Layer-specific distribution and expression pattern of AMPA- and NMDA-type glutamate receptors in the barrel field of the adult rat somatosensory cortex: a quantitative electron microscopic analysis

AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-d-aspartate) glutamate receptors are driving forces for synaptic transmission and plasticity at neocortical synapses. However, their distribution pattern in the adult rat neocortex is largely unknown and was quantified using freeze fracture replication combined with postimmunogold-labeling. Both receptors were co-localized at layer (L)4 and L5 postsynaptic densities (PSDs). At L4 dendritic shaft and spine PSDs, the number of gold grains detecting AMPA was similar, whereas at L5 shaft PSDs AMPA-receptors outnumbered those on spine PSDs. Their number was significantly higher at L5 vs. L4 PSDs. At L4 and L5 dendritic shaft PSDs, the number of gold grains detecting GluN1 was ~2-fold higher than at spine PSDs. The number of gold grains detecting the GluN1-subunit was higher for both shaft and spine PSDs in L5 vs. L4. Both receptors showed a large variability in L4 and L5. A high correlation between the number of gold grains and PSD size for both receptors and targets was observed. Both receptors were distributed over the entire PSD but showed a layer- and target-specific distribution pattern. The layer- and target-specific distribution of AMPA and GluN1 glutamate receptors partially contribute to the observed functional differences in synaptic transmission and plasticity in the neocortex.

Translationally controlled tumour protein (TCTP) is a novel glucose-regulated protein that is important for survival of pancreatic beta cells

AIMS/HYPOTHESIS

This study used proteomics and biochemical approaches to identify novel glucose-regulated proteins and to unveil their role in pancreatic beta cell function. Translationally controlled tumour protein (TCTP) was identified to be one such protein, and further investigations into its function and regulation were carried out.

METHODS

Global protein profiling of beta cell homogenates following glucose stimulation was performed using two-dimensional gel electrophoresis. Proteins were identified by mass spectroscopy analysis. Immunoblotting was used to investigate alterations in TCTP protein levels in response to glucose stimulation or cell stress induced by palmitate. To investigate the biological function of TCTP, immunolocalisation, gene knockdown and overexpression of Tctp (also known as Tpt1) were performed. Apoptosis was measured in Tctp knockdown or Tctp-overexpressing cells. Glucose-stimulated insulin secretion was carried out in Tctp knockdown cells.

RESULTS

TCTP was identified as a novel glucose-regulated protein, the level of which is increased at stimulatory glucose concentration. Glucose also induced TCTP dephosphorylation and its partial translocation to the mitochondria and the nucleus. TCTP protein levels were downregulated in response to cell stress induced by palmitate or thapsigargin treatments. Gene knockdown by small interfering RNA led to increased apoptosis, whereas overproduction of TCTP prevented palmitate-induced cell death.

CONCLUSIONS/INTERPRETATION

Regulation of TCTP protein levels by glucose is likely to be an important cyto-protective mechanism for pancreatic beta cells against damage caused by hyperglycaemia. In contrast, high concentration of palmitate causes cell stress, reduction in TCTP levels and consequently reduced cell viability. Our results imply that TCTP levels influence the sensitivity of beta cells to apoptosis.

ATG16L1 and IL23 receptor (IL23R) genes are associated with disease susceptibility in Hungarian CD patients

BACKGROUND

North American and European genome-wide association scans have identified ATG16L1 and IL23R as novel inflammatory bowel disease (IBD) susceptibility genes and subsequent reports confirmed these findings in large independent populations. The aims of this study were to investigate the association and examine genotype-phenotype relationships in a Hungarian IBD cohort.

METHODS

415 unrelated IBD patients (CD: 266, age: 35.2+/-12.1 years, duration: 8.7+/-7.5 years and UC: 149, age: 44.4+/-15.4 years, duration: 10.7+/-8.9 years) and 149 healthy subjects were investigated. IL23R Arg381Gln (R381Q, rs11209026) and ATG16L1 Thr300Ala (T300A, rs2241880) polymorphisms were tested using LightCycler allele discrimination method. Detailed clinical phenotypes were determined by reviewing the medical charts.

RESULTS

The association between IL23R rs11209026, ATG16L1 rs2241880 and CD was confirmed (OR(IL23R381Q): 0.38, 95% CI: 0.16-0.87; OR(ATG16L1300AA): 1.86, 95% CI: 1.04-3.40). No difference was found between patients with UC and either controls or CD. In CD, IL23R 381Gln heterozygosity was associated with inflammatory disease (70% vs. 34%, p=0.037), while disease restricted to the colon was more prevalent in patients with the ATG16L1 300Ala/Ala homozygosity (33.3% vs. 21.1%, p=0.036). In addition, carriage of the variant alleles did not predict response to steroids, infliximab or need for surgery.

CONCLUSIONS

We confirmed that ATG16L1 and IL23R are susceptibility loci for CD in Hungarian CD patients. Further studies are needed to confirm the reported phenotype-genotype associations found in this study.

Pathological and immunological studies on goose embryos and one-day-old goslings experimentally infected with a Mycoplasma strain of goose origin

Goose embryos and one-day-old goslings were inoculated either on the 10th or 20th day of incubation into the yolk sac or into the air sac or intranasally, with Mycoplasma strain 1220 isolated from a goose. Subsequently morphological, immunological and microbiological * changes were determined. Infection during incubation resulted in an acute serous inflammation of the chorioallantoic membrane, a diffuse, heterophil granulocytic interstitial hepatitis and a bronchopneumonia. One-day-old goslings developed lympho-histiocytic infiltrations of the productive type in the interstitium of the lungs, the walls of the major bronchi, the mucous membrane of the nasal conchae and in the visceral pleura. Blood lymphocytes of 28-day-old embryos infected at 10 days of incubation recognised and specifically reacted with the antigen in immunorosette formation and lymphocyte transformation tests. However, after hatching the antigen-recognising capacity of lymphocytes decreased, and had become considerably reduced by day 30 after hatching. No antibodies were demonstrable in the indirect haemagglutination test.

A CaV2.1 calcium channel mutationrockerreduces the number of postsynaptic AMPA receptors in parallel fiber-Purkinje cell synapses

The rocker mice are hereditary ataxic mutants that carry a point mutation in the gene encoding the CaV2.1 (P/Q-type) Ca2+ channel alpha1 subunit, and show the mildest symptoms among the reported CaV2.1 mutant mice. We studied the basic characteristics of the rocker mutant Ca2+ channel and their impacts on excitatory synaptic transmission in cerebellar Purkinje cells (PCs). In acutely dissociated PC somas, the rocker mutant channel showed a moderate reduction in Ca2+ channel current density, whereas its kinetics and voltage dependency of gating remained nearly normal. Despite the small changes in channel function, synaptic transmission in the parallel fiber (PF)-PC synapses was severely impaired. The climbing fiber inputs onto PCs showed a moderate impairment but could elicit normal complex spikes. Presynaptic function of the PF-PC synapses, however, was unexpectedly almost normal in terms of paired-pulse facilitation, sensitivity to extracellular Ca2+ concentration and glutamate concentration in synaptic clefts. Electron microscopic analyses including freeze-fracture replica labeling revealed that both the number and density of postsynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors substantially decreased without gross structural changes of the PF-PC synapses. We also observed an abnormal arborization of PC dendrites in young adult rocker mice (approximately 1 month old). These lines of evidence suggest that even a moderate dysfunction of CaV2.1 Ca2+ channel can cause substantial changes in postsynaptic molecular composition of the PF-PC synapses and dendritic structure of PCs.

