Identification of the ubiquitous human desmoglein, Dsg2, and the expression catalogue of the desmoglein subfamily of desmosomal cadherins

Desmosomes are junctions between epithelial, myocardiac, and certain other kinds of cells. They represent plasma membrane domains enriched in specific transmembrane glycoproteins, notably desmoglein (Dsg) and desmocollin (Dsc), both of which have recently been identified as members of the larger family of Ca(2+)-dependent cell adhesion molecules, the cadherins. Previously described forms of desmoglein have been isolated as proteins and cloned as cDNAs from epidermis and related stratified epithelia but have not been detected in the majority of other desmosome-containing tissues and cell culture lines. Here we present the complete cDNA-derived amino acid (aa) sequence of a different desmoglein polypeptide, termed Dsg2 (1069 aa, mol wt 116,760) and its precursor molecule (1117 aa, mol wt 122,384), which occurs in all human and bovine desmosome-producing tissues, tumors, and cell lines examined, epithelial as well as nonepithelial ones. We conclude that Dsg2, the largest molecule in this protein family, is the fundamental desmoglein common to all desmosome-possessing tissues, including simple epithelia and myocardium, and many cell cultures. Furthermore, in several tissues and cell lines Dsg2 is the only Dsg isoform detected so far. By contrast, the epidermal isoforms Dsg1 and Dsg3 are restricted to certain specialized epithelia, mostly stratified squamous ones. The importance of the junction-specific cadherin Dsg2 in tissue formation and carcinogenesis as well as in the development of autoimmune diseases of the Pemphigus type is discussed. In addition, we propose to use Dsg2 as a general marker common to all epithelial cells and tumors and to use the specific pattern of occurrence of Dsg and Dsc isoforms as an additional criterion for cell typing in tumor diagnosis.

2,3,7,8-Tetrachlorodibenzo-p-dioxin as growth modulator in mouse hepatocytes with high and low affinity Ah receptor

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a highly potent tumor promoter in rodent liver, has been shown to increase epidermal growth factor (EGF)-stimulated DNA synthesis in rat hepatocytes in primary culture, a comitogenic effect possibly linked to the mechanism of liver tumor promotion. In hepatocytes isolated from male congenic mice (C57BL/6J) with high-affinity (AhbAhb) or low-affinity (AhdAhd) Ah receptor the association of the comitogenic action of TCDD with the Ah receptor was investigated. The potency of TCDD as inducer of CYP1A-catalyzed 7-ethoxyresorufin O-deethylase (EROD) activity was approximately 10-fold lower in AhdAhd compared to AhbAhb cells. In both cell types, TCDD did not stimulate DNA synthesis in the absence of EGF. When added together with EGF, TCDD exhibited two opposing effects on DNA synthesis, measured as incorporation of [3H]thymidine into DNA: (i) At 3 x 10(-14) M, TCDD increased EGF-stimulated DNA synthesis approximately 1.4-fold in AhbAhb but not in AhdAhd cells at a plating density of 35,000 cells/cm2. In hepatocytes from AhdAhd mice, 3 x 10(-12) M TCDD was required to elicit a similar comitogenic response. (ii) At a density of 10,000 cells/cm2, 3 x 10(-12) M TCDD had a pronounced inhibitory effect on EGF-stimulated DNA synthesis in AhbAhb but not in AhdAhd cells. Essentially similar results were obtained by counting of 5-bromo-2'-deoxyuridine-labeled nuclei. These findings demonstrate that TCDD can enhance or antagonize EGF-stimulated DNA synthesis in mouse hepatocytes modified by the cell density. The different concentration-response relationships in hepatocytes from both strains suggest that the Ah receptor regulates these responses.

Desmosomes--dual junctional principles of intra- and supracellular order in epithelial differentiation and tissue formation

The cells of most normal and malignantly growing tissues are connected by "adhering junctions", i.e. distinct sites of "homotypic" contact between the plasma membranes of two cells of the same or a similar kind, associated on the cytoplasmic side by a dense plaque at which often bundles of cytoskeletal filaments anchor. Of the various types of adhering junctions desmosomes are characteristic of epithelia and carcinomas but also occur in some other cell types. Their molecular components have recently been identified and characterized by cDNA-cloning and sequencing. Unexpectedly, the molecular complement of desmosomes has been found to show certain differences in different epithelia, with particularly complex patterns in stratified squamous epithelia as well as in tumors and cultured cell lines derived therefrom. In addition, molecular principles important in the assembly of desmosomes and in the specific anchorage of intermediate-sized filaments (IFs) at desmosomal plaques have been elucidated. The possible value of cell type-specific isoforms of desmosomal components as markers for the subtyping of carcinomas and the role of desmosomal cadherins during invasion and metastasis of carcinomas are discussed.

