S/MAR-binding properties of Sox2 and its involvement in apoptosis of human NT2 neural precursors

DNA fragmentation in apoptosis, especially in lymphocytic cells, is initiated at scaffold/matrix attachment regions (S/MARs) and is preceded by the degradation of nuclear proteins. The present study was performed to establish whether the same mechanism occurred in human NT2 cells subjected to oxygen and glucose deprivation (OGD). We analyzed the integrity of c-myc S/MAR containing a base-unpairing region (BUR)-like element, which we established to be a binding site of the transcription factor Sox2. An accumulation of DNA breaks in close proximity to this element and a degradation of Sox2 were observed early in the OGD-induced apoptotic response. Identification of Sox2 as a novel c-myc BUR-binding protein was achieved through yeast one-hybrid screening and the Sox2/DNA interaction was confirmed by electrophoretic mobility shift assay and immunoprecipitation with Sox2 antibody. Our data support the notion that early proteolysis of unique BUR-binding proteins might represent a universal mechanism that renders these DNA sites vulnerable to endonucleolysis.

An autosomal genomic scan for loci linked to type 2 diabetes in northern Han Chinese

We report the results of a genome-wide scan conducted in 219 individuals from 34 large multiplex nuclear pedigrees from the northern Han Chinese population at an average resolution of about 10 cM. Nonparametric two-point and multipoint linkage analyses were performed to detect evidence of linkage with type 2 diabetes in this study. On chromosome 1 four regions showed evidence of linkage with type 2 diabetes in northern Han Chinese. Of these regions a marker D1S193 (73 cM) showed evidence of linkage (two-point nonparametric linkage 2.409), and another region (around 190 cM) was a replication of several other studies performed in different ethnic populations. Evidences of linkage have been confirmed by typing additional markers (average distance 1-5 cM) flanking these two positive regions on chromosome 1. We also found indication of linkage with type 2 diabetes on chromosomes 2, 10, 12, 18, 20, and 22 by two-point linkage analyses.

Regulation of DNaseY activity by actinin-α4 during apoptosis

DNaseY, a Ca(2+)- and Mg(2+)-dependent endonuclease, has been implicated in apoptotic DNA degradation; however, the molecular mechanisms controlling its involvement in this process have not been fully elucidated. We have obtained evidence from yeast two-hybrid screening and coimmunoprecipitation experiments that DNaseY interacted physically with actinin-alpha4 and this interaction significantly enhanced its endonuclease activity. Accordingly, simultaneous overexpression of both proteins in PC12 cells dramatically increased the rate of apoptosis in response to teniposide' VM26. However, overexpression of DNaseY alone neither triggered apoptosis nor facilitated cell death in response to VM26 or serum deprivation. Instead, the overexpression of DNaseY increased the production of single-strand DNA breaks and evoked a profound upregulation of DNA repair pathways. Taken together, our results point to a novel regulatory mechanism of DNaseY activity and offer an explanation for why cells must first cleave key DNA repair and replication proteins before the successful execution of apoptosis.

Mapping the initial DNA breaks in apoptotic Jurkat cells using ligation-mediated PCR

Apoptotic DNA degradation could be initiated by the accumulation of single-strand (ss) breaks in vulnerable chromatin regions, such as base unpairing regions (BURs), which might be preferentially targeted for degradation by both proteases and nucleases. We tested this hypothesis in anti-Fas-treated apoptotic Jurkat cells. Several nuclear proteins known for their association with both MARs and the nuclear matrix, that is, PARP, NuMA, lamin B and SATB1, were degraded, but the morphological rearrangement of the BUR-binding SATB1 protein was one of the earliest detected changes. Subsequently, we have identified several genes containing sequences homologous to the 25 bp BUR element of the IgH gene, a known SATB1-binding site, and examined the integrity of genomic DNA in their vicinity. Multiple ss breaks were found in close proximity to these sites relative to adjacent regions of DNA. Consistent with our prediction, the results indicated that the initiation of DNA cleavage in anti-Fas-treated Jurkat cells occurred within the BUR sites, which likely became accessible to endonucleases due to the degradation of BUR-binding proteins.