Concomitant deficits in working memory and fear extinction are functionally dissociated from reduced anxiety in metabotropic glutamate receptor 7-deficient mice

Metabotropic glutamate receptor 7 (mGluR7), a receptor with a distinct brain distribution and a putative role in anxiety, emotional responding, and spatial working memory, could be an interesting therapeutic target for fear and anxiety disorders. mGluR7-deficient (mGluR7-/-) mice showed essentially normal performance in tests for neuromotor and exploratory activity and passive avoidance learning but prominent anxiolytic behavior in two anxiety tests. They showed a delayed learning curve during the acquisition of the hidden-platform water maze, and three interspersed probe trials indicated that mGluR7-/- mice were slower to acquire spatial information. Working memory in the water maze task and the radial arm maze was impaired in mGluR7-/- mice compared with mGluR7+/+. mGluR7-/- mice also displayed a higher resistance to extinction of fear-elicited response suppression in a conditioned emotional response protocol. In a non-fear-based water maze protocol, mGluR7-/- mice displayed similar delayed extinction. These observed behavioral changes are probably not attributable to changes in AMPA or NMDA receptor function because expression levels of AMPA and NMDA receptors were unaltered. Extinction of conditioned fear is an active and context-dependent form of inhibitory learning and an experimental model for therapeutic fear reduction. It appears to depend on glutamatergic and higher-level brain functions similar to those involved in spatial working memory but functionally dissociated from those that mediate constitutional responses in anxiety tests.

Tyrosine phosphatases regulate AMPA receptor trafficking during metabotropic glutamate receptor-mediated long-term depression

Two forms of long-term depression (LTD), triggered by activation of NMDA receptors (NMDARs) and metabotropic glutamate receptors (mGluRs), respectively, can be induced at CA1 synapses in the hippocampus. Compared with NMDAR-LTD, relatively little is known about mGluR-LTD. Here, we show that protein tyrosine phosphatase (PTP) inhibitors, orthovanadate and phenylarsine oxide, selectively block mGluR-LTD induced by application of the group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG-LTD), because NMDAR-LTD is unaffected by these inhibitors. Furthermore, DHPG-LTD measured using whole-cell recording is similarly blocked by either bath-applied or patch-loaded PTP inhibitors. These inhibitors also block the changes in paired-pulse facilitation and coefficient of variation that are associated with the expression of DHPG-LTD. DHPG treatment of hippocampal slices was associated with a decrease in the level of tyrosine phosphorylation of GluR2 AMPA receptor (AMPAR) subunits, an effect blocked by orthovanadate. Finally, in dissociated hippocampal neurons, orthovanadate blocked the ability of DHPG to reduce the number of AMPA receptor clusters on the surface of dendrites. Again, the effects of PTP blockade were selective, because NMDA-induced decreases in surface AMPAR clusters was unaffected by orthovanadate. Together, these data suggest that activation of postsynaptic PTP results in tyrosine dephosphorylation of AMPARs and their removal from the synapse.

Experience-dependent modification of mechanisms of long-term depression

Mechanisms of long-term potentiation and depression (LTP and LTD) change considerably during development, but the importance of these changes and the factors that control them is not clear. We found that visual experience triggered a switch in mechanisms of LTD in rat perirhinal cortex, an area critical for visual recognition memory. Thus, changes in synaptic plasticity mechanisms were correlated with the changing physiological demands on the CNS.

Number and density of AMPA receptors in single synapses in immature cerebellum

The number of ionotropic receptors in synapses is an essential factor for determining the efficacy of fast transmission. We estimated the number of functional AMPA receptors at single postsynaptic sites by a combination of two-photon uncaging of glutamate and the nonstationary fluctuation analysis in immature rat Purkinje cells (PCs), which receive a single type of excitatory input from climbing fibers. Areas of postsynaptic membrane specialization at the recorded synapses were measured by reconstruction of serial ultrathin sections. The number of functional AMPA receptors was proportional to the synaptic area with a density of approximately 1280 receptors/microm2. Moreover, highly sensitive freeze-fracture replica labeling revealed a homogeneous density of immunogold particles for AMPA receptors in synaptic sites (910 +/- 36 particles/microm2) and much lower density in extrasynaptic sites (19 +/- 2 particles/microm2) in the immature PCs. Our results indicate that in this developing synapse, the efficacy of transmission is determined by the synaptic area.

Differential roles of NR2A and NR2B-containing NMDA receptors in cortical long-term potentiation and long-term depression

It is widely believed that long-term depression (LTD) and its counterpart, long-term potentiation (LTP), involve mechanisms that are crucial for learning and memory. However, LTD is difficult to induce in adult cortex for reasons that are not known. Here we show that LTD can be readily induced in adult cortex by the activation of NMDA receptors (NMDARs), after inhibition of glutamate uptake. Interestingly there is no need to activate synaptic NMDARs to induce this LTD, suggesting that LTD is triggered primarily by extrasynaptic NMDA receptors. We also find that de novo LTD requires the activation of NR2B-containing NMDAR, whereas LTP requires activation of NR2A-containing NMDARs. Surprisingly another form of LTD, depotentiation, requires activation of NR2A-containing NMDARs. Therefore, NMDARs with different synaptic locations and subunit compositions are involved in various forms of synaptic plasticity in adult cortex.

Activation of metabotropic glutamate receptors does not alter the phosphorylation state of GluR1 AMPA receptor subunit at serine 845 in perirhinal cortical neurons

Activation of group I and group II metabotropic glutamate receptors (mGluRs) is thought to be required for long-term depression (LTD) of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor-mediated synaptic transmission in the perirhinal cortex. However, little is known about how activation of mGluRs leads to this form of synaptic plasticity. AMPA receptor phosphorylation has been implicated in several forms of modulation of synaptic transmission. In the CA1 area of the hippocampus, N-methyl-d-aspartate (NMDA) receptor-dependent LTD is associated with the reduced phosphorylation of the GluR1 AMPA receptor subunit at serine 845 (GluR1-S845). Immunoblot analysis of perirhinal cortical neurons using GluR1 and GluR1-S845 phosphorylation state specific antibodies showed that stimulation of adenylyl cyclase (AC) with forskolin (FSK) dramatically increased PKA-mediated phosphorylation of GluR1-S845. However, selective or simultaneous application of mGluR5 agonist (S)-3,5-dihydroxyphenylglycine (CHPG) and mGluR2/3 agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG IV) did not produce detectable changes in GluR1-S845 phosphorylation. These results indicate that in the perirhinal cortex mGluR activation does not alter the phosphorylation state of GluR1-S845. Therefore, it is likely that the process involved in the modification of AMPA receptors in mGluR activation dependent LTD in the perirhinal cortex is mechanistically distinct from NMDA receptor-mediated LTD described in hippocampal neurons.