Cytoskeletal architecture and epithelial differentiation: molecular determinants of cell interaction and cytoskeletal filament anchorage

Desmosomes are morphologically well defined junctions between epithelial cells and also some other cells such as myocardiocytes, meningeal cells and dendritic reticulum cells of lymphatic follicles. Besides their function in cell coupling, desmosomes anchor components of the cytoskeleton, i.e. intermediate-sized filaments (IFs), through their cytoplasmic plaques, thereby contributing to cytoskeletal and tissue architecture. In molecular terms, desmosomes are specific assemblies of transmembrane glycoproteins of the cadherin family, desmoglein(s) and desmocollin(s), that contribute to cell adhesion via their extracellular, aminoterminal domains and to plaque formation and IF coupling through their cytoplasmic, carboxyterminal "tails". Using transfection assays, we analyzed the function of different tail domains in plaque assembly and IF anchorage. Furthermore, we present evidence that both desmogleins and desmocollins represent multigene subfamilies showing cell type specific expression and that a desmosomal plaque protein occurring in stratified and complex epithelia, the "band 6 protein", is related to the plakoglobin family.

Adenosine A2-receptor activation at reperfusion reduces infarct size and improves myocardial wall function in dog heart

Reestablishment of blood supply to ischemic myocardium leads to biochemical and cellular changes which are believed to reduce the amount of potentially salvageable myocardium (reperfusion injury). In this situation, adenosine is known to have myocardial protective properties. Activation of adenosine A2-receptors may account for most of the beneficial effects of adenosine in reperfusion injury because A2-receptor activation mediates vasodilation, inhibits neutrophil adhesion to vascular endothelium and diminishes generation of free radicals by neutrophils, thus acting on some of the key mechanisms of reperfusion injury such as postischemic vascular dysfunction and neutrophil-mediated damage. Therefore, we investigated the effect of an intracoronary A2-agonist, CGS 21680, on regional postischemic myocardial function (measured as wall thickening) and infarct size [determined by triphenyltetrazolium chloride (TTC) staining]. Fourteen anesthetized open-chest dogs underwent 1-h left anterior descending artery (LAD) occlusion and 6-h reperfusion and were randomly assigned to receive intracoronary CGS 21680 or to serve as control. The drug was infused for 60 min starting 5 min before reperfusion with a concentration of 10(-7) M at a rate of 10 ml/min under anoxic conditions. The infusion was then continued for the first 55 min of reperfusion with 10(-6) M at a rate of 1 ml/min. Intracoronary infusion of CGS 21680 led to significant improvement in regional wall function in postischemic myocardium (p < 0.05 vs. control). Thickening fraction (percentage of baseline) increased from -13.1 +/- 13.7% (mean +/- SD) during occlusion to 15.3 +/- 29.8% at 30 min of reperfusion in the CGS 21680 treatment group and remained at this level throughout the reperfusion period.(ABSTRACT TRUNCATED AT 250 WORDS)

Afterload dependent prolongation of left ventricular relaxation: importance of asynchrony

OBJECTIVE

Acute increases in afterload and in left ventricular asynchrony both independently prolong left ventricular isovolumetric relaxation. The aim of the study was to investigate whether an increased left ventricular afterload augments left ventricular asynchrony, which in turn could mediate the afterload dependent prolongation of left ventricular isovolumetric relaxation.

METHODS

Seven chloralose anaesthetised open chest dogs were instrumented with a left ventricular pressure gauge and two pairs of ultrasonic wall thickness crystals in the antero-apical and postero-basal left ventricular wall. At a constant heart rate of 149(SEM 7) beats.min-1, left ventricular pressure was acutely increased by brief manual clamping of the descending (AOCD) and ascending AOCA) thoracic aorta. Left ventricular asynchrony was quantified by the phase difference of the first Fourier harmonic between postero-basal and antero-apical wall motion. Global left ventricular relaxation was measured as the time constant of isovolumetric pressure fall, tau. Regional myocardial relaxation was assessed as the mean rate to half end diastolic thinning.

RESULTS

AOCD increased left ventricular peak systolic pressure from 141.9(6.9) mm Hg to a maximum of 182.0(5.1) mm Hg and tau from 34.3(2.4) ms to 48.0(5.0) ms (p less than 0.05). Simultaneously, phase difference increased markedly during AOCD, from 12.7(3.5) degrees to 24.4(2.2) degrees (p less than 0.05). At matched left ventricular peak systolic pressures, AOCA increased tau from 33.4(2.5) ms to only 42.5(4.3) ms (p less than 0.05 v control and AOCD). Concomitantly, the increase in phase difference was smaller and statistically non-significant, at 13.7(2.9) degrees v 17.1(2.5) degrees. During 13 out of the 14 aortic clampings (7 AOCD, 6 AOCA), tau correlated linearly with phase difference [mean r = 0.74(0.03)]. In contrast to their effects on global left ventricular relaxation and asynchrony, neither AOCD nor AOCA influenced the rate to half end diastolic thinning.