Stimulation of cardiac L-type calcium channels by extracellular ATP

The co-release of ATP with norepinephrine from sympathetic nerve terminals in the heart may augment adrenergic stimulation of cardiac Ca(2+) channel activity. To test for a possible direct effect of extracellular ATP on L-type Ca(2+) channels, single channels were reconstituted from porcine sarcolemma into planar lipid bilayers so that intracellular signaling pathways could be controlled. Extracellular ATP (2-100 microM) increased the open probability of the reconstituted channels, with a maximal increase of approximately 2.6-fold and an EC(50) of 3.9 microM. The increase in open probability was due to an increase in channel availability and a decrease in channel inactivation rate. Other nucleotides displayed a rank order of effectiveness of ATP > alpha,beta-methylene-ATP > 2-methylthio-ATP > UTP > adenosine 5'-O-(3-thiotriphosphate) >> ADP; adenosine had no effect. Several antagonists of P2 receptors had no impact on the ATP-dependent increase in open probability, indicating that receptor activation was not required. These results suggest that extracellular ATP and other nucleotides can stimulate the activity of cardiac L-type Ca(2+) channels via a direct interaction with the channels.

GABA expression dominates neuronal lineage progression in the embryonic rat neocortex and facilitates neurite outgrowth via GABA(A) autoreceptor/Cl- channels

GABA emerges as a trophic signal during rat neocortical development in which it modulates proliferation of neuronal progenitors in the ventricular/subventricular zone (VZ/SVZ) and mediates radial migration of neurons from the VZ/SVZ to the cortical plate/subplate (CP/SP) region. In this study we investigated the role of GABA in the earliest phases of neuronal differentiation in the CP/SP. GABAergic-signaling components emerging during neuronal lineage progression were comprehensively characterized using flow cytometry and immunophenotyping together with physiological indicator dyes. During migration from the VZ/SVZ to the CP/SP, differentiating cortical neurons became predominantly GABAergic, and their dominant GABA(A) receptor subunit expression pattern changed from alpha4beta1gamma1 to alpha3beta3gamma2gamma3 coincident with an increasing potency of GABA on GABA(A) receptor-mediated depolarization. GABA(A) autoreceptor/Cl(-) channel activity in cultured CP/SP neurons dominated their baseline potential and indirectly their cytosolic Ca(2+) (Ca(2+)c) levels via Ca(2+) entry through L-type Ca(2+) channels. Block of this autocrine circuit at the level of GABA synthesis, GABA(A) receptor activation, intracellular Cl(-) ion homeostasis, or L-type Ca(2+) channels attenuated neurite outgrowth in most GABAergic CP/SP neurons. In the absence of autocrine GABAergic signaling, neuritogenesis could be preserved by depolarizing cells and elevating Ca(2+)c. These results reveal a morphogenic role for GABA during embryonic neocortical neuron development that involves GABA(A) autoreceptors and L-type Ca(2+) channels.

Population dynamics of phytophagous and predatory mites (Acari: Tetranychidae, Eriophyidae, Phytoseiidae) on bamboo plants in Fujian, China

The seasonal cycle and population dynamics of Schizotetranychus nanjingensis Ma and Yuan, Aponychus corpuzae Rimando (Tetranychidae), Aculus hambusae Kuang (Eriophyidae) and their natural enemy Tvphlodromus bambusae Ehara (Phytoseiidae) were studied during 1996-1998 in moso bamboo forests in Nanping, Fujian, China. Damage to bamboo leaves was often caused by mixed populations of the three phytophagous species, which displayed different seasonal dynamics: S. nanjingensis fed actively and reproduced in May and from late July to late October (aestivating from June to mid July), Ap. corpuzae was active and reproduced from mid July to late November, and Ac. bambusae from July to next February. During Spring S. nanjingensis was the dominant species with the greatest niche width, but in Summer Ac. bambusae and Ap. corpuzae became dominant and had greater niche widths. In Autumn, Ac. bambusae decreased but both S. nanjingensis and Ap. corpuzae mites increased and the latter became dominant. In winter all species decreased sharply in number. The two spider mite species (S. nanjingensis and Ap. corpuzae) had high niche overlaps in all four seasons. Niche overlaps between the eriophyid Ac. bambusae and the two spider mites were similarly high except during the spring when Ac. bambusae was absent. The predatory mite (T. bambusae) had higher niche overlap with Ap. corpuzae than with others during Autumn and Winter, but during Spring and Summer niche overlap was higher with S. nanjingensis.