Metabotropic glutamate receptors are expressed in adult human glial progenitor cells

Glial precursor cells (GPCs) are present in the adult human central nervous system (CNS) and they can be isolated and maintained in culture for in vitro studies. This study analysed expression of mGluR3 and mGluR5 metabotropic glutamate receptor (mGluR) mRNAs in GPCs. A2B5 surface antigen positive GPCs were isolated using immunomagnetic selection from dissociated temporal lobe subcortical white matter cells. The separated GPCs were maintained in cultures and characterised by immunoreactivity for the differentiation markers A2B5 and human platelet-derived growth factor-alpha receptor (PDGFalphaR). Reverse transcription followed by multiplex PCR analysis showed that the GPCs expressed both mGluR3 and mGluR5a mRNAs. Double immunostaining for glial progenitor markers and mGluR5 proteins demonstrated that all A2B5 and PDGFalphaR-positive cells were also positive for mGluR5. The results indicate that GPCs present in the adult human CNS express mGluR3 and mGluR5a. These neurotransmitter receptors may be involved in the proliferation and differentiation of glial cells.

Metabotropic glutamate receptor signalling in perirhinal cortical neurons

Long-term depression (LTD) induction relies upon receptor cross-talk between group I and group II metabotropic glutamate receptors (mGluRs) in perirhinal cortex. The molecular mechanism of this mGluR interplay is not clear. Here, we show that the mGluR subtypes postulated to be involved in this mechanism are developmentally regulated and mGluR2 has a preferential role over mGluR3 in the synergistic interaction with mGluR5. We have identified a >70% reduction in basal cAMP levels following mGluR2 stimulation, which could lead to increased mGluR5 function via reduced PKA mediated phosphorylation and decreased desensitisation of mGluR5. To further investigate the roles of mGluRs in downstream intracellular signalling, we have examined the effects of mGluRs on the phosphorylation state of cAMP response element-binding protein (CREB). Both group I and group II agonists increased the phosphorylation of CREB, which indicates a cAMP- and PKA-independent signalling mechanism. These results suggest a convergence of signalling mechanisms from surface mGluRs to CREB-mediated transcription.

Assembly and cell surface expression of KA-2 subunit-containing kainate receptors

Kainate receptors (KARs) modulate synaptic transmission at both pre-synaptic and post-synaptic sites. The overlap in the distribution of KA-2 and GluR6/7 subunits in several brain regions suggests the co-assembly of these subunits in native KARs. The molecular mechanisms that control the assembly and surface expression of KARs are unknown. Unlike GluR5-7, the KA-2 subunit is unable to form functional homomeric KAR channels. We expressed the KA-2 subunit alone or in combination with other KAR subunits in HEK-293 cells. The cell surface expression of the KAR subunit homo- and heteromers were analysed using biotinylation and agonist-stimulated cobalt uptake. While GluR6 or GluR7 homomers were expressed on the cell surface, KA-2 alone was retained within the endoplasmic reticulum. We found that the cell surface expression of KA-2 was dramatically increased by co-expression with either of the low-affinity KAR subunits GluR5-7. However, co-expression with other related ionotropic glutamate receptor subunits (GluR1 and NR1) does not facilitate the cell surface expression of KA-2. The analysis of subcellular fractions of neocortex revealed that synaptic KARs have a relatively high KA-2 content compared to microsomal ones. Thus, KA-2 is likely to contain an endoplasmic reticulum retention signal that is shielded on assembly with other KAR subunits.

Functional metabotropic glutamate receptors are expressed in oligodendrocyte progenitor cells

We investigated the expression of metabotropic glutamate receptor (mGluR) isoforms in CG-4 rodent oligodendroglial progenitor cells (OPC) and rat brain oligodendrocytes. Our RT-PCR analysis detected mRNAs for mGluR3 and mGluR5 isoforms in OPCs. Although neurons express both mGluR5a and mGluR5b splice variants, only mGluR5a was identified in OPCs. Antibodies to mGluR2/3 and mGluR5 detected the corresponding receptor proteins in immunoblots of OPC membrane fractions. Furthermore, immunocytochemical analysis identified mGluR5 in oligodendrocyte marker O4-positive OPCs. The expression of mGluR5 was also demonstrated in oligodendrocyte marker (O4 and O1) positive cells in white matter of postnatal 4- and 7-day-old rat brain sections using immunofluorescent double labelling and confocal microscopy. The mGluR5 receptor function was assessed in CG-4 OPCs with fura-2 microfluorometry. Application of the mGluR1/5 specific agonist (S)-3,5-dihydroxyphenylglycine (DHPG) induced calcium oscillations, which were inhibited by the selective mGluR5 antagonist 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). The DHPG induced calcium oscillations required Ca2+ release from intracellular stores. In OPCs the group II mGluR agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) decreased forskolin-stimulated cAMP synthesis, indicating the presence of functional mGluR3. The newly identified mGluR3 and mGluR5a may be involved in the differentiation of oligodendrocytes, myelination and the development of white matter damage.

Activity blockade increases the number of functional synapses in the hippocampus of newborn rats

During development neuronal circuitries are refined by activity. Here we studied the role of spontaneous electrical activity in the regulation of synapse formation in the intact newborn (Postnatal Day 3; P3) rat hippocampus in vitro. The blockade of the spontaneous network activity with TTX led to an increase in the number of functional excitatory synapses in the CA3 area of the developing hippocampus. In parallel, there was a substantial increase in the expression levels of the presynaptic markers synaptophysin, synaptotagmin, and synapsin I and of GluR1 AMPA receptor subunits. These changes were associated with an increase in the frequency and amplitude of AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs). Our correlated immunocytochemical, electronmicroscopical, and electrophysiological experiments indicate that in the developing hippocampus spontaneous network activity controls the number of functional synapses.

Developmental changes in ionotropic glutamate receptors: lessons from hippocampal synapses

Glutamatergic synapses are the primary source of excitatory transmission in the central nervous system (CNS), and their formation is critical in the establishment of neuronal connections. The refinement of these connections occurs during development and also it is postulated during learning and memory. Recent progress in understanding the molecular components of synaptic junctions, together with advances in imaging techniques, has started to offer new insights into the development of excitatory synapses. Studies performed on low-density primary neuronal cultures have enabled dissection of the temporal sequence of events, which have lead to the differentiation of pre- and postsynaptic components. A central feature of the development of excitatory synapses is the accumulation of glutamatergic receptors (GluRs) at the postsynaptic site. These receptors need to be localized and fixed opposite nerve terminals that release glutamate. But for this to occur, neurons require intracellular anchoring molecules, as well as mechanisms that ensure the efficient turnover and transport of receptor proteins. This review focuses on some of the developmental changes observed in the subcellular distribution and molecular organization of AMPA and NMDA type ionotropic GluRs (iGluRs), which mediate the majority of fast excitatory neurotransmission in the CNS.

Metabotropic glutamate and GABA(B) receptors contribute to the modulation of glucose-stimulated insulin secretion in pancreatic beta cells

AIMS/HYPOTHESIS

The neurotransmitters glutamate and gamma-aminobutyric acid (GABA) could participate in the regulation of the endocrine functions of islets of Langerhans. We investigated the role of the metabotropic glutamate (mGluRs) and GABA(B) (GABA(B)Rs) receptors in this process.

METHODS

We studied the expression of mGluRs and GABA(B)Rs in rat and human islets of Langerhans and in pancreatic alpha-cell and beta-cell lines using RT-PCR and immunoblot analysis. Effects of mGluR and GABA(B) R agonists on insulin secretion were determined by radioimmunoassays and enzyme-linked immunoadsorbent assays (ELISAs).

