[Serotonin, 5-hydroxyindolylacetic acid and cholesterol content in blood, cerebrospinal fluid and brain areas for differentiation of suicidal from non-suicidal cause of death]

In the present study serotonin and its metabolite 5-hydroxyindoleacetic acid was investigated in the cerebrospinal fluid and in discrete brain areas of the left and right hemisphere collected from 34 bodies. Sixteen subjects were suicide victims, and 18 were matched as controls. Matching was done for gender, age, sex and cause of death. In suicide victims the concentration of 5-hydroxyindoleacetic acid in cerebrospinal fluid (occipital) was significantly decreased whereas there was no difference comparing the particular results established from the various brain areas. Nevertheless, there was a non-significant trend towards a higher concentration of serotonin in the thalamic area and towards a lower level in samples collected from the mesencephalon in suicide brains. In suicide subjects, the level of 5-hydroxyindoleacetic acid was often found to be increased in the hippocampus and to be decreased in the thalamus. A differentiation between suicide and homicide seems promising only on condition that the distribution of serotonin and metabolite concentrations in various brain areas is considered. The amount of total cholesterol in blood is suggested to be of limited value.

Resistance modulation in CHO cells by R-verapamil and bile salts is associated with physical and chemical changes in the cell membrane

OBJECTIVES

Changes in multidrug resistance by resistance modifiers such as R-verapamil cause changes in fluidity of the cell membrane. The extent to which these changes involve structural alterations in membrane lipids has been investigated in CHO cells.

METHODS

Sensitive (AUXB1) and resistant (CH(R)C5) chinese hamster ovary cells (CHO) were grown in culture. Incubations were carried out with R-verapamil (0-10 microM) or the membrane perturbing agents tauro-cheno-deoxycholate (0-1.6 mM, TCDC) and tauro-urso-deoxycholate (0-3.5mM, TUDC). Cell membrane fluidity was determined by electron-paramagnetic resonance spectroscopy and membrane lipids by HPLC and TLC.

RESULTS

The resistant CH(R)C5 subline had a higher cell membrane order (lower fluidity, S = 0.7234) in the interface region of the cell membrane than sensitive AUXB1 cells (S = 0.6984) determined using EPR. The MDR-modulator R-verapamil and TCDC, but not TUDC, lowered cell membrane order in a concentration-dependent manner and increased membrane fluidity of the resistant CH(R)C5 subline. TCDC and R-verapamil were without effect on the cell membrane fluidity of AUXB1 cells. These changes were accompanied by alterations in the fatty acid composition of the plasma membrane. Untreated sensitive AUXB1 cells had higher levels of unsaturated fatty acids than resistant CH(R)C5 cells. In CH(R)C5 cells, R-verapamil increased the content of poly-unsaturated fatty acids and TCDC, but not TUDC, increased the content of mono-unsaturated fatty acids.

CONCLUSIONS

The results demonstrate that resistance modifiers such as verapamil may influence cytostatic drug action by producing structural changes to lipid domains in the plasma membrane.

beta-agonistic bronchodilators: comparison of dose/response in working rat hearts

STUDY OBJECTIVES

Different beta-agonists are compared with regard to their cardiodepressive side effects.

DESIGN

The metaphenolic bronchodilators reproterol, salbutamol, fenoterol, and terbutaline were introduced at a dosage of 0.0005 micromol to a maximum of 10 micromol per gram of heart tissue into the isolated working rat heart under hypoxic conditions, and the response was observed during subsequent reoxygenation. As an index of external heart work, aortic flow was measured. Heart rate, coronary flow, and developed pressure were recorded. At the end of heart perfusion, mitochondria were isolated and analyzed for adenosine triphosphatase activity, adenosine triphosphate (ATP) synthesis, and membrane fluidity. Moreover, intact mitochondria and lipid peroxidation were investigated using a model system.