CONCLUSIONS

(1) left ventricular asynchrony may increase during an acute augmentation of left ventricular afterload; (2) this increased left ventricular asynchrony possibly contributes to the afterload dependent prolongation of left ventricular isovolumetric relaxation rate.

Neurosecretory cells in the honeybee brain and suboesophageal ganglion show FMRFamide-like immunoreactivity

Immunocytochemical analysis of the brain and suboesophageal ganglion of the honeybee Apis mellifera L. was combined with Lucifer Yellow backfilling from the corpora cardiaca and intracellular staining of single neurons. It is shown that more than one third of the cells that display FMRFamide-like immunoreactivity (F-LI) project to the corpora cardiaca, suggesting they are neurosecretory. Among the ca. 120 median neurosecretory cells (MNCs) in the pars intercerebralis about 32 show F-LI. The number of immunoreactive MNCs is highly variable and may depend on age and/or diet. Seven of at least 40 lateral neurosecretory cells display F-LI. They project through the brain via the medial branch of the bipartite nervus corporis cardiaci II. In the suboesophageal ganglion three types of immunoreactive neurosecretory cells were identified. Together with the median and the lateral neurosecretory cells in the brain these cells project through a single pair of nerves into the corpora cardiaca suggesting that the nervus corporis cardiaci (NCC) of the honeybee is a fusion of NCC I, II, and III described in other insects.

Inhibition of the M current in NG 108-15 neuroblastoma x glioma hybrid cells

The M current, IM, a voltage-dependent non-inactivating K current, was recorded in NG108-15 neuroblastoma x glioma hybrid cells, using the whole-cell mode of the patch-clamp technique. We studied inhibition of the M current by bradykinin, phorbol dibutyrate (PDBu), an activator of protein kinase C (PKC), and methylxanthines. Focal application of 0.1-5 microM bradykinin inhibited IM by about 60%; 5 nM bradykinin inhibited by about 40%. Bath application of 0.1 microM and 1 microM PDBu diminished IM to about half of the control value. Staurosporine, a PKC inhibitor, applied for 35-43 min in a concentration of 0.3 microM significantly reduced the effect of 1 microM PDBu. M current blockage by PDBu could be partly reversed by bath application of H-7 (51-64 microM), another PKC inhibitor. These observations suggest that the PDBu effect is really due to activation of PKC. The findings are compatible with the view [Brown DA, Higashida H (1988) J Physiol (Lond) 397:185-207] that the bradykinin effect on IM is mediated by PKC. However, three further observations suggest that this is only true for part of the bradykinin effect. When the suppression of IM by 1 microM PDBu was fully developed, 0.1 microM bradykinin produced a further inhibition of IM. Down-regulation of PKC by long-term treatment with PDBu reduced the effect of 0.1 microM bradykinin significantly but did not abolish it. Staurosporine (0.3 microM, applied for 31-46 min) failed to reduce the effect of 5 nM bradykinin significantly. The M current could be reversibly blocked by methylxanthines (caffeine, isobutyl-methylxanthine, theophylline) in the millimolar range, probably because of a direct action on the M channels.

Xamoterol recruits an inotropic reserve in the acutely failing, reperfused canine myocardium without detrimental effects on its subsequent recovery

The present study tested (1) whether xamoterol recruits an inotropic reserve in reperfused myocardium and (2) whether acute inotropic stimulation by xamoterol has deleterious consequences on the long-term recovery of the reperfused myocardium. Sixteen anaesthetized, open-chest dogs were bilaterally vagotomized and heart rate kept constant by left atrial pacing. The distal left circumflex coronary artery was occluded for 15 min and then reperfused for 8 h. The coronary occlusion resulted in regional myocardial dyskinesia and myocardial function remained severely depressed after release of the occlusion. At 10 min reperfusion, 8 dogs received xamoterol (100 micrograms/kg i.v.), whereas the remaining 8 dogs served as controls and received saline. Xamoterol increased mean systolic wall thickening velocity (from 1.47 +/- 2.34 (SD) mm/s at 10 min reperfusion to 7.13 +/- 3.55 mm/s at 30 min reperfusion and 7.64 +/- 2.48 mm/s at 1 h reperfusion, respectively, both P less than 0.05). In the control group, only a slow recovery of mean systolic wall thickening velocity was observed (from 3.14 +/- 3.30 mm/s to 2.96 +/- 3.74 mm/s and 4.03 +/- 3.00 mm/s at 10 min, 30 min, and 1 h reperfusion, respectively). At 8 h reperfusion, mean systolic wall thickening velocity was similar in both groups (7.97 +/- 4.23 mm/s in the xamoterol-group and 6.87 +/- 4.00 mm/s in the placebo-group). Histological examination revealed no difference in the extent of necrosis between the two groups after 8 h reperfusion. We conclude that (1) xamoterol recruits an inotropic reserve in reperfused myocardium, and (2) this recruitment of an inotropic reserve does not compromise functional recovery and structural integrity of the reperfused myocardium.