RESULTS

We detected mGluR3 and mGluR5 (but not mGluR1, 6 and 7) mRNAs in all of the samples examined. Trace amount of mGluR2 was found in MIN6 beta cells; mGluR4 was identified in rat islets; and mGluR8 expression was detected in rat islets, RINm5F and MIN6 cells. GABA(B)R1 a/b and 2 mRNAs were identified in islets of Langerhans and MIN6 cells. The expression of mGluR3, mGluR5, GABA(B)R1 a/b and GABA(B)R2 proteins was confirmed using specific antibodies. Group I (mGluR1/5) and group II (mGluR2/3) specific mGluR agonists increased the release of insulin in the presence of 3 to 10 mmol/l or 3 to 25 mmol/l glucose, respectively, whereas a group III (mGluR4/6-8) specific agonist inhibited insulin release at high (10-25 mmol/l) glucose concentrations. Baclofen, a GABA(B)R agonist, also inhibited the release of insulin but only in the presence of 25 mmol/l glucose.

CONCLUSION/INTERPRETATION

These data suggest that mGluRs and GABA(B)Rs play a role in the regulation of the endocrine pancreas with mechanisms probably involving direct activation or inhibition of voltage dependent Ca(2+)-channels, cAMP generation and G-protein-mediated modulation of K(ATP) channels.

Developmental and activity dependent regulation of ionotropic glutamate receptors at synapses

Glutamate receptors mediate the majority of excitatory responses in the central nervous system. The establishment and refinement of glutamatergic synaptic connections depend on the concerted actions of alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA), N-methyl-D-aspartate (NMDA), and kainate (KA) type ionotropic glutamate receptors (iGluRs) and G-protein coupled metabotropic receptors. While a lot remains to be clarified, the most is known about the mechanisms by which the iGluR subtypes are targeted and how this is influenced by synaptic activity on both short and long time scales. Changes in their subunit compositions are also input specific and developmentally regulated. The identification of key molecular components of the postsynaptic density (PSD) and novel proteins that influence receptor targeting and clustering have started to reveal the underlying molecular mechanisms of the trafficking and targeting of iGluRs. Here we discuss the evidence that these basic mechanisms are used during developmental synaptic plasticity.

Transient synaptic activation of NMDA receptors leads to the insertion of native AMPA receptors at hippocampal neuronal plasma membranes

The molecular mechanisms underlying long-term potentiation (LTP) of excitatory synaptic transmission in the hippocampus are not well understood. Transient depolarisation of cultured postnatal hippocampal neurones (3x1 s exposure to 90 mM K+) induces a form of LTP that is manifest primarily as an increase in mEPSC frequency. Site-directed antibodies that recognise an extracellular region of all AMPA receptor (AMPAR) subunits (GluR1-4) were used for the immunolabelling of living neurones. These antibodies were raised in two species to enable sequential immunofluorescent labelling of individual living neurones before and after the induction of LTP. High K+ treatment resulted in the appearance of new AMPAR clusters at sites on the neuronal surface that previously lacked detectable AMPARs. The appearance of new AMPAR clusters was NMDA receptor (NMDAR)-dependent since it was antagonised by the application of NMDAR antagonists. Our data indicate that the transient synaptic activation of NMDARs can lead to the insertion of native AMPARs at sites on the neuronal membrane that initially lacks AMPARs.

An electrophysiological characterisation of long-term potentiation in cultured dissociated hippocampal neurones

Long-term potentiation (LTP) of synaptic transmission is under intense investigation. It is believed that the mechanisms involved in its induction and expression are critically involved in synaptic processes that are important for learning and memory and other physiological functions. A reliable means of inducing LTP in dissociated cultured neurones would facilitate investigations into the molecular basis of LTP but has been hard to achieve. Here we report a mechanism for inducing LTP in postnatal dissociated hippocampal neurones using transient depolarisation. This form of LTP is prevented by NMDA receptor antagonists and by chelating Ca2+ in the postsynaptic neurone. It is manifest primarily as an increase in the frequency of mEPSCs.

GABA(B) receptors couple directly to the transcription factor ATF4

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA), acts at ionotropic (GABA(A) and GABA(C)) and metabotropic (GABA(B)) receptors. Functional GABA(B) receptors are heterodimers of GABA(B(1)) and GABA(B(2)) subunits. Here we show a robust, direct, and specific interaction between the coiled-coil domain present in the C-terminus of the GABA(B(1)) subunit and the transcription factor ATF4 (also known as CREB2). ATF4 and GABA(B(2)) binding to the GABA(B(1)) subunit were mutually exclusive. In rat hippocampal neurons native GABA(B(1)) showed surprisingly little similarity to GABA(B(2)) in its subcellular distribution. GABA(B(1)) and ATF4, however, were highly colocalized throughout the cell and displayed a punctate distribution within the dendrites. Activation of GABA(B) receptors in hippocampal neurons caused a dramatic translocation of ATF4 out of the nucleus into the cytoplasm. These data suggest a novel neuronal signaling pathway that could regulate the functional expression of GABA(B) receptors and/or modulate gene transcription.

Developmental changes in synaptic AMPA and NMDA receptor distribution and AMPA receptor subunit composition in living hippocampal neurons

AMPA and NMDA receptors mediate most excitatory synaptic transmission in the CNS. We have developed antibodies that recognize all AMPA or all NMDA receptor variants on the surface of living neurons. AMPA receptor variants were identified with a polyclonal antibody recognizing the conserved extracellular loop region of all four AMPA receptor subunits (GluR1-4, both flip and flop), whereas NMDA receptors were immunolabeled with a polyclonal antibody that binds to an extracellular N-terminal epitope of the NR1 subunit, common to all splice variants. In non-fixed brain sections these antibodies gave labeling patterns similar to autoradiographic distributions with particularly high levels in the hippocampus. Using these antibodies, in conjunction with GluR2-specific and synaptophysin antibodies, we have directly localized and quantified surface-expressed native AMPA and NMDA receptors on cultured living hippocampal neurons during development. Using a quantitative cell ELISA, a dramatic increase was observed in the surface expression of AMPA receptors, but not NMDA receptors, between 3 and 10 d in culture. Immunocytochemical analysis of hippocampal neurons between 3 and 20 d in vitro shows no change in the proportion of synapses expressing NMDA receptors (approximately 60%) but a dramatic increase (approximately 50%) in the proportion of them that also express AMPA receptors. Furthermore, over this period the proportion of AMPA receptor-positive synapses expressing the GluR2 subunit increased from approximately 67 to approximately 96%. These changes will dramatically alter the functional properties of hippocampal synapses.

Alpha4 but not alpha3 and alpha7 nicotinic acetylcholine receptor subunits are lost from the temporal cortex in Alzheimer's disease

Neuronal nicotinic acetylcholine receptors labelled with tritiated agonists are reduced in the cerebral cortex in Alzheimer's disease (AD), but to date it has not been demonstrated which nicotinic receptor subunits contribute to this deficit. In the present study, autopsy tissue from the temporal cortex of 14 AD cases and 15 age-matched control subjects was compared using immunoblotting with antibodies against recombinant peptides specific for alpha3, alpha4, and alpha7 subunits, in conjunction with [3H]epibatidine binding. Antibodies to alpha3, alpha4, and alpha7 produced one major band on western blots at 59, 51, and 57 kDa, respectively. [3H]Epibatidine binding and alpha4-like immunoreactivity (using antibodies against the extracellular domain and cytoplasmic loop of the alpha4 subunit) were reduced in AD cases compared with control subjects (p < 0.02) and with a subgroup of control subjects (n = 9) who did not smoke prior to death (p < 0.05) for the former two parameters. [3H]Epibatidine binding and cytoplasmic alpha4-like immunoreactivity were significantly elevated in a subgroup of control subjects (n = 4) known to have smoked prior to death (p < 0.05). There were no significant changes in alpha3- or alpha7-like immunoreactivity associated with AD or tobacco use. The selective involvement of alpha4 has implications for understanding the role of nicotinic receptors in AD and potential therapeutic targets.