MEASUREMENTS AND RESULTS

Compared to controls, reproterol gave the most favorable results, with an increase of 25 to 30% of aortic flow during reoxygenation at a concentration of 10 micromol/g heart tissue. In contrast, both fenoterol and salbutamol at a concentration of 1 micromol/g heart tissue decreased aortic flow during reoxygenation, whereas terbutaline had a negative influence on aortic flow at 0.01 to 0.1 micromol/g heart tissue. Mitochondria of these hearts were isolated at the end of the experiment. Mitochondrial ATP synthesis was increased above controls at nearly all concentrations of reproterol. ATP synthesis was decreased at 1 micromol and 10 micromol fenoterol. As little as 0.0005 micromol terbutaline decreased ATP synthesis by 50%. In intact mitochondria, adenosine diphosphate (ADP) to oxygen ratios were found to be increased with terbutaline and fenoterol, indicating ADP consumption by myokinase activation. Lipid peroxidation was increased in a model system between concentrations of 0.002 micromol/mg and 0.04 micromol/mg phosphatidylcholine by fenoterol and terbutaline, whereas a decrease was noted with reproterol. Membrane fluidity was found increased after addition of reproterol, which supports the evidence of efficient ATP synthesis by this compound.

CONCLUSIONS

Cardiodepressive side effects and greater toxicity of fenoterol and terbutaline were found under the conditions of our experiment. Salbutamol and, in particular, reproterol appear much better tolerated. In addition to partial beta-adrenergic agonism, reproterol may exert an inhibitory influence on adenosine receptor sites and phosphodiesterase, which could result in membrane stabilization by saving cyclic adenosine monophosphate or ATP.

Characterization of the sialic acid binding activity of transmissible gastroenteritis coronavirus by analysis of haemagglutination-deficient mutants

Transmissible gastroenteritis coronavirus (TGEV) agglutinates erythrocytes of several species by virtue of sialic acid binding activity of the surface protein S. We have isolated and characterized five haemagglutination-defective (HAD) mutants. In contrast to the parental virus, the mutants were unable to bind to porcine submandibulary mucin, a substrate rich in sialic acid. Each of the mutants was found to contain a single point mutation in the S protein (Cys155Phe, Met195Val, Arg196Ser, Asp208Asn or Leu209Pro), indicating that these amino acids are affecting the sialic acid binding site. In four of the HAD mutants a nearby antigenic site is affected in addition to the sialic acid binding site, as indicated by reactivity with monoclonal antibodies. The parental virus was found to have an increased resistance to the detergent octylglucoside compared to the HAD mutants. This effect depended on cellular sialoglycoconjugates bound to the virion. If the binding of sialylated macromolecules was prevented by neuraminidase treatment, the parental virus was as sensitive to octylglucoside as were the HAD mutants. We discuss the possibility that the sialic acid binding activity helps TGEV to resist detergent-like substances encountered during the gastrointestinal passage and thus facilitates the infection of the intestinal epithelium. An alternative function of the sialic acid binding activity - accessory binding to intestinal tissues - is also discussed.

Small and large unilamellar vesicle membranes as model system for bile acid diffusion in hepatocytes

Uptake of bile acids into the liver cell occurs via active transport or passive diffusion. In a model system, passive diffusion was studied in liposomes using pyranine fluorescence. Rate constants for the diffusion of diverse more polar or more apolar bile acids were examined. Hydrophobic lithocholic acid (LCA) revealed a maximal rate constant of 0.057 s(-1); with the polar ursodeoxycholic acid (UDCA), the value was 0.019 s(-1). UDCA (3 mol%) effectively decreased the rate constant of 0.1 mM chenodeoxycholic acid (CDCA), whereas cholesterol reached a similar decrease only between 5 and 10 mol%. At higher concentrations of CDCA (above 1 mM) or LCA (0.3-0.4 mM), breaking up of liposomal structure was confirmed by light-scattering decrease and increase of carboxyfluorescein fluorescence. Changes in lipid composition of phosphatidylcholine (PC)- small unilamellar vesicles (SUVs) or large unilamellar vesicles (LUVs) also caused decreasing rate constants. For a cardiolipin (CL):PC ratio of 1:20 the CDCA (0.1 mM) rate constant was 71% lower (0.015 s(-1)) and for a sphingomyelin (SM):PC ratio of 2:1 the rate constant was 50% lower (0.026 s(-1)). Changes in membrane fluidity were detected using membrane anisotropy measurements with the 1,6-diphenyl-1,3, 5-hexatriene (DPH) method. Membrane fluidity was reduced with cholesterol- but not with CL- or SM-containing SUVs (ratio: cholesterol, CL, SM:PC of 1:5). This model system is currently used for the analysis of more complex lipid vesicles resembling the plasma/hepatocyte membrane, which is either stabilized or destabilized by appropriate conditions. The results should become clinically relevant.