Recruitment of a time-dependent inotropic reserve by postextrasystolic potentiation in normal and reperfused myocardium

Impaired excitation-contraction coupling has been suggested as the underlying mechanism of postischemic contractile dysfunction of reperfused myocardium in in-vitro studies. To test this hypothesis in situ, postextrasystolic potentiation (PESP) following an extrasystole with constant prematurity and three different postextrasystolic time intervals (compensated, regular, abbreviated) was analyzed in 12 anesthetized dogs. Changes in regional inotropic state were assessed by comparison of end-systolic wall thickness (sonomicrometry) during PESP to the respective pressure-matched values of an end-systolic pressure/wall-thickness relationship established during brief manual clamping of the aorta. Before ischemia, posterior end-systolic wall-thickness was increased by 0.19 +/- 0.35 (SD) mm during PESP with an abbreviated, by 0.36 +/- 0.42 mm with a regular, and by 0.60 +/- 0.42 mm with a compensated postextrasystolic interval. Baseline systolic wall thickening was decreased from 16.2 +/- 5.4% (before ischemia) to -3.0 +/- 3.4% at the end of 15 min left circumflex coronary occlusion, and to 2.8 +/- 7.5% at 10 min, 7.2 +/- 3.9% at 4 h, and 7.9 +/- 4.1% at 8 h reperfusion. Stepwise increases in regional inotropic state during PESP with increasing postextrasystolic intervals were not different in normal and reperfused myocardium. Thus, excitation-contraction coupling appears not to be impaired during inotropic stimulation of reperfused myocardium in situ.

13C-NMR study of acetate assimilation in Thermoproteus neutrophilus

Acetate assimilation into amino acids and the functioning of central biosynthetic pathways in the extremely thermophilic anaerobic archaebacterium Thermoproteus neutrophilus was investigated using 13C NMR as the method for determination of the labelling patterns. Acetate was assimilated via reductive carboxylation of acetyl-CoA to pyruvate and pyruvate conversion to phosphoenolpyruvate which was further carboxylated to oxaloacetate. 2-Oxoglutarate was mainly formed via citrate. However, the labelling patterns of glutamic acid and alanine were in agreement with the concurrent synthesis of about 15% 2-oxoglutarate and 5% pyruvate through the reductive citric acid cycle. A scrambling phenomenon occurring in aspartate and all amino acids derived through oxaloacetate was observed. The labelling patterns of amino acids were in agreement with their standard biosynthetic pathways, with two remarkable exceptions: isoleucine was synthesized via the citramalate pathway and lysine was synthesized via the 2-aminoadipate pathway which has previously been reported only in eukaryotic microorganisms.

13C-NMR study of autotrophic CO2 fixation in Thermoproteus neutrophilus

The pathway of autotrophic CO2 fixation has been investigated in the extremely thermophilic sulfur-respiring anaerobic archaebacterium Thermoproteus neutrophilus. [1,4-13C2]Succinate was used as a tracer since this compound was incorporated in small amounts virtually into all cell compounds without affecting the organism's ability to synthesize all cell constituents from CO2. Three representative amino acids, glutamate, aspartate and alanine were isolated from cells after growth for several generations in the presence of [1,4-13C2]succinate and their labelling patterns were determined by 13C NMR spectroscopy. The data is consistent with CO2 fixation by a reductive citric acid cycle, as proposed earlier for the green sulfur bacterium Chlorobium limicola, the sulfate-reducing Desulfobacter hydrogenophilus and the microaerophilic Knallgasbacterium Hydrogenobacter thermophilus. The presence of a reductive citric acid cycle in archaebacteria indicates that this CO2 fixation mechanism which is an alternative to the Calvin cycle is present in many anaerobic or facultative anaerobic microorganisms.

Comparison of sulphated glycosaminoglycan and hyaluronate synthesis and secretion in cultured hepatocytes, fat storing cells, and Kupffer cells

The extracellular matrix of normal liver contains several types of proteoglycans including heparan sulphate, chondroitin sulphate isomers, dermatan sulphate, and the glycosaminoglycan, hyaluronic acid. In the present study both the synthesis and secretion as well as the pattern of radioactively labeled proteoglycans and hyaluronic acid of hepatocytes, fat-storing cells (Ito cells), and Kupffer cells maintained in monolayer cultures under mostly identical conditions were compared to assess their relative contribution to hepatic proteoglycan synthesis. Fat-storing cells were identified as the main type of cell producing and secreting proteoglycan and hyaluronic acid. More than 70% of labeled proteoglycan and hyaluronic acid were secreted into the medium. Heparan sulphate is the main type of proteoglycan in hepatocytes, whereas in the medium of fat-storing cells, chondroitin sulphate and dermatan sulphate comprise the major fractions. Hyaluronic acid was not detectable in hepatocyte cultures and found only in low amounts in the medium of Kupffer cells. The results point to a stringent quantitative and qualitative cellular compartmentation of proteoglycan synthesis in liver with fat-storing cells as the most important cell type for matrix proteoglycan and hyaluronic acid production.