Surface expression of AMPA receptors in hippocampal neurons is regulated by an NSF-dependent mechanism

Here, we show that disruption of N-ethylmaleimide-sensitive fusion protein- (NSF-) GluR2 interaction by infusion into cultured hippocampal neurons of a blocking peptide (pep2m) caused a rapid decrease in the frequency but no change in the amplitude of AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs). N-methyl-D-aspartate (NMDA) receptor-mediated mEPSCs were not changed. Viral expression of pep2m reduced the surface expression of alpha-amino-3-hydroxy-5-methyl-isoxazolepropionate (AMPA) receptors, whereas NMDA receptor surface expression in the same living cells was unchanged. In permeabilized neurons, the total amount of GluR2 immunoreactivity was unchanged, and a punctate distribution of GluR2 was observed throughout the dendritic tree. These data suggest that the NSF-GluR2 interaction is required for the surface expression of GluR2-containing AMPA receptors and that disruption of the interaction leads to the functional elimination of AMPA receptors at synapses.

[Hormonally-active ovarian tumors in 30 years of data (1965-1994)]

INTRODUCTION

Authors have investigated the incidence and distribution of hormonally active ovarian tumors in a 30-year surgical material. Out of 552 ovarian tumors, there were 28 hormonally active tumors (5.07%): 18 granulosa cell tumors, 4 thecomas, 2 arrhenoblastomas, 2 malignant v. Kalden folliculomas. There were laso 2 benign tumors: ectopic adrenal ovarian tumor, and ovarian tube hydatidiform mole. They secrete estrogen and testosterone and their effects are evident: prior to puberty (Praecox pubertas), during the reproductive period, but most often in menopause. In order to make the diagnosis, when uterine hemorrhage occurs, it is necessary to perform explorative curettage, but the tumors must be surgically removed. It is necessary to perform that kind of surgery, which corresponds to the age of the woman. Recurrences may appear even 35 years later.

MATERIAL AND METHODS

Hysterectomy with bilateral adnexectomy was performed in 18 (64.28%) postmenopausal women. In 4 (14.29%) women of reproductive age unilateral adnexectomy was performed, while explorative laparotomy was performed also in 4 (14.29%) women. 5-year survival in the first stage of the disease was 75% (20 women). During the first three years 5 (17.86%) women decreased in the IV stage of the disease, as well as one woman (3.57%) in the II b stage, which makes a total of 6 women (21.43%) with fatal outcome. Ovarian tumors also include hormonally active tumors which secrete female and male sex hormones, and whose effects are evident on hormonal receptors. They are divided into benign or malignant, whereas they are all potentially malignant. We differentiate two groups: 1. Feminizing mesenchymomas, which secrete female sex hormones and 2. Virilizing tumors, which secrete male sex hormones. These tumors may occur prior puberty, during the reproductive period and in the postmenopausal period--senium. They can cause minor, long-term or hemorrhages similar to menstruation, as well as hypertrophy of the myometrium. Glandular cystic hyperplasia occurs often, whereas proliferation is rare. Histopathological findings after surgery (for example of myoma) are often surprising, because they reveal hormonally active undetected ovarian tumors or glandular cystic endometrial hyperplasia. All hormonally active tumors are potentially malignant. The aim of this retrospective study was to compare our prior attitudes and interventions with newer attitudes and to make changes on behalf of our patients.

RESULTS

Our investigation included 552 adnexal tumors in a 30-year material. Each woman with uterine hemorrhage had undergone explorative curettage and the material was sent for histopathological analysis. During the investigated period 28 hormonally active tumors were found: 2 benign and 26 malignant or potentially malignant tumors (Table 2). There were 18 cases (40.91%) with granulosa cell tumors, 6 cases (13.64%) with cystadenocarcinoma ovarii serosum; 3 cases (6.82%) with borderline tumors; 4 cases (9.09%) with thecoma of the ovarii. Pseudomucious adenocarcinoma was found in 2 cases (4.55%) as well as endometrial adenocarcinoma, malignant mesenchymoma, arrhenoblastoma, malignant folliculoma v. Kalden; whereas malignant teratoma was established in 1 case (2.27%), as well as anaplastic carcinoma, metastatic carcinoma--Krunberg. It is obvious that hormonally active tumors make almost half of the cases (46.43%) and occur mostly at the age of 50-59 years of age (3.4%). Out of 28 patients, 18 underwent hysterectomy and bilateral adnexectomy (64.28%); 4 (14.29%) underwent unilateral adnexectomy that is explorative laparotomy for taking bioptic samples for histological examination (14.29%). Out of 28 patients, 4 were women of reproductive age. All of them underwent adnexectomy and are alive. Hemorrhages usually occur a few years after menopausal period. In one case it occurred 35 years after menopause (arrhenoblastoma), in another 25 years after menopause due to endometrial carcinoma asso

[Analysis of pathohistological results from the uterine mucosa 1965-1998 at the gynecology department in Senta]

INTRODUCTION

It is a well known fact that there is no invasive uterine carcinoma which was not a "carcinoma in situ" in the initial stage. On the basis of this knowledge it is evident that active systematic detection of malignant uterine neoplasms is of great importance. Incidence of cervical carcinoma had been at the first place for years, but in the last 10 years the number of diagnosed cancer of corpus uteri has significantly increased. Uterine hemorrhage is a problem at any age, but at menopause and senium it is of special importance, because at this age every hemorrhage must be considered carcinomatous, unless something else is established (1). Out of all methods, histopathological analysis of the biopsy material is the most reliable, but only complete, not fractional, uterine abrasion has a full diagnostic value. Explorative curettage was performed in all cases of polypectomies and cervix biopsies (2,3,4).

MATERIAL AND METHODS

A retrospective study included all histopathological findings of curettages, polypectomies and biopsies performed due to hemorrhage in the period from 1965 to 1998. During this period 48,606 women were hospitalized at the Gynecology Department of the General Hospital in Senta. 9,475 (19.49%) underwent explorative curettage, partly for therapeutic and partly for diagnostic reasons. The biopsy material was sent for histopathological analysis, disregarding the quantity and macroscopic appearance.

RESULTS

The greatest number of explorative curettages were performed in women from 41-50 years of age (41.35%). The number of interventions decreased in the sixth and seventh decade, with sudden increase over 70 years of age. The greatest number of functional bleeding occurred in women from 21 to 50 years of age (33.59%), whereas endometrial hyperplasia was diagnosed in 22.6% of patients 41-50 years of age. Biopsies and polypectomies with explorative curettages were most frequent in patients 61-70 years of age. Uterine carcinoma was diagnosed in 470 patients: out of this number cervical carcinoma was diagnosed in 234 patients, and corpus uteri carcinoma in 236 women. Cervical carcinoma occurred most frequently in the group of patients 41-50 years of age, whereas corpus uteri carcinoma was most frequent in the group 51-70 years of age. It is important to point out the correlation between cervical carcinoma and corpus uteri carcinoma being 1:1.04.