Cloning and characterization of gp36, a human mucin-type glycoprotein preferentially expressed in vascular endothelium

A mucin-type glycoprotein has been described in murine, rat and canine tissues as a differentiation antigen and influenza-virus receptor. We have cloned a cDNA from human placenta RNA encoding the corresponding human protein, a type-I integral membrane protein of 162 amino acids. Madin-Darby canine kidney cells transfected with the cDNA clone directed the cell-surface expression of a 36-kDa O-glycosylated sialoglycoprotein, gp36, and two minor isoforms of 28 and 70 kDa. gp36 has a broad tissue distribution with strong expression in lung, placenta and skeletal muscle, as shown by PCR screening of different cDNA libraries. Immunohistochemical detection of gp36 in cryo-sections of human placenta, kidney, lung and nasal polyps showed that the glycoprotein is expressed at the apical plasma membrane of vascular endothelial cells. Expression of gp36 was not restricted to endothelial cells, as alveolar epithelial cells were found to express gp36 as well.

Primary pleomorphic adenoma of the external auditory canal diagnosed by fine needle aspiration cytology. A case report

BACKGROUND

Pleomorphic adenoma (PA) arising in the external auditory canal (EAC) is a very rare neoplasm, thought to be derived from ceruminous glands.

CASE

A 43-year-old male presented with a slowly growing mass in the right EAC. Clinical and radiologic examinations showed a well-circumscribed tumor limited to the EAC, without a connection to the parotid gland. Fine needle aspiration cytology (FNAC) revealed the typical cytologic findings of PA. The diagnosis was confirmed by histologic examination.

CONCLUSION

This case illustrates that together with clinical and radiologic findings, primary PA of the EAC can confidently be diagnosed by FNAC.

The effect of bile salts and calcium on isolated rat liver mitochondria

Intact mitochondria were incubated with and without calcium in solutions of chenodeoxycholate, ursodeoxycholate, or their conjugates. Glutamate dehydrogenase, protein and phospholipid release were measured. Alterations in membrane and organelle structure were investigated by electron paramagnetic resonance spectroscopy. Chenodeoxycholate enhanced enzyme liberation, solubilized protein and phospholipid, and increased protein spin label mobility and the polarity of the hydrophobic membrane interior, whereas ursodeoxycholate and its conjugates did not damage mitochondria. Preincubation with ursodeoxycholate or its conjugate tauroursodeoxycholate for 20 min partially prevented damage by chenodeoxycholate. Extended preincubation even with 1 mM ursodeoxycholate could no longer prevent structural damage. Calcium (from 0.01 mM upward) augmented the damaging effect of chenodeoxycholate (0.15-0.5 mM). The combined action of 0.01 mM calcium and 0.15 mM chenodeoxycholate was reversed by ursodeoxycholate only, not by its conjugates tauroursodeoxycholate and glycoursodeoxycholate. In conclusion, ursodeoxycholate partially prevents chenodeoxycholate-induced glutamate dehydrogenase release from liver cell mitochondria by membrane stabilization. This holds for shorter times and at concentrations below 0.5 mM only, indicating that the different constitution of protein-rich mitochondrial membranes does not allow optimal stabilization such as has been seen in phospholipid- and cholesterol-rich hepatocyte cell membranes, investigated previously.