Dopamine-like immunoreactivity in the brain and suboesophageal ganglion of the honeybee

The distribution of dopamine in the brain and suboesophageal ganglion of the honeybee Apis mellifera was investigated by means of immunocytochemistry with a well-characterized antiserum against dopamine. The binding of the antiserum in paraffin serial sections was studied with the peroxidase-antiperoxidase method. Dopamine-like immunoreactive neurons are present in most parts of the brain and in the suboesophageal ganglion. Only the optic lobes are devoid of label. There are ca. 330 dopamine immunoreactive somata in each brain hemisphere plus respective suboesophageal hemiganglion, which is less than 0.1% of the entire neuronal population. Most of the labelled somata are situated within three clusters: one below the lateral calyx and two in the anterior-ventral protocerebrum. Other labelled somata lie dispersed or in small groups around the protocerebral bridge, below the optic tubercles, proximal to the ventral rim of the lobula, and in the lateral and ventral somatal rind of the suboesophageal ganglion. Similar to neurons that react with an antiserum against serotonin, the fine processes of dopamine immunoreactive fibers have a varicose appearance which is typical for aminergic neurons. In addition to the neuronal staining, dopamine-like immunoreactivity is also present in the sheath surrounding the brain and in the retina, where it is not restricted to any particular cell type. A detailed account is given for those neurons and groups of neurons that could be traced and reconstructed in some detail. A common feature of all dopamine immunoreactive fibers is that each fiber invades large volumes of neuropil, suggesting that dopamine is more important in mediating distant rather than local neural interactions.

Phosphorylcholine acts as a Ca2+-dependent receptor molecule for lymphocyte perforin

Large granular lymphocytes and cytolytic T-lymphocytes (CTL) contain numerous cytoplasmic granules thought to be responsible, at least in part, for the cytolytic activity of these effector cells. Isolated granules are lytic for a variety of target cells and the granule proteins are specifically released upon target-cell interaction. Major proteins in mouse CTL granules are a family of seven serine proteases designated granzymes A to G, and a pore-forming protein called perforin (cytolysin). Purified perforin is cytolytic in the presence of Ca2+ and shows ultrastructural, immunological and amino-acid sequence similarities to complement component C9. Despite these similarities, perforin and C9 are clearly distinct in their mode of target-cell recognition. Whereas C9 insertion is absolutely dependent on a receptor moiety assembled from the complement proteins C5b, C6, C7, and C8 on the target-cell membrane, no requirement for a receptor molecule has been reported for perforin. Here, we demonstrate that phosphorylcholine acts as a specific, Ca2+-dependent receptor molecule for perforin.

Recruitment of inotropic reserve in "stunned" myocardium by the cardiotonic agent AR-L 57

Contractile dysfunction of reversibly injured, reperfused myocardium can be enhanced by inotropic interventions. A decrease in the Ca-sensitivity of contractile proteins with slow recovery during reperfusion has been suggested as a potential mechanism underlying this postischemic dysfunction. We therefore tested the effects of the cardiotonic agent AR-L 57 (1 mg/kg i.v.) in six anesthetized, vagotomized dogs during constant atrial pacing at 192 +/- 6 beats/min. Before ischemia, AR-L 57 increased left ventricular pressure from 131 +/- 22 to 138 +/- 21 mm Hg and maximum dP/dt from 3,022 +/- 1,427 to 4,337 +/- 2,608 mm Hg/s. Mean systolic thickening velocity of the posterior myocardium was increased from 8.9 +/- 1.1 to 11.7 +/- 1.1 mm/s. After release of a 15 min LCX-occlusion which caused complete regional akinesia, baseline function in the posterior myocardium was severely depressed and only gradually returned towards control values over 8 h of reperfusion. AR-L 57 increased systolic thickening velocity at 10 min, 4 and 8 h reperfusion to a similar extent as before ischemia. With reference to a purported Ca-sensitizing mechanism underlying the positive inotropic action of AR-L 57, our data suggest no change in the Ca-sensitivity of reperfused myocardium.

FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust (Schistocerca gregaria)

The distribution of FMRFamide-like immunoreactivity in the metathoracic ganglion of the locust, Schistocerca gregaria, has been investigated in serial semithin transverse sections with the use of the peroxidase-antiperoxidase (PAP) technique. The topographical distribution of approximately 120 immunopositive neurons was established. Antiserum against bovine pancreatic polypeptide (BPP) stains the same ganglionic cells as FMRFamide-antiserum, yet this staining is largely blocked after preabsorption to FMRFamide. A comparison of these results with those from other studies suggests that there may be more than one type of endogenous RFamide-like peptide.