CONCLUSION

1. In order to detect corpus uteri carcinoma, especially in women over 40 years of age, it is necessary to pay special attention to all kinds of uterine bleedings. 2. Explorative curettage of the whole uterine cavity and histopathological analysis of biopsy material are considered to be the most reliable diagnostic methods for detection of carcinoma. 3. The correlation between cervical carcinoma and corpus uteri carcinoma is 1:1.04. It points to a difference in regard to corpus uteri carcinoma established in previous studies.

Cell type and pathway dependence of synaptic AMPA receptor number and variability in the hippocampus

It has been suggested that some glutamatergic synapses lack functional AMPA receptors. We used quantitative immunogold localization to determine the number and variability of synaptic AMPA receptors in the rat hippocampus. Three classes of synapses show distinct patterns of AMPA receptor content. Mossy fiber synapses on CA3 pyramidal spines and synapses on GABAergic interneurons are all immunopositive, have less variability, and contain 4 times as many AMPA receptors as synapses made by Schaffer collaterals on CA1 pyramidal spines and by commissural/ associational (C/A) terminals on CA3 pyramidal spines. Up to 17% of synapses in the latter two connections are immunonegative. After calibrating the immunosignal (1 gold = 2.3 functional receptors) at mossy synapses of a 17-day-old rat, we estimate that the AMPA receptor content of C/A synapses on CA3 pyramidal spines ranges from <3 to 140. A similar range is found in adult Schaffer collateral and C/A synapses.

NSF binding to GluR2 regulates synaptic transmission

Here, we show that N-ethylmaleimide-sensitive fusion protein (NSF) interacts directly and selectively with the intracellular C-terminal domain of the GluR2 subunit of AMPA receptors. The interaction requires all three domains of NSF but occurs between residues Lys-844 and Gln-853 of rat GluR2, with Asn-851 playing a critical role. Loading of decapeptides corresponding to the NSF-binding domain of GluR2 into rat hippocampal CA1 pyramidal neurons results in a marked, progressive decrement of AMPA receptor-mediated synaptic transmission. This reduction in synaptic transmission was also observed when an anti-NSF monoclonal antibody (mAb) was loaded into CA1 neurons. These results demonstrate a previously unsuspected direct interaction in the postsynaptic neuron between two major proteins involved in synaptic transmission and suggest a rapid NSF-dependent modulation of AMPA receptor function.

Identification of lectin-purified neural glycoproteins, GPs 180, 116, and 110, with NMDA and AMPA receptor subunits: conservation of glycosylation at the synapse

The postsynaptic apparatus is associated with a number of glycoproteins with apparent molecular masses of 180, 116, and 110 kDa, which are highly concentrated in and may be uniquely associated with this structure. These glycoproteins, purified by concanavalin A lectin-affinity chromatography, showed immunoreactivity in the present study with subunit-specific antibodies to glutamate receptors as follows: GP 180, NMDA receptor subunits NR2A/NR2B; GP 116, NMDA receptor NR1 (1a); and GP 110, pan-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (pan-AMPA) receptors. Sensitivities to the glycosidases peptide N-glycosidase F and endo-beta-N-acetylglucosaminidase H on both western blots and silver-stained gels suggested that the glutamate receptors were at least major constituents of the glycoprotein bands. Similar detailed glycosylation was observed for all three glycoproteins, with neutral oligosaccharides being dominant. Oligomannosidic glycans (with from five to nine mannoses) accounted for approximately 50% of the neutral sugars, with Man 5 (at almost 20% of the neutral sugars) always the major glycan. Other abundant neutral oligosaccharides were of the complex type. Similar sensitivities to peptide N-glycosidase F and endo-beta-N-acetylglucosaminidase H were observed for cell line-expressed NMDA receptor subunits, suggesting that irrespective of the glycosylation processing available, the least highly processed oligosaccharides will be expressed. This may be indicative of glycosylation sites in these receptors that are inaccessible to the later processing enzymes and favours the oligomannosidic class of glycans in functional roles.

Localization of the glutamate receptor subunit GluR1 on the surface of living and within cultured hippocampal neurons

The distribution of the glutamate receptor subunit GluR1 was investigated in cultured hippocampal neurons by confocal microscopy, using polyclonal antibodies directed against either the N- or C-terminal region. On living neurons, GluR1 immunofluorescence was detected with the N-terminal antibody only. GluR1 was localized in a highly punctate manner on the surface of neuronal soma and throughout the dendritic tree. Many GluR1 puncta co-localized with the synaptic marker synaptophysin, although extrasynaptic GluR1 puncta were also observed. A comparison of GluR1 subunit distribution of living neurons labelled with N-terminal antibody with that obtained after the cells had been fixed, permeabilized and subsequently reacted with C-terminal or additional N-terminal antibody showed a number of differences. In permeabilized cells additional, diffuse labelling was observed which was very pronounced in the soma and extended into the proximal dendrites. Furthermore, some spines showed little or no labelling of their membrane surface, but labelled strongly after the cells had been fixed and permeabilized. Such spines may be the postsynaptic components of silent or suboptimal synapses.

Expression of raf serine/threonine protein kinases in the cell bodies of primary sensory neurons of the adult rat

We have used immunocytochemistry to examine the distribution of raf protein kinases in sensory neurons of the adult rat. In lumbar and trigeminal sensory ganglia, cells of all size ranges appeared to be raf immunoreactive and this was confirmed by double labeling using subpopulation specific markers. Almost all cells labeled with Griffonia simplicifolia IB4 (a small cell marker) or immunostained by using a large cell marker (RT97) showed raf immunoreactivity. These two markers label cells known to differ in their expression of neurotrophin receptors (trk). Thus raf kinases are not confined to cells expressing only certain trk subtypes. In the dorsal horn of the spinal cord, raf immunoreactivity was present in scattered neurons. However, sensory axons identified by IB4 histochemistry were devoid of raf immunostaining. Lectin-labeled nerve fibers in the cornea, lower lip and glans penis were also not immunoreactive. Ligation of the sciatic nerve did not produce any accumulation of raf immunoreactivity, confirming that raf kinases are not axonally transported to the peripheral processes of sensory neurons. Surgical dissection of the sciatic nerve caused the normal homogeneous cytoplasmic raf immunoreactivity to be replaced in some cells by a staining concentrated predominantly under the plasma membrane. One possibility is that this represents activation of raf in these cells.

The C-terminal domain of glutamate receptor subunit 1 is a target for calpain-mediated proteolysis

The AMPA receptors are glutamate-gated ion channels mediating synaptic transmission at the majority of excitatory synapses in the mammalian CNS. They are composed of four subunits (GluR1-4) which exist in two alternatively spliced variants (flip and flop) and are generally considered to form pentameric receptors. The transmembrane structure of the receptors remains a matter of controversy as some data suggest a transmembrane topology consisting of five, four, or three membrane spanning regions. Some receptor properties have been shown to be regulated by phosphorylation processes as well as by the phospholipid environment. More recently, we have shown that calcium treatment of thin (10 microns) frozen-thawed brain sections resulted in profound modifications of the immunochemical properties of the AMPA receptors. More specifically, immunolabelling of the AMPA receptors with antibodies directed against the C-terminal domain of GluR1 and GluR2/3 was markedly decreased in dendritic fields following such treatment at 35 degrees C. This effect was temperature-dependent and completely blocked by inhibitors of the calcium-dependent proteases calpains, and we suggested that calpains are involved in the regulation of AMPA receptor properties. The results of the present study demonstrate that calpain activation produces a partial proteolysis in the C-terminal domain of the receptors and generates a new receptor species with an apparent molecular weight of 103,000 mol. wt. Sequence analysis of the GluR1 C-terminal domain suggests a couple of cleavage sites for calpains. These results are of particular interest considering the body of evidence implicating calpains and changes in excitatory amino acid receptors in mechanisms of synaptic plasticity as well as in neurodegenerative processes.