Hemodynamics and mitochondrial energy metabolism in right heart hypertrophy after acute hypoxic stress

Excessive right heart hypertrophy was investigated under additional acute hypoxic stress to find out a possible contribution of mitochondrial dysfunction to sudden heart failure. Severe right heart hypertrophy in rats was induced by exposure to hypobaric pressure (46,663 Pa) for 4 weeks. Heart rate, isovolumic pressure and coronary flow were determined in the Langendorff mode of perfusion. After normoxia, the hearts were subdued to acute hypoxia/reoxygenation. Mitochondrial membrane potential was measured at the heart surface by fluorometry using 2-(dimethylaminostyryl)-l-ethylpyridinium iodide (DASPEI). At the end of each experiment mitochondria were isolated and ATP synthesis, ATPase, as well as creatine kinase activity were determined. Compared to normal hearts the heart rate is decreased in the hypertrophied group whereas right ventricular systolic and (end)diastolic pressure (adjusted to isovolumetric maxima) are increased. Coronary flow is decreased. Cytosolic creatine phosphate ATP levels and ATP/ADP ratios are significantly (p < 0.01) decreased. Furthermore, ATP synthesis and creatine kinase activities are diminished. At high ADP, respiration is loosely coupled or partially uncoupled. Acute hypoxia is particularly deleterious to hypertrophied hearts: Mitochondrial membrane potential as measured by heart surface fluorometry decreases extensively and is only very incompletely restored during reoxygenation. Rate-pressure product decreases precipitously and is restored during reoxygenation only to a very low extent. The results indicate an insufficient energy metabolism of mitochondria during acute hypoxia/reoxygenation which adds to the earlier described shifted isozyme pattern of myosin and decreased activities of myosin and sarcoreticular Ca2+ ATPase, leading to myocardial failure in right heart hypertrophy.

[Fatal incidences during arrest of highly agitated persons]

We report on four cases of sudden circulatory arrest during the physical restraint of extremely excited and repugnant men by the police. Three persons died, and one became apallic. The excited states resulted from acute schizophrenic disorder in one case, from intoxications (ethanol and drugs including cocaine respectively) in two others, and from encephalitis in the fourth case. In only one case one of the police officers was condemned for involuntary mansloughter, responsability was excluded in the remainder. Similar lethal events in "excited delirium" are given in the American literature, the main etiologic factors being acute psychosis and cocaine intoxication. Most of these events occurred, differing from ours, under "hogtying" which is a technique of physical restraint in a prone position with the wrists and ankles bound behind the back. These events are thought to be cardiac in origin and to result from oxygen-consuming motor hyperactivity, excessive catecholamine release, and impaired breathing. Police officers are recommended to restrict all measures of restraint to a mininum in extremely excited persons, and to avoid any compression of the trunk or neck. A continuous monitoring for vital signs is postulated in order to recognize a medical incident as quick as possible.

Characterization of cross-link density in technical elastomers by the NMR-MOUSE

NMR is a powerful tool in characterizing cross-link density in elastomers. Conventional NMR, however, restricts the sample geometry and does not allow measurements in presence of ferromagnetic materials. The concept of the MOUSE (mobile universal surface explorer) circumvents these restrictions. This surface sensitive method deals with rather inhomogeneous magnetic fields instead of the highly homogeneous fields normally used in NMR. Therefore, pulse sequences are reinvestigated with respect to their sensitivity towards residual dipolar coupling in elastomers. Examples for investigations of technical elastomers and correlations of NMR results with data from macroscopic mechanical measurements are presented.

Superoxide radical scavenging by phenolic bronchodilators under aprotic and aqueous conditions

Asthmatic airway disease is accompanied by the appearance of inflammatory cells which produce reactive oxygen species (ROS). Therefore, the radical scavenging properties of the bronchodilators reproterol, fenoterol, salbutamol and terbutaline toward superoxide anion radicals and hydroperoxyl radicals were investigated in a model system by electron paramagnetic resonance spectroscopy (EPR) and photometric approaches. The substances under study showed activity in superoxide radical scavenging under aprotic and protic conditions as well. The efficiency of the reaction decreased in the order: fenoterol > salbutamol > reproterol > terbutaline > oxyfedrine when DMSO was used as an aprotic solvent. In an aqueous system, the rate constants decreased in the order: fenoterol > reproterol > salbutamol. It is suggested that the antioxidant effect of these beta2-agonists is an additional advantage in treatment of asthmatic lung disease, reducing the negative consequences of airway inflammation.

