microscopy, and molecular models of biomembranes. The latter consisted of large unilamellar vesicles (LUV) of dimyristoylphosphatidylcholine (DMPC) and bilayers of DMPC and dimyristoylphosphatidylethanolamine (DMPE) which were studied by fluorescence spectroscopy and X-ray diffraction, respectively. In order to understand the effects of AlF(3) on ion transport (principally sodium and chloride) we used the isolated toad skin to which electrophysiological measurements were applied. It was found that AlF(3) altered the shape of erythrocytes inducing the formation of echinocytes. This effect was explained by X-ray diffraction which revealed that AlF(3) perturbed the structure of DMPC, class of lipids located in the outer monolayer of the erythrocyte membrane. This result was confirmed by fluorescence spectroscopy on DMPC LUV. The biphasic (stimulatory followed by inhibitory) effects on the isolated skin suggested changes in apical Cl(-) secretion and moderate ATPase inactivation.

Effects of the local anesthetic benzocaine on the human erythrocyte membrane and molecular models

The interaction of the local anesthetic benzocaine with the human erythrocyte membrane and molecular models is described. The latter consisted of isolated unsealed human erythrocyte membranes (IUM), large unilamellar vesicles (LUV) of dimyristoylphospatidylcholine (DMPC), and phospholipid multilayers of DMPC and dimyristoylphospatidyletanolamine (DMPE), representatives of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. Optical and scanning electron microscopy of human erythrocytes revealed that benzocaine induced the formation of echinocytes. Experiments performed on IUM and DMPC LUV by fluorescence spectroscopy showed that benzocaine interacted with the phospholipid bilayer polar groups and hydrophobic acyl chains. X-ray diffraction analysis of DMPC confirmed these results and showed that benzocaine had no effects on DMPE. The effect on sodium transport was also studied using the isolated toad skin. Electrophysiological measurements indicated a significant decrease in the potential difference (PD) and in the short-circuit current (Isc) after the application of benzocaine, reflecting inhibition of active ion transport.

Effects of lead on the human erythrocyte membrane and molecular models

Lead has no biological function; however, low, and particularly, high levels of exposure have a number of negative consequences for human health. Despite the number of reports about lead toxicity, very little information has been obtained regarding its effects on cell membranes. For this reason, the structural effects of lead on the human erythrocyte membranes were investigated. This aim was attained by making lead ions interact with intact erythrocytes, isolated unsealed erythrocyte membranes (IUM) and molecular models. The latter consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representing phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane. The results, obtained by electron microscopy, fluorescence spectroscopy and X-ray diffraction, indicated that (a) lead particles adhered to the external and internal surfaces of the human erythrocyte membrane; (b) lead ions disturbed the lamellar organization of IUM and DMPC large unilamellar vesicles (LUV) and (c) induced considerable molecular disorder in both lipid multilayers, the effects being much more pronounced in DMPC.

The toxicity of exposure to the organochlorine, dieldrin, at a sympathetic junction and on the skin of the frog, Caudiverbera caudiverbera

The effects of the organochlorine, dieldrin, were tested on a noradrenergic synapse of the frog, Caudiverbera caudiverbera. Nerve stimulation induced a transient increase in short circuit current (SCC) and in the potential difference (PD), which consisted of a rapid and then a slow component. Dieldrin in the concentration range 0.01-1.0 mM caused a concentration-dependent block of both components to 32% of their control values, which was partially reversed by washout. In some experiments, this blocking effect was preceded by an initial increase in the magnitude of the electrical parameters of the nonstimulated skin and also in the synaptic response to stimulation when the lowest dieldrin concentration (0.01 mM) was applied; higher concentrations (0.1-1.0 mM) led to progressive reduction of the responses. Results are interpreted as a perturbation of the lipid bilayer structure, which affects the functionality of lipid-protein complexes, leading, on one hand, to glandular Cl- channel inactivation and epithelial Na+ channel blockade and, on the other hand, to transient glandular Cl- activation, opening of a putative Na+ channel, and subsequent blockade.

The local anesthetic proparacaine modifies sodium transport in toad skin and perturbs the structures of model and cell membranes

Experimental results indicate a significant decrease in the potential difference (PD) and in the short-circuit current (Isc) after the application of proparacaine to isolated toad skin, which may reflect an inhibition of the active transport of ions. This finding was explained on the basis of the results obtained from membrane models incubated with proparacaine. These consisted of human erythrocytes, isolated unsealed human erythrocyte membranes (IUM), phospholipid multilayers built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representatives of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively, and in large unilamellar vesicles (LUV) of DMPC X-ray diffraction showed that proparacaine interaction with DMPC and DMPE bilayers perturbed both structures, especially DMPC. This result, confirmed by fluorescence spectroscopy of DMPC LUV at 18 degrees C, demonstrated that the local anesthetic (LA) could interact with the lipid moiety of cell membranes. However, effects observed by scanning electron microscopy (SEM) of human erythrocytes and by fluorescence spectroscopy of IUM might also imply proparacaine-protein interactions. Thus, the LA may alter epitheial sodium channels through interaction with the lipid matrix and with channel protein residues.

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

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