Immunological relatedness of the sarcoplasmic reticulum Ca(2+)-ATPase and the Na+,K(+)-ATPase

The effect of anti-ATPase antibodies with epitopes near Asp-351 (PR-8), Lys-515 (PR-11) and the ATP binding domain (D12) of the Ca(2+)-ATPase of sarcoplasmic reticulum (EC 3.6.1.38) was analyzed. The PR-8 and D12 antibodies reacted freely with the Ca(2+)-ATPase in the native membrane, indicating that their epitopes are exposed on the cytoplasmic surface. Both PR-8 and D12 interfered with the crystallization of the Ca(2+)-ATPase, suggesting that their binding sites are at interfaces between ATPase molecules. PR-11 had no effect on ATPase-ATPase interactions or on the ATPase activity of sarcoplasmic reticulum. The epitope of PR-11 is suggested to be the VIDRC sequence at residues 520-525, while that of D12 at residues 670-720 of the Ca(2+)-ATPase. The use of predictive algorithms of antigenicity for identification of potential antigenic determinants in the Ca(2+)-ATPase is analyzed.

Polarized infrared attenuated total reflectance spectroscopy of the Ca(2+)-ATPase of sarcoplasmic reticulum

The mean orientations of the transition dipole moments associated with vibrational modes of the proteins and phospholipids of sarcoplasmic reticulum were determined on dry and hydrated membrane multilayers deposited on germanium or zinc selenide crystals, using polarized infrared attenuated total reflectance spectroscopy (P-IR-ATR). For preservation of the enzymatic activity of the Ca(2+)-ATPase the films were prepared from solutions containing 0.05 M KCl, 5 mM imidazole (pH 7.4), 0.5 mM MgCl2, 1-10 mM trehalose and dithiothreitol. The anisotropy was highest in dry films containing congruent to 7.5 micrograms protein/cm2, and decreased with increasing membrane thickness or hydration. The dichroic ratio of the CH2 vibrations (2923 cm-1) of extracted sarcoplasmic reticulum phospholipids on Ge plate was 1.56, compared with a dichroic ratio of 1.68 obtained on dry films of whole sarcoplasmic reticulum. The dichroic ratios of the amide I band (1650 cm-1) of the Ca(2+)-ATPase in the Ca2-E1 state and in the EGTA and vanadate stabilized E2-V state were nearly identical (1.60 vs. 1.62). The dichroism of the amide I, amide II and lipid CH2 vibrations was not affected by changes in the concentration of KCl (25-100 mM) or Ca2+ (approximately equal to 10(-8)-10(-4) M) and by the addition of vanadate (1 mM) or Pi (5 mM) in a calcium-free medium containing 0.5 mM EGTA. The dichroic ratio of the C-C (1033 cm-1) or CO stretching band (1046 cm-1) of trehalose incorporated into SR films was 1.2 on Ge plate; this corresponds to a mean angle of approximately 70 degrees between the plane of the trehalose ring and the normal of the film plane, suggesting that the trehalose molecules are surprisingly well oriented in the polar headgroup region of the phospholipids. The orientation of the trehalose was not affected by the presence of Ca(2+)-ATPase.

Covalent labeling of the cytoplasmic or luminal domains of the sarcoplasmic reticulum Ca(2+)-ATPase with fluorescent azido dyes

Sarcoplasmic reticulum (SR) vesicles were incubated with azido derivatives of Cascade blue (ACB), Lucifer yellow (ALY), 2,7-naphthalene-disulfonic acid (ANDS), and fluorescein (AF) for 0.1-24 h at 2 degrees C. All four dyes gave intense reaction with the cytoplasmic domain of the Ca(2+)-ATPase on photoactivation after brief incubation. The penetration of the dyes into the luminal space of the SR was determined after centrifugation through Sephadex microcolumns to remove the external dye, followed by photolabeling and gel electrophoresis of the photolabeled proteins. The reaction of ACB and ANDS with the Ca(2+)-ATPase and with calsequestrin increased progressively during incubation up to 24 h indicating their slow accumulation in the luminal space, while ALY and AF did not show significant penetration into the vesicles. The distribution of the covalently attached ACB in the Ca(2+)-ATPase was tested by tryptic proteolysis after labeling exclusively from the outside (OS), from the inside (IS) or from both sides (BS). In all cases intense ACB fluorescence was seen in the A fragment with inhibition of ATPase activity. In the OS preparations the A1, while in IS the A2 fragment was more intensely labeled. There was no significant incorporation of ACB into the region of B fragment identified by FITC fluorescence. The crystallization of the Ca(2+)-ATPase by EGTA + decavanadate was completely inhibited in the BS samples after labeling either in the Ca2E1 or E2V conformation. There was no inhibition of crystallization in the OS preparations. In the IS preparations labeled in the Ca2E1 state the crystallization was impaired, while in the E2V state there was only slight disorganization of the crystals. The total amount of ACB photoincorporated into SR proteins after incubation for 24 h was 1.75 nmol/mg protein; 2/3 of this labeling occurred from the outside and 1/3 from the inside. Similar level of labeling was obtained in media that stabilize the E1 or the E2 conformation of the Ca(2+)-ATPase.

Differences in the susceptibility of various cation transport ATPases to vanadate-catalyzed photocleavage

Illumination of sarcoplasmic reticulum vesicles by ultraviolet light in the presence of 1 mM vanadate causes photocleavage of the Ca(2+)-ATPase into two fragments (Vegh et al. (1990) Biochim. Biophys. Acta 1023, 168-183). In the absence of Ca2+ the photocleavage occurs in the N-terminal half of the molecule near the phosphate acceptor Asp-351. In the presence of 2 mM Ca2+ the photocleavage shifts to the C-terminal half of the ATPase, near the FITC binding site (Lys-515). About half of the Ca(2+)-ATPase was cleaved rapidly, accompanied by nearly complete, irreversible loss of ATPase activity when illuminated in the presence of 2 mM CaCl2; further cleavage of the enzyme was slow and affected primarily the C-terminal fragment produced in the presence of Ca2+. Solubilization of the Ca(2+)-ATPase with C12E8 did not affect the site of photocleavage in either conformation. The vanadate-induced Ca(2+)-ATPase crystals were disrupted during photocleavage, while the binding of anti-ATPase antibodies directed against the phosphorylation site (PR-8) and against the FITC binding region (PR-11) was enhanced. The bovine kidney Na+,K(+)-ATPase was insensitive to photocleavage under conditions where about half the Ca(2+)-ATPase was fragmented. The slight cleavage of the pig gastric H+,K(+)-ATPase after prolonged illumination produced fragments that are distinct from the fragments of the Ca(2+)-ATPase.