Gradual changes in permeability of inner mitochondrial membrane precede the mitochondrial permeability transition

Some compounds are known to induce solute-nonselective permeability of the inner mitochondrial membrane (IMM) in Ca2+-loaded mitochondria. Existing data suggest that this process, following the opening of a mitochondrial permeability transition pore, is preceded by different solute-selective permeable states of IMM. At pH 7, for instance, the K0.5 for Ca2+-induced pore opening is 16 microM, a value 80-fold above a therapeutically relevant shift of intracellular Ca2+ during ischemia in vivo. The present work shows that in the absence of Ca2+, phenylarsine oxide and tetraalkyl thiuram disulfides (TDs) are able to induce a complex sequence of IMM permeability changes. At first, these agents activated an electrogenic K+ influx into the mitochondria. This K+-specific pathway had K0.5 = 35 mM for K+ and was inhibited by bromsulfalein with Ki = 2.5 microM. The inhibitors of mitochondrial KATP channel, ATP and glibenclamide, did not inhibit K+ transport via this pathway. Moreover, 50 microM glibenclamide induced by itself K+ influx into the mitochondria. After the increase in K+ permeability of IMM, mitochondria become increasingly permeable to protons. Mechanisms of H+ leak and nonselective permeability increase could also be different depending on the type of mitochondrial permeability transition (MPT) inducer. Thus, permeabilization of mitochondria induced by phenylarsine oxide was fully prevented by ADP and/or cyclosporin A, whereas TD-induced membrane alterations were insensitive toward these inhibitors. It is suggested that MPT in vivo leading to irreversible apoptosis is irrelevant in reversible ischemia/reperfusion injury.

Postmortem distribution of dihydrocodeine and metabolites in a fatal case of dihydrocodeine intoxication

A report of a fatal dihydrocodeine ingestion under substitution therapy is given. Quantitation of dihydrocodeine, dihydromorphine, N-nordihydrocodeine, dihydrocodeine-6-, dihydromorphine-6- and dihydromorphine-3-glucuronide was performed simultaneously after solid-phase extraction prior to HPLC analysis, and the analytes were detected using their native fluorescence. Postmortem concentrations of blood samples from different sampling sites as well as from liver, kidney and cerebrum are reported. A hair sample was investigated to prove long-term use of the substitute drug. Site-to-site differences of the analytes from blood samples were very small. The partition behavior of the opioid glucuronides depended on the hematocrit value of the particular blood sample. Most important findings seemed that dihydromorphine and dihydromorphine-6-glucuronide concentrations decisively contributed to the toxicity of dihydrocodeine. This case report outlines that in dihydrocodeine related deaths the concentrations of the pharmacologically active metabolites should additionally be determined for reliable interpretation.

The NMR-mouse: construction, excitation, and applications

A mobile nuclear magnetic resonance (NMR) device similar to a bore-hole probe has been developed for applications in materials science and biomedicine. Inhomogeneous polarizing and radio-frequency (rf) magnetic fields are applied to arbitrarily large samples from one side. Different experimental techniques have been tested to measure transverse and longitudinal relaxation times and translational diffusion constants. Good contrast for discrimination of material properties is gained when the residual dipolar coupling is retained in soft matter by avoiding spinlock effects in multi-pulse techniques. Applications to characterization of products from technical elastomers, skin, and coatings on iron sheets are reported.

Oxygen radical generation and enzymatic properties of mitochondria in hypoxia/reoxygenation