Glutamate-like immunoreactivity in identified neuronal populations of insect nervous systems

Glutamate is considered to be the most likely transmitter candidate at excitatory synapses onto skeletal muscles of insects. We investigated the distribution of glutamate-like immunoreactivity (Glu-LI) in identified motor neurons of glutaraldehyde-fixed metathoracic ganglia of the locust in paraffin serial sections. The presumably glutamatergic fast and slow extensor tibiae motor neurons show Glu-LI, whereas other cells, including the GABAergic common inhibitory motor neurons and the cluster of octopaminergic dorsal unpaired median cells, show rather low levels of staining. Immunoreactivity of the fast extensor tibiae motor neuron is located in soma, neurites, axon, and the terminal arborizations. A double-labeling experiment on sections of the locust metathoracic ganglion showed that antisera against glutamate and GABA discriminate between the presumably glutamatergic and GABAergic motor neurons and that GABA-LI-positive neurons are low in Glu-LI. The results suggest that Glu-LI can be used as a marker for detecting potential glutamatergic neurons in insects under the present conditions. Application of the glutamate antiserum to sections of the honeybee brain revealed Glu-LI in motor neurons but also in certain interneurons. The most prominent populations of Glu-LI-positive cells were the monopolar cells and large ocellar interneurons, which are first-order interneurons of the visual and ocellar system. Several groups of descending interneurons also showed Glu-LI. The distributions of Glu-LI and GABA-LI are complementary in locust and bee ganglia. The high level of Glu-LI in certain interneuronal populations, as well as in identified glutamatergic motor neurons, suggests that insect central nervous systems may contain glutamatergic neuronal pathways.

The heparin binding domain of S-protein/vitronectin binds to complement components C7, C8, and C9 and perforin from cytolytic T-cells and inhibits their lytic activities

S-Protein/vitronectin is a serum glycoprotein that inhibits the lytic activity of the membrane attack complex of complement, i.e., of the complex including the proteins C5b, C6, C7, C8, and C9n. We show that intact S-protein/vitronectin or its cyanogen bromide generated fragments also inhibit the hemolysis mediated by perforin from cytotoxic T-cells at 45 and 11 microM, respectively. The glycosaminoglycan binding site of S-protein/vitronectin is responsible for the inhibition, since a synthetic peptide corresponding to a part of this highly basic domain (amino acid residues 348-360) inhibits complement- as well as perforin-mediated cytolysis. In the case of C9, the synthetic peptide binds to the acidic residues occurring in its N-terminal cysteine-rich domain (residues 101-111). Antibodies raised against this particular segment react 25-fold better with the polymerized form of C9 as compared with its monomeric form, indicating that this site becomes exposed only upon the hydrophilic-amphiphilic transition of C9. Since the cysteine-rich domain of C9 has been shown to be highly conserved in C6, C7, and C8 as well as in perforin, the inhibition of the lytic activities of these molecules by S-protein/vitronectin or by peptides corresponding to its heparin binding site may be explained by a similar mechanism.

Taurine-like immunoreactivity in the brain of the honeybee

Taurine (2-aminoethanesulfonic acid) is one of the most abundant free amino acids in the insect central nervous system. We have investigated the distribution of taurine-like immunoreactivity in the brain of the honeybee with an antiserum recognizing fixed taurine. Taurine-like immunoreactivity appeared within neuronal perikarya, neurites, and terminals, whereas glial cells were unlabelled. All photoreceptor cells of the compound eyes and the ocelli were stained. So were the fibers of the anterior superior optic tract, which connects the optic lobes to the mushroom bodies in the median protocerebrum. In the mushroom bodies the majority of intrinsic Kenyon cells showed high levels of taurine-like immunoreactivity. The lateral antennoglomerular tract, which interconnects the mushroom bodies with the antennal lobes, was also intensely stained. In the antennal lobes, strong labelling was observed within a few fibers that invade a set of posterior glomeruli from the posterior margin. Sensory projections from the antennal nerve into the antennal lobes showed only intermediate levels of staining. Sensory projections into the dorsal lobe were devoid of taurine-like immunoreactivity. Labral, mandibular, maxillary, and labial nerves, which innervate the various parts of the feeding apparatus, contain a set of five to eight heavily stained fibers. A comparison of taurine-like immunoreactivity with glutamate- and GABA-like immunoreactivities in the brain of the honeybee indicates that the three amino acids are enriched in distinct neuronal populations.