Emerging views on the structure and dynamics of the Ca2(+)-ATPase in sarcoplasmic reticulum

The ATP-dependent Ca2+ transport in sarcoplasmic reticulum involves transitions between several structural states of the Ca2(+)-ATPase, that occur without major changes in the secondary structure. The rates of these transitions are modulated by the lipid environment and by interactions between ATPase molecules. Although the Ca2(+)-ATPase restricts the rotational mobility of a population of lipids, there is no evidence for specific interaction of the Ca2(+)-ATPase with phospholipids. Fluorescence polarization and energy transfer (FET) studies, using site specific fluorescent indicators, combined with crystallographic, immunological and chemical modification data, yielded a structural model of Ca2(+)-ATPase in which the binding sites of Ca2+ and ATP are tentatively identified. The temperature dependence of FET between fluorophores attached to different regions of the ATPase indicates the existence of 'rigid' and 'flexible' regions within the molecule characterized, by different degrees of thermally induced structural fluctuations.

The binding of monoclonal and polyclonal antibodies to the Ca2(+)-ATPase of sarcoplasmic reticulum: effects on interactions between ATPase molecules

We analyzed the interaction of 14 monoclonal and 5 polyclonal anti-ATPase antibodies with the Ca2(+)-ATPase of rabbit sarcoplasmic reticulum and correlated the location of their epitopes with their effects on ATPase-ATPase interactions and Ca2+ transport activity. All antibodies were found to bind with high affinity to the denatured Ca2(+)-ATPase, but the binding to the native enzyme showed significant differences, depending on the location of antigenic sites within the ATPase molecule. Of the seven monoclonal antibodies directed against epitopes on the B tryptic fragment of the Ca2(+)-ATPase, all except one (VIE8) reacted with the enzyme in native sarcoplasmic reticulum vesicles in both the E1 and E2V conformations. Therefore these regions of the Ca2(+)-ATPase molecule are freely accessible in the native enzyme. The monoclonal antibody VIE8 bound with high affinity to the Ca2(+)-ATPase only in the E1 conformation stabilized by 0.5 mM Ca2+ but not in the E2V conformation stabilized by 0.5 mM EGTA and 5 mM vanadate. Several antibodies that reacted with the B fragment interfered with the crystallization of Ca2(+)-ATPase in the presence of EGTA and vanadate and at least two of them destabilized preformed Ca2(+)-ATPase crystals, suggesting inhibition of interactions between ATPase molecules. Of five monoclonal antibodies with epitopes on the A1 tryptic fragment of the Ca2(+)-ATPase only one gave strong reaction with the native enzyme, and none interfered with ATPase-ATPase interactions as measured by the polarization of fluorescence of FITC-labeled Ca2(+)-ATPase. Therefore the regions of the molecule containing these epitopes are relatively inaccessible in the native structure. Partial tryptic cleavage of the Ca2(+)-ATPase into the A1, A2 and B fragments did not promote the reaction of anti-A1 antibodies with sarcoplasmic reticulum vesicles, but solubilization of the membrane with C12E8 rendered the antigenic site fully accessible to several of them, suggesting that their epitopes are located in areas of contacts between ATPase molecules. Two monoclonal anti-B antibodies that interfered with ATPase-ATPase interactions, produced close to 50% inhibition of the rate of ATP-dependent Ca2+ transport, with significant inhibition of ATPase; this may suggest a role for ATPase oligomers in the regulation of Ca2+ transport. The other antibodies that interact with the native Ca2(+)-ATPase produced no significant inhibition of ATPase activity even at saturating concentrations; therefore their antigenic sites do not undergo major movements during Ca2+ transport.

Vanadate-catalyzed, conformationally specific photocleavage of the Ca2(+)-ATPase of sarcoplasmic reticulum

Vanadate-sensitized photocleavage of the Ca2(+)-ATPase of rabbit sarcoplasmic reticulum was observed upon illumination of sarcoplasmic reticulum vesicles or the purified Ca2(+)-ATPase by ultraviolet light in the presence of 1 mM monovanadate or decavanadate. The site of the photocleavage is influenced by the Ca2+ concentration of the medium. When the [Ca2+] is maintained below 10 nM by EGTA, the vanadate-catalyzed photocleavage yields fragments of approximately equal to 87 and approximately equal to 22 kDa, while in the presence of 2-20 mM Ca, polypeptides of 71 and 38 kDa are obtained as the principal cleavage products. These observations indicate that the site of the vanadate-catalyzed photocleavage is altered by changes in the conformation of Ca2(+)-ATPase. Selective tryptic proteolysis, at Arg-505-Ala-506, combined with covalent labeling of Lys-515 by fluorescein 5'-isothiocyanate and with the use of anti-ATPase antibodies of defined specificity, permitted the tentative allocation of the sites of photocleavage to the A fragment near the T2 cleavage site in the absence of Ca2+, and to the B fragment between Lys-515 and Asp-659 in the presence of 2-20 mM Ca2+. The loss of ATPase activity during illumination is accelerated by calcium in the presence of vanadate. The vanadate-catalyzed photocleavage in the presence of Ca2+ is consistent with the existence of an ATPase-Ca2(+)-vanadate complex (Markus et al. (1989) Biochemistry 28, 793-799).

Sarcoplasmic reticulum (SR) Ca2(+)-ATPase as a marker of muscle cell differentiation: immunohistochemical investigations of rhabdomyosarcomas and enhancement of the immunostaining after sodium methoxide pretreatment

An immunocytochemical investigation of sarcoplasmic reticulum (SR) Ca2(+)-ATPase (SR-Ca-ATPase) was performed on formalin-fixed paraffin-embedded specimens of different types of rhabdomyosarcomas such as variants of embryonal and pleomorphic forms. Immunostaining frequency of tumours using SR-Ca-ATPase was compared with that of traditionally used muscle specific markers myoglobin, and desmin. Utilizing the possible cleaving of ester bounds sodium methoxide pretreatment was found to be very effective in enhancement of SR-Ca-ATPase immunostaining reaction. In 11 of 15 tissue specimens of 5 cases round shaped and elongated rhabdomyoblasts with definite cytoplasm exhibited positive immunoreactions with all of the polyclonal antibodies tested, using the streptavidin-biotinylated peroxidase complex (S-ABC-method). In formalin-fixed and paraffin-embedded material of 2 cases of undifferentiated rhabdomyosarcomas composed of small round tumour cells with scanty cytoplasm pretreatment with sodium methoxide induced the immunostaining of SR-Ca-ATPase. After that pretreatment a staining of the paranuclear cytoplasm occurred in many of these undifferentiated tumour cells. In these 2 cases, neither myoglobin nor desmin antibodies could react. However, when frozen sections of one of the poorly differentiated tumours were used monoclonal and polyclonal desmin antibodies reacted immunocytochemically in all of the small cells. Sodium methoxide induced or enhanced SR-Ca-ATPase immunocytochemical reaction can be a further addition to the diagnosis of rhabdomyosarcomas in formalin-fixed paraffin-embedded sections, even when desmin antibody fails to react.

Histogenesis of the myeloid system in geese

Using light- and electron-microscopy the location in organs and the time-course of appearance of cells of the myeloid system was studied in goose embryos and goslings. Large numbers of cell forms representing different stages of granulocytopoiesis were found between 15 and 28 days of incubation in the mesenchyma of the kidney and in the reticular tissue of the spleen, but not in the liver and other organs. Thus, before the haemocytopoietic activity of the bone marrow, an activity typical of adult birds, develops, in geese embryonic extra-medullary granulocytopoiesis is characterised by a renal-lienal stage.