[Inhibitory effect of paeonol on lipid peroxidational reaction and oxidational decorate of low density lipoprotein]

OBJECTIVE

To observe the effects of paeonol(Pae) on lipid peroxidational reaction and oxidational decorate of low density lipoprotein(LDL).

METHOD

The rat model of hyperlipidaemia was established by feeding high lipid diet with cholesterol for 6 weeks. The contents of malondialdehyde(MDA) and oxidized low density lipoprotein(OX-LDL) were measured by thiobarbituric acid reactive substance(TBA) method and sandwich method of enzyme-linked immunosorbent assay for detection of polyclone antibody. LDL of serum in healthy person was separated by improve precipitate method.

RESULTS

Pae(300, 150 mg.kg-1) could reduce significantly the levels of MDA of serum, aorta and liver; Pae(300 mg.kg-1) decreased obviously the content of OX-LDL of plasma; Pae(1,000, 200, 40 micrograms.ml-1) refrained markedly the course of oxidational decorate of LDL of serum in healthy person.

CONCLUSION

Pae could reduce the levels of MDA and OX-LDL in hyperlipidaemia rats, and refrain the oxidational decorates of LDL of serum in healthy person.

Functional ionotropic glutamate receptors emerge during terminal cell division and early neuronal differentiation of rat neuroepithelial cells

Ionotropic glutamate receptors mediate fast forms of excitatory synaptic transmission in mature neurons and may play critical roles in neuronal development. However, the developmental stage at which neuronal cells begin to express functional receptors and their roles in lineage progression remain unclear. In the present study, neural precursor cells were isolated from the cortical neuroepithelium of embryonic day 13 rats, and rapidly expanded in serum-free medium in response to basic fibroblast growth factor. RT-PCR revealed the presence of mRNAs encoding AMPA(A), AMPA(C), KA(1), KA(2), NMDA(1), and NMDA(2D) subunits after 3 days in culture. The functional expression of AMPA/kainate and NMDA receptors was investigated using Ca(2+) imaging and whole-cell patch-clamp recording techniques in cells pulse-labeled with bromodeoxyuridine (BrdU) for 1-4 hr. The recorded cells were then double-immunostained for BrdU incorporation and neuron-specific beta-tubulin (TuJ1). The results show that AMPA/kainate and NMDA induced increases in cytosolic Ca(2+) and inward currents only in differentiating neurons. In contrast, proliferating (BrdU(+)TuJ1(-)) cells failed to respond to any ionotropic glutamate receptor agonists. Interestingly, Ca(2+) imaging revealed that a subpopulation of BrdU(+)TuJ1(+) cells also responded to AMPA, indicating the emergence of functional ionotropic AMPA/kainate receptors during terminal cell division and the earliest commitment to neuronal cell lineage. These in vitro results were supported by flow cytometric sorting of AMPA-responsive cells pulse-labeled with BrdU for 1 hr in vivo, which revealed that functional AMPA receptors appear in BrdU(+)TuJ1(+) cells under physiological conditions and may play a role in terminal cell division.