The time-dependence of oxygen radical formation and development of enzymatic dysfunction after hypoxia/reoxygenation was investigated in isolated rat liver mitochondria. Generation of oxygen radicals was studied by electron paramagnetic resonance (EPR) spectroscopy using the spin trap DMPO (5,5-dimethyl-l-pyrroline-N-oxide). The spin adduct DMPO-OH was found to be formed from the primarily generated adduct of DMPO with the superoxide anion radical (DMPO-OOH). Hypoxic storage followed by reoxygenation at room temperature resulted in an increased decay rate of the DMPO-OH spin adduct while its steady state concentration remained unchanged. This finding strongly suggests an increased rate of DMPO-OH formation which originally derived from enhanced superoxide anion radical production due to hypoxia/reoxygenation. The enhanced superoxide radical formation seems to be due to dysfunction of respiratory chain enzymes, resulting in increased levels of reductive components. In agreement with that, we found the decrease of respiration control and ATP synthesis activity at a similar time scale as that for DMPO-OH adduct formation. The increase of superoxide radical formation and of the reductive capacity of mitochondria was accompanied by a decrease in membrane order at the polar interface. Oxidative phosphorylation was completely abolished after 30 min of hypoxic storage, whereas ATP synthesis decreased significantly after 15 min of hypoxia.

Effect of the triaminopyridine flupirtine on calcium uptake, membrane potential and ATP synthesis in rat heart mitochondria

1. Flupirtine is an analgesic agent which exhibits neuronal cytoprotective activity and may have value in the treatment of conditions involving cell injury and apoptosis. Since flupirtine has no action on known receptor sites we have investigated the effect of this drug on mitochondrial membrane potential, and the changes in intramitochondrial calcium concentration in particular. 2. The findings show that flupirtine increases Ca2+ uptake in mitochondria in vitro. At clinically relevant flupirtine concentrations, corresponding to flupirtine levels in vitro of 0.2 to 10 nmol mg(-1) mitochondrial protein, there was a 2 to 3 fold increase in mitochondrial calcium levels (P<0.01). At supra-physiological flupirtine concentrations of 20 nmol mg(-1) mitochondrial protein and above, the mitochondrial calcium concentrations were indistinguishable from those in untreated mitochondria. 3. Mitochondrial membrane potential closely paralleled the changes in mitochondrial calcium levels showing a 20% (P<0.01) increase when the flupirtine concentration was raised from 0.2 nmol to 10 nmol mg(-1) mitochondrial protein and a return to control values at 20 nmol mg(-1) protein. 4. The increase in mitochondrial calcium uptake and membrane potential were accompanied by an increase in mitochondrial ATP synthesis (30%; P<0.05) and a similar percentage reduction in mitochondrial volume. 5. Calcium at 80 and 160 nmol mg(-1) mitochondrial protein decreased ATP synthesis by 20-25% (P<0.001). This decrease was prevented or diminished if flupirtine at 10 nmol mg(-1) protein was added before the addition of calcium. 6. Since intracellular levels of flupirtine in intact cells never exceeded 10 nmol mg(-1) mitochondrial protein, these findings are supportive evidence for an in vivo cytoprotective action of flupirtine at the mitochondrial level.

Cardioprotective effects of dihydrolipoic acid and tocopherol in right heart hypertrophy during oxidative stress

Rat hearts hypertrophied by exposure of the animals to low oxygen pressure were perfused by the Langendorff technique. After oxidative stress induced by hypoxia/reoxygenation, functional recovery of the hypertrophied right heart was insufficient when compared to non-hypertrophied controls. Accordingly, mitochondrial membrane potential did not recover sufficiently. There was a positive trend for improvement of the rate-pressure product during reoxygenation in lipoic acid (CAS 1077-28-7; 0.8 mumol/l) treated hearts which was also verified for membrane potential. Adenosine 5'-triphosphate and creatine phosphate contents as well as the ATP/ADP ratio in hypertrophied right ventricle were significantly increased after reoxygenation in hearts treated with lipoic acid. With lipoic acid, there was a significantly higher content of glutathione (oxidized form) after reoxygenation, Ca2+ uptake was significantly increased in mitochondria isolated from hypertrophied right ventricles and treated by 12 nmol/mg protein of lipoic acid. The results reveal a distinct improvement of mitochondrial structure/function by lipoic acid and suggest for therapy a combination with the synergistic free radical scavenging properties of tocopherol (CAS 10191-41-0).