The synthesis of proteoglycans in fat-storing cells of rat liver

Fat-storing cells (perisinusoidal stellate cells) were isolated by enzymatic digestion of rat liver and purified by a single-step Nycodenz gradient to yield 11.4 X 10(6) cells per liver, with a purity of 74% and a viability of 76%. Monolayer cultures of fat-storing cells incorporated both [35S]sulfate and [3H]glucosamine into glycosaminoglycans; the rate of incorporation increased with culture time (3-fold between the third and eighth days in culture). About 80% of newly formed glycosaminoglycans were secreted into the medium. Analysis of the types of glycosaminoglycans revealed a different pattern for cells and medium, respectively, which is subject to culture time. Heparan sulfate remains primarily cell-bound and, therefore, has a low fractional secretion rate. Chondroitin sulfate and even more dermatan sulfate are the main types of glycosaminoglycans in the medium. Dermatan sulfate represents about 60% of total medium glycosaminoglycans. In advanced cultures (eighth day), this type becomes the predominant one in the cell layer. The reduction of the molecular weight of native medium-sulfated molecules by papain digestion and beta-elimination and the puromycin-induced inhibition of their synthesis by more than 75% suggest the formation of glycosaminoglycans as complex proteoglycans. It is concluded that fat-storing cells are a major cellular source of dermatan sulfate and chondroitin sulfate in liver connective tissue. Since the pattern of proteoglycans of fat-storing cells closely resembles that found in the fibrotic liver matrix, this cell type might be of pathogenetic significance for the accumulation of chondroitin sulfate and dermatan sulfate in cirrhotic connective tissue.

Inhibition of the lytic activity of perforin by lipoproteins

Cytoplasmic granules isolated from cytolytic T lymphocytes (CTL) lyse red blood cells or tumor cell lines in a nonspecific manner. The activity of highly purified granules was inhibited by human or rabbit serum at dilutions as high as 1/10,000. The main inhibitory activity of human serum was isolated by chromatography and was determined to be high density lipoprotein (HDL). HDL not only inhibited at a concentration of 70 ng/ml the lytic activity of isolated granules, but also of the purified, pore-forming protein perforin present in the granules. Purified low density lipoprotein was equally active. Because the CTL granule activity was inhibited by pure egg lecithin vesicles at a concentration equivalent to the phospholipid content of lipoproteins, the lipid portion of lipoproteins is the likely candidate for granule inactivation. Lipoproteins also decreased in a dose-dependent manner the cytotoxic activity of intact cytolytic T cells. However, cytotoxicity was not completely suppressed, and only in the case of CTL exhibiting low efficiency in killing their targets. It is proposed that lipoproteins inactivate perforin and may thereby inhibit a possible lysis of innocent bystander cells.

Inhibition of the lytic activity of perforin by lipoproteins

Cytoplasmic granules isolated from cytolytic T lymphocytes (CTL) lyse red blood cells or tumor cell lines in a nonspecific manner. The activity of highly purified granules was inhibited by human or rabbit serum at dilutions as high as 1/10,000. The main inhibitory activity of human serum was isolated by chromatography and was determined to be high density lipoprotein (HDL). HDL not only inhibited at a concentration of 70 ng/ml the lytic activity of isolated granules, but also of the purified, pore-forming protein perforin present in the granules. Purified low density lipoprotein was equally active. Because the CTL granule activity was inhibited by pure egg lecithin vesicles at a concentration equivalent to the phospholipid content of lipoproteins, the lipid portion of lipoproteins is the likely candidate for granule inactivation. Lipoproteins also decreased in a dose-dependent manner the cytotoxic activity of intact cytolytic T cells. However, cytotoxicity was not completely suppressed, and only in the case of CTL exhibiting low efficiency in killing their targets. It is proposed that lipoproteins inactivate perforin and may thereby inhibit a possible lysis of innocent bystander cells.

Common projection areas of 5-HT- and GABA-like immunoreactive fibers in the visual system of the honeybee

The visual system of the honeybee contains gamma-aminobutyric acid-(GABA)-like and 5-hydroxytryptamine-(5-HT)-like immunoreactive tangential fibers of similar morphology. These tangential fibers belong to two different cell types, as revealed by a double labelling procedure on the same section with GABA- and 5-HT-antisera, raised in different animals. The common projection areas of both fiber types suggests a possible interaction of serotonergic and GABAergic pathways in an insect visual system.

Distribution of GABA-like immunoreactivity in the brain of the honeybee

The distribution of GABA-like immunoreactivity in the brain of the honeybee was investigated with antisera generated against GABA protein conjugates. The binding of the antisera in paraffin serial sections was studied with the peroxidase-antiperoxidase method. GABA-like immunoreactive fibers appeared in all main neuropile areas. The staining of the optic lobes showed pronounced stratification. The receptor cells of compound eyes, ocelli, and antennae were not labelled. Several prominent fiber tracts showed GABA-like immunoreactivity, whereas other tracts were devoid of staining. There are no major immunoreactive commissures linking the two brain hemispheres with the exception of small commissures that bridge short distances between the beta-lobes and the antennal lobes. Several fibers in the cervical connective were also labelled; some of those may descend from the suboesophageal ganglion to the thoracic ganglia. The dense reactivity seen in the optic and antennal neuropiles implies that GABA is more important in mediating local rather than more distant neural interactions.