Effects of cis-unsaturated fatty acids on doxorubicin sensitivity in P388/DOX resistant and P388 parental cell lines

It has been reported that several cis-unsaturated fatty acids (c-UFAs) could increase doxorubicin (DOX) accumulation in cancer cells and hence elevate its cytotoxicity. However, some researchers showed that c-UFA pretreatment did not affect its cytotoxicity in special cell lines. It is possible that the different results occurred due to different cellular characteristics. We hypothesized that c-UFA treatment might modulate the activities of some antioxidant enzymes to affect the resistance of cells to DOX. In the present study, we examined how c-UFA pretreatment affected DOX cytotoxicity on mouse leukemia cell line, P388, and its resistant subline, P388/DOX, which we found to have significantly higher glutathione peroxidase (GPx) activity as well as P-glycoprotein (p-gp) overexpression. We chose two c-UFAs, gamma-linolenic acid (GLA) (18:3n-6) and docosahexaenoic acid (DHA) (22:6n-3). Cytotoxicity was measured by MTT (3-(4.5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and trypan blue exclusion assays. DOX accumulation and p-gp expression were measured by flow cytometry. The activities of catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and GPx were determined for both cell lines with and without treatment with GLA or DHA. Significant DOX accumulation occurred in both cell lines with GLA or DHA pretreatment, but without any change in p-gp expression in either cell line. Sensitivity to DOX cytotoxicity was improved by GLA or DHA pretreatment in P388/DOX in which only SOD activity was significantly increased, but not in the parental cell line P388 in which both SOD and CAT were significantly increased by the pretreatment. However, combined pretreatment of GLA or DHA with antioxidants, pyrrolidinedithiocarbamate (PDTC) or Vitamin C, could sensitize not only P388/DOX but also P388 cells to DOX. We conclude that the effects of c-UFA pretreatment on the sensitivity of cancer cells to DOX not only depend on the change in drug accumulation but also the change in the levels of antioxidant enzyme activities, and suggest that combined administration of c-UFAs, antioxidants, and DOX may be more effective in treating leukemia.

Persistent activation of GABA(A) receptor/Cl(-) channels by astrocyte-derived GABA in cultured embryonic rat hippocampal neurons

Whole cell patch-clamp recordings using Cl(-)-filled pipettes revealed more negative levels of baseline current and associated current variance in embryonic rat hippocampal neurons co-cultured on a monolayer of astrocytes than those cultured on poly-D-lysine. These effects were mimicked by culturing neurons on poly-D-lysine in astrocyte-conditioned medium (ACM). The baseline current and variance decreased immediately in all cells after either local perfusion with saline or exposure to bicuculline, an antagonist of GABA at GABA(A) receptor/Cl(-) channels. Baseline current and variance in all cells reached a nadir at approximately 0 mV, the calculated equilibrium potential for Cl(-). Perfusion of ACM rapidly induced a sustained current in neurons, which also reversed polarity at approximately 0 mV. Bicuculline attenuated or eliminated the ACM-induced current at a concentration that completely blocked micromolar GABA-induced current. Quantitative analyses of spontaneously occurring fluctuations superimposed on the ACM-induced current revealed estimated unitary properties of the underlying channel activity similar to those calculated for GABA's activation of GABA(A) receptor/Cl(-) channels. Bicuculline-sensitive synaptic-like transients, which reversed at approximately 0 mV, were also detected in neurons cultured in ACM, and these were immediately eliminated along with the negative baseline current and superimposed current fluctuations by perfusion. Furthermore bicuculline-sensitive synaptic-like transients were rapidly and reversibly triggered when ACM was acutely applied. ACM induced an increase in cytoplasmic Ca(2+) in cultured embryonic hippocampal neurons that was completely blocked by bicuculline and strychnine. We conclude that astrocytes release diffusible substances, most likely GABA, that persistently activate GABA(A) receptor/Cl(-) channels in co-cultured neurons.

Organization and conservation of the GART/SON/DONSON locus in mouse and human genomes

The SON gene, which maps to human chromosome 21q22.1-q22.2, encodes a novel regulatory protein. Here we describe the organization of the Son locus in the mouse genome. The mouse Son gene spans a region of approximately 35 kb. The coding region is more than 8 kb in length and has been completely sequenced. The gene is organized into 11 coding exons and 1 noncoding 3'UTR exon, with over 70% of the coding region residing in one 5.7-kb exon. The gene contains at least one alternative exon, N/C exon 1, which can be used, by splicing, to generate a truncated form of the SON protein. Further investigation of the mouse Son locus has identified the genes directly flanking Son. The glycinamide ribonucleotide formyltransferase gene, Gart, is encoded 5' of Son in a head-to-head arrangement, with the start of both genes lying within 899 bp. Sequence comparison with the expressed sequence tagged database identified a novel gene within 65 bp of the 3' end of Son, which we have named Donson. In this unusually compact gene cluster, we have found overlap in the pattern of expression between Gart, Son, and Donson. However, at least two of these genes have very different functions. While GART is involved in purine biosynthesis, we find that SON shows the characteristics of "SR- type" proteins, which are involved in mRNA processing and gene expression.

Effects of neoplastic transformation and teniposide (VM26) on protein kinase C isoform expression in rodent fibroblasts

This study examined changes in protein kinase C (PKC) isoforms in rodent fibroblasts (rat F111 and mouse NIH3T3), transformed by the polyoma virus middle T antigen (mT) and undergoing apoptosis in response to teniposide (VM26). The mT-transformed cells up-regulated PKC delta and down-regulated both PKC epsilon and PKC lambda expression, and were more sensitive to the drug than their non-transformed counterparts. The drug treatment further lowered the expression of PKC epsilon, triggered nuclear translocation of PKC delta and its site-specific proteolysis, consistent with the notion that changes in specific PKC isoforms play a role not only in the neoplastic transformation of fibroblasts, but also in their apoptotic response.

Synaptic connectivity in hippocampal neuronal networks cultured on micropatterned surfaces

Embryonic rat hippocampal neurons were grown on patterned silane surface in order to organize synapse formations in a controlled manner. The surface patterns were composed of trimethoxysilylpropyl-diethylenetriamine (DETA) lines separated by tridecafluoro-1,1,2,2-tetrahydrooctyl-1-dimethylchlorosilane (13F) spaces. Pre- and post-synaptic specializations were identified by immunostaining for synapsin I and microtubule-associated protein-2 (MAP-2). Functional synaptic connections were examined by recording simultaneously from pairs of neurons using the whole-cell configuration of the patch-clamp technique. Spontaneous and evoked synaptic currents were recorded in neurons cultured for 2-14 days. The formation of functional connections was accompanied by the appearance of spontaneous synaptic currents (SSCs), which could be detected after approximately 3 days in culture in the absence of evoked synaptic currents (ESCs). ESCs were detected only after approximately 7 days in culture, mostly in the form of unidirectional synaptic connections. Other forms of synaptic connectivity, such as bidirectional and autaptic connections, were also identified. Both transient GABAergic and glutamatergic signals mediated the transmissions between communicating cells. These results demonstrate the combination of various types of synaptic connections forming simple and complex networks in neurons cultured on line (DETA)-space (13F) patterns. Finally, precisely synchronized SSCs were recorded in neuron pairs cultured on pattern indicating the existence of a fast-acting feedback mechanism mediated by pre-synaptic GABA(A) receptors.

Acetylcholine stimulates cortical precursor cell proliferation in vitro via muscarinic receptor activation and MAP kinase phosphorylation

Increasing evidence has shown that some neurotransmitters act as growth-regulatory signals during brain development. Here we report a role for the classical neurotransmitter acetylcholine (ACh) to stimulate proliferation of neural stem cells and stem cell-derived progenitor cells during neural cell lineage progression in vitro. Neuroepithelial cells in the ventricular zone of the embryonic rat cortex were found to express the m2 subtype of the muscarinic receptor. Neural precursor cells dissociated from the embryonic rat cortical neuroepithelium were expanded in culture with basic fibroblast growth factor (bFGF). reverse transcriptase-polymerase chain reaction (RT-PCR) revealed the presence of m2, m3 and m4 muscarinic receptor subtype transcripts, while immunocytochemistry demonstrated m2 protein. ACh and carbachol induced an increase in cytosolic Ca2+ and membrane currents in proliferating (BrdU+) cells, both of which were abolished by atropine. Exposure of bFGF-deprived precursor cells to muscarinic agonists not only increased both cell number and DNA synthesis, but also enhanced differentiation of neurons. These effects were blocked by atropine, indicating the involvement of muscarinic ACh receptors. The growth-stimulating effects were also antagonized by a panel of inhibitors of second messengers, including 1,2-bis-(O-aminophenoxy)-ethane-N,N,N', N'-tetraacetic acid (BAPTA-AM) to chelate cytosolic Ca2+, EGTA to complex extracellular Ca2+, pertussis toxin, which uncouples certain G-proteins, the protein kinase C inhibitor H7 and the mitogen-activated protein kinase (MAPK) inhibitor PD98059. Muscarinic agonists activated MAPK, which was significantly inhibited by atropine and the same panel of inhibitors. Thus, muscarinic receptors expressed by neural precursors transduce a growth-regulatory signal during neurogenesis via pathways involving pertussis toxin-sensitive G-proteins, Ca2+ signalling, protein kinase C activation, MAPK phosphorylation and DNA synthesis.

Apoptosis-related functional features of the DNaseI-like family of nucleases

Rat DNaseYb and its human homolog DHP2 are members of a new family of DNaseI-like endonucleases. They contain all the conserved amino acid residues to engage a DNaseI-like catalytic activity and the same molecular mechanisms of DNA hydrolysis. The sequence similarity can be extended to other families of nucleases, such as FEN-1, DNA polymerases, RNaseH and exonuclease III, involved in the ion-dependent hydrolysis of nucleic acids. Their unique features include the NLS signals that place them in the nuclei and a high content of positively charged amino acid residues that results in their high affinity for the substrate. Their properties are consistent with a role in the early stage DNA degradation during apoptosis. The caspase-DFF45/CIDE-CPAN pathway is most likely involved in the second stage of internucleosomal DNA degradation. However, cells express constitutively multiple transcripts encoding DNA degrading enzymes and related molecules, hence they have the molecular diversity to engage the self-destructive pathway appropriate to a given trigger.

Ionic basis for action potential prolongation by phenylephrine in canine epicardial myocytes

INTRODUCTION

In canine ventricle, alpha-adrenergic agonists prolong action potential duration (APD) without any effect on the action potential notch, suggesting that, in this species, the effect on repolarization might be independent of inhibition of I(to). The present study investigated the action of the alpha-adrenergic agonist phenylephrine on the action potential and the repolarizing currents I(to) and I(K) in isolated canine epicardial myocytes.

METHODS AND RESULTS

Isolated cells from canine epicardial tissue, and Purkinje fibers, were studied with the whole cell, voltage clamp method. Phenylephrine 0.1 microM increased APD by 13% +/- 4% at 90% repolarization without affecting the notch or amplitude. Under voltage clamp, concentrations of phenylephrine as high as 10 microM had no effect on I(to) in canine epicardial myocytes. However, I(to) of isolated canine Purkinje myocytes was reduced to 69% +/- 7% of control by 1 microM phenylephrine. Further studies in canine epicardial myocytes revealed an action of phenylephrine to inhibit I(K), and in particular I(Ks). Using a voltage protocol that included a two-step repolarization to separate I(Ks) and I(Kr) tail components, the largely I(Kr) component was not significantly affected by 1 microM phenylephrine, whereas the largely I(Ks) component was reduced to 81% +/- 5% of control value.

CONCLUSION

Alpha-adrenergic prolongation of repolarization in canine epicardium does not result from inhibition of I(to). Rather, it appears that reduction of I(Ks) contributes to the action of phenylephrine. The unresponsiveness of epicardial I(to) is not a general characteristic of the canine heart, because Purkinje myocyte I(to) was inhibited, suggesting regional differences in the molecular basis of I(to) and/or alpha-adrenergic signaling in the canine heart.

Inhibition of spontaneous GABAergic transmission by trimethylolpropane phosphate

Trimethylolpropane phosphate (TMPP) is a neuroactive organophosphate generated during partial pyrolysis of a synthetic ester turbine engine lubricant. While TMPP had been shown to have little affinity for acetylcholinesterase, previous binding studies and 6Cl- flux measurements have implicated TMPP as an antagonist of GABA, receptor/Cl- channels. Using the whole-cell patch clamp method, spontaneous inhibitory postsynaptic currents (sIPSCs) mediated by bicuculline-sensitive GABA(A) receptors were measured in neurons cultured from the rat embryonic hippocampus for 13-21 days. Experiments were conducted in the presence of tetrodotoxin and 6-cyano-7-nitroquinoxaline to inhibit spontaneous presynaptic action potentials and glutamate transmission, respectively, thus isolating GABAergic sIPSCs for study. TMPP induced a concentration-dependent inhibition of sIPSC amplitude and frequency suggesting both postsynaptic and presynaptic actions. Administration of 5 microM TMPP reversibly diminished sIPSC amplitude by 23 +/- 8% (mean SEM, n=5 cells) while markedly decreasing the mean sIPSC frequency by 40 +/- 2% (n=5). The mean time constant of sIPSC decay was reversibly decreased by 20 +/- 4% (n=3) in the presence of 20 microM TMPP, suggesting an increase in the rate of inactivation. To directly verify the blockade of ionotropic GABA receptors by TMPP, the effects of TMPP were examined on whole-cell Cl- current responses activated by exogenous GABA. Administration of TMPP (5 microM) depressed peak whole-cell GABA-induced currents to 73 1% (n=4) of control levels, consistent with the results on sIPSC amplitude. Our data directly demonstrate that TMPP directly inhibits GABA(A) receptor function, as indicated by the blockade of whole-cell GABA-mediated Cl- current and the reduction in sIPSC amplitude. Furthermore, TMPP exerts a presynaptic effect on GABAergic transmission, as evidenced by the reduction in sIPSC frequency, which may be independent of a GABA(A) receptor. The molecular basis for the presynaptic action of TMPP remains to be elucidated.

Glutamate acting at NMDA receptors stimulates embryonic cortical neuronal migration

During cortical development, embryonic neurons migrate from germinal zones near the ventricle into the cortical plate, where they organize into layers. Mechanisms that direct neuronal migration may include molecules that act as chemoattractants. In rats, GABA, which localizes near the target destination for migrating cortical neurons, stimulates embryonic neuronal migration in vitro. In mice, glutamate is highly localized near the target destinations for migrating cortical neurons. Glutamate-induced migration of murine embryonic cortical cells was evaluated in cell dissociates and cortical slice cultures. In dissociates, the chemotropic effects of glutamate were 10-fold greater than the effects of GABA, demonstrating that for murine cortical cells, glutamate is a more potent chemoattractant than GABA. Thus, cortical chemoattractants appear to differ between species. Micromolar glutamate stimulated neuronal chemotaxis that was mimicked by microM NMDA but not by other ionotropic glutamate receptor agonists (AMPA, kainate, quisqualate). Responding cells were primarily derived from immature cortical regions [ventricular zone (vz)/subventricular zone (svz)]. Bromodeoxyuridine (BrdU) pulse labeling of cortical slices cultured in NMDA antagonists (microM MK801 or APV) revealed that antagonist exposure blocked the migration of BrdU-positive cells from the vz/svz into the cortical plate. PCR confirmed the presence of NMDA receptor expression in vz/svz cells, whereas electrophysiology and Ca2+ imaging demonstrated that vz/svz cells exhibited physiological responses to NMDA. These studies indicate that, in mice, glutamate may serve as a chemoattractant for neurons in the developing cortex, signaling cells to migrate into the cortical plate via NMDA receptor activation.

Role of Na-Ca exchange in the action potential changes caused by drive in cardiac myocytes exposed to different Ca2+ loads

The role of Na-Ca exchange in the membrane potential changes caused by repetitive activity ("drive") was studied in guinea pig single ventricular myocytes exposed to different [Ca2+]o. The following results were obtained. (i) In 5.4 mM [Ca2+]o, the action potentials (APs) gradually shortened during drive, and the outward current during a train of depolarizing voltage clamp steps gradually increased. (ii) The APs shortened more and were followed by a decaying voltage tail during drive in the presence of 5 mM caffeine; the outward current became larger and there was an inward tail current on repolarization during a train of depolarizing steps. (iii) These effects outlasted drive so that immediately after a train of APs, currents were already bigger and, after a train of steps, APs were already shorter. (iv) In 0.54 mM [Ca2+]o, the above effects were much smaller. (v) In high [Ca2+]o APs were shorter and outward currents larger than in low [Ca2+]o. (vi) In 10.8 mM [Ca2+]o, both outward and inward currents during long steps were exaggerated by prior drive, even with steps (+80 and +120 mV) at which there was no apparent inward current identifiable as I(Ca). (vii) In 0.54 mM [Ca2+]o, the time-dependent outward current was small and prior drive slightly increased it. (viii) During long steps, caffeine markedly increased outward and inward tail currents, and these effects were greatly decreased by low [Ca2+]o. (ix) After drive in the presence of caffeine, Ni2+ decreased the outward and inward tail currents. It is concluded that in the presence of high [Ca2+]o drive activates outward and inward Na-Ca exchange currents. During drive, the outward current participates in the plateau shortening and the inward tail current in the voltage tail after the action potential.

Kir 4.1 channel expression in neuroblastomaxglioma hybrid NG108-15 cell line

To study a possible involvement of inwardly rectifying K+ 4.1 (Kir 4. 1) channels in neural cell development, RT-PCR, immunocytochemistry and whole-cell patch-clamp techniques were used to assess expression of Kir 4.1 channels in proliferating and differentiated NG108-15 cells. RT-PCR revealed co-expression of Kir 4.1 and rat ether-a-go-go-related gene (R-ERG) mRNAs in both proliferating and differentiated cells. The relative Kir 4.1 mRNA concentration increased markedly as cells progressed from undifferentiated to differentiated cells. Kir 4.1-immunoreactivity was barely detectable in undifferentiated cells, but clearly detected in differentiated cells, indicating that Kir 4.1 gene and protein expressions are developmentally regulated. However, corresponding Kir 4.1 current could not be detected in differentiated cells using whole-cell patch-clamp recording. The 'silent' channel/receptor, often found in tumor cells, may carry genetic defects, which prevent functional expression of the channel. NG108-15 may serve as unique model for studying the relationship between the expression of an ion channel gene and the electrophysiological phenotype it encodes.

A role for inwardly rectifying K+ channels in differentiation of NG108-15 neuroblastoma x glioma cells

The whole-cell patch-clamp technique was used to assess the current carried by inwardly rectifying K+ channels (K(ir)) and the resting membrane potential (RMP) during long-term culture of NG108-15 cells. Culture of this cell line in serum-free medium triggers differentiation of a type I, neuron-like cell type followed by an eventual predominance of a type II, proliferative cell type. NG108-15 K(ir) currents, which strongly resemble currents carried by human ether-a-go-go related gene (HERG) K+ channels, exhibited significantly smaller current density for the more depolarized undifferentiated cells in growth media (GM) and type II cells compared to the neuron-like type I cells. Detailed examination of the transition from undifferentiated GM cells to type I cells revealed a shift in the voltage dependence of K(ir) activation which paralleled the more hyperpolarized RMP, neurite outgrowth, and biochemical differentiation characteristic of type I cells. Reverse-transcription polymerase chain reaction experiments using primers for the rat variant of HERG, RERG, revealed a a nearly twofold increase in RERG mRNA as cells differentiate from GM to type I, a finding entirely consistent with the increased K(ir) current density derived from patch-clamp recordings. Administration of CsCl(5 mM) blocked K(ir) currents and depolarized the RMP of type I cells. Furthermore, culture of NG108-15 cells in serum-free medium but with CsCl added significantly prevented neurite extension, an effect which was entirely reversible upon