Analysis of polymer materials by surface NMR via the MOUSE

Applications are discussed of a novel NMR device, the NMR MOUSE (mobile universal surface explorer), for characterization of polymers. Different properties of elastomers can be related to an effective transverse relaxation parameter T2eff. Effects of multi-echo sequences influence the decay curve and can be described in terms of B0 inhomogeneity and spin-lock effects. Furthermore, the signal-to-noise ratio (SIN) can be improved by use of steady-state free precession (SSFP) pulse sequences modified for use in inhomogeneous magnetic fields.

Quantitative determination and reversible modification of thiols using imidazolidine biradical disulfide label

Earlier we reported an ESR method of quantitative determination of sulfhydryl groups. The method is based on the application of the imidazoline biradical disulfide label, R1S-SR1, which participates in the reaction of thiol-disulfide exchange followed by dramatic changes in ESR spectra. One of the disadvantages of the application of R1S-SR1 at physiological conditions is the requirement of excess of the biradical compared with thiol content which results in the consumption of the thiols and irreversible damage of the system under study. In the present paper we propose imidazolidine biradical disulfide reagent, R2S-SR2, for ESR determination of thiols and provide an experimental basis for its application. This label has the advantages of the previously used biradical disulfide, R1S-SR1, such as high sensitivity down to 1 microM of thiols even in opaque samples and could possibly be used for reversible modification of proteins and enzymes. The particular properties of the R2S-SR2 are pH-sensitivity of its ESR spectrum, higher stability of the imidazolidine radical fragment towards biological reductants and low concentration of the label sufficient for thiol determination at physiological conditions. The latter makes it possible to use ESR spectroscopy for non-invasive thiol measurements in biological systems, in vivo applications included.

Molecular characterization of gp40, a mucin-type glycoprotein from the apical plasma membrane of Madin-Darby canine kidney cells (type I)

gp40 has been recently identified as a major apical cell-surface sialoglycoprotein of type-I Madin-Darby canine kidney cells, a cell line widely used for the study of polarized transport. The determination of two internal amino acid sequences of the purified glycoprotein by Edman degradation enabled us to isolated the cDNA encoding the 18.6 kDa protein backbone of gp40. Sequence analysis revealed that gp40 is a type-I membrane protein which has several characteristics in common with glycophorin A and other mucin-type glycoproteins. At least 14 serine/threonine residues were found to be used for O-glycosylation. No potential sites for N-glycosylation were detected. gp40 turned out to represent the canine homologue of a cell-surface antigen expressed by various epithelial and non-epithelial cells in rat and mouse. Potential O-glycosylation sites, transmembrane and cytoplasmic domains were found to be highly conserved in the three species. gp40 was detected in canine lung, intestine, kidney, brain and heart but not in liver and spleen. The subline II of Madin-Darby canine kidney cells was found not to express gp40. Stable expression of gp40 in transfected type-II cells revealed that gp40 is predominantly delivered to the apical plasma membrane. N-Glycans and a glycosylphosphatidylinositol anchor, both proposed apical targeting signals, are absent from gp40, indicating that other determinants are responsible for its polarized transport.

Membrane cofactor protein (CD46) is a basolateral protein that is not endocytosed. Importance of the tetrapeptide FTSL at the carboxyl terminus

Membrane cofactor protein (MCP) is a widely distributed complement regulatory protein that is expressed on the basolateral surface of polarized epithelial cells. The basolateral targeting of the BC1 isoform of MCP was analyzed by generating deletion mutants and point mutants within the cytoplasmic tail of 16 amino acids. A sequence of four amino acids, FTSL, was found to be indispensable for the basolateral transport of MCP. This tetrapeptide has two unique features compared with the targeting motifs of other basolateral proteins: (i) it contains a phenylalanine rather than a tyrosine at position 1; (ii) it is located at the very COOH-terminal end. Replacement of the phenylalanine or the leucine by an alanine resulted in a nonpolarized delivery to the cell surface. On the other hand, substitution of a tyrosine for the phenylalanine did not affect the basolateral transport of MCP. The latter mutant, however, was efficiently internalized, whereas the wild type protein was not subject to endocytosis. Our results indicate that the targeting signal YXX-large aliphatic that is involved in various sorting events has been modulated in MCP in such a way that it allows basolateral transport but not endocytosis.