Increased hemolytic activity of the trypsin-cleaved ninth component of complement

Human C9 treated with trypsin is initially cleaved into two fragments with relative mol. wts of 53,000 and 20,000. This limited cleavage of C9 induces a 2.4-times increase in the hemolytic activity of C9 when compared to untreated C9. This difference diminishes when C9 activity is tested in an assay using a prolonged incubation time of C9 with C5b-8-bearing red blood cells. Trypsinization of C9 also promotes spontaneous C9 polymerization. SDS-resistant tubular C9 complexes are formed at a C9 concn of 1 mg/ml within 8 hr at 37 degrees C. Our data indicate that specific limited proteolysis of C9 not only induces spontaneous C9 polymerization but also increases the hemolytic activity of C9, suggesting that a similar molecular mechanism is involved in both processes.

Mushroom body feedback interneurones in the honeybee show GABA-like immunoreactivity

The distribution of the transmitter substance GABA was investigated in the mushroom body neuropile of the honeybee by means of immunohistochemistry. The protocerebro-calycal tract (PCT) links a mushroom body output area with the calycal input sites. Interneurones contained within the PCT exhibit GABA-like immunoreactivity and may function as negative feedback loop.

Nucleotide sequence of the dihydrofolate reductase gene of methotrexate-resistant Lactobacillus casei

The nucleotide sequence of the dihydrofolate reductase (DHFR) gene of a methotrexate-resistant strain of Lactobacillus casei, which is the source of DHFR for nuclear magnetic resonance (NMR) studies, has been determined. The derived amino acid sequence differs from that obtained by protein sequencing by the presence of aspartic acid instead of asparagine at position 8 and proline instead of leucine at position 90. The nucleotide sequences of 320-bp 5' and 335-bp 3' flanking regions of this gene have also been determined.

On the absorption of divalent and trivalent iron in living rats

For therapeutic purposes ferric and ferrous iron seems to be evaluated in favour of the latter, despite of the fact that at least in animal experiments no difference was observed as far as the bioavailability of either valency state of iron is concerned; prerequisite is that iron has been administered in ionized form. These results have been proven actually by the studies on normal and iron-deficient rats in vivo fed by stomach tube with radioactively labeled 59Fe-(FeSO4), 59Fe-(FeCl3), and the organic complex of 59Fe-Fe(III)-polymaltose). At least in iron-deficient rats the utilization of iron administered in the form of the organic complex was little less than that obtained after having fed FeSO4. Besides the retention of 59Fe-radioactivity 6 days later after the administration also the uptake of 59Fe-radioactivity into erythrocytes and liver has been measured.

Classical conditioning of proboscis extension in honeybees (Apis mellifera)

Extension of the proboscis was conditioned in restrained honeybees with odor as the conditioned stimulus (CS) and sucrose solution--delivered to the antenna (to elicit extension of the proboscis) and then to the proboscis itself--as the unconditioned stimulus (US). In a first series of experiments, acquisition was found to be very rapid, both in massed and in spaced trials; its associative basis was established by differential conditioning and by an explicitly unpaired control procedure (which produced marked resistance to acquisition in subsequent paired training); and both extinction and spontaneous recovery in massed trials were demonstrated. In a series of experiments on the nature of the US, eliminating the proboscis component was found to lower the asymptotic level of performance, whereas eliminating the antennal component was without effect; reducing the concentration of sucrose from 20% to 7% slowed acquisition but did not lower the asymptotic level of performance; and second-order conditioning was demonstrated. In a series of experiments on the role of the US, an omission contingency designed to eliminate adventitious response-reinforcer contiguity was found to have no adverse effect on acquisition. In a series of experiments designed to analyze the resistance to acquisition found after explicitly unpaired training in the first experiments, no significant effect was found of prior exposure either to the CS alone or to the US alone, although the unpaired procedure again produced substantial resistance that was shown to be due to inhibition rather than to inattention; extinction after paired training was found to be facilitated by unpaired presentations of the US. The relation between these results for honeybees and those of analogous experiments with vertebrates is considered.

Influence of fucoidan on the intestinal absorption of iron, cobalt, manganese and zinc in rats

Fucoidan was extracted from the seaweed Ascophyllum nodosum with boiling water and purified by repeated precipitation steps. Increasing doses of fucoidan (1.2--200 mg) were injected together with 360 nmol 59Fe-(FeCl3) or 60Co-(CoCl2) into tied-off jejunal segments of two groups of rats fed either a normal (160 mg Fe/kg) or a low iron diet (5 mg/kg). Fucoidan together with 360 nmol 54Mn-(MnCl2) or 65Zn-(ZnCl2) was administered in the same manner in rats fed a normal diet only. Fucoidan administered in doses above 30 mg decreased the absorption of iron, cobalt, manganese and zinc in normal rats, and the absorption of iron and cobalt in iron-deficient rats. This inhibitory effect of fucoidan on the absorption of heavy metals is apparently the consequence of the formation of metal complexes which are poorly absorbed from the intestinal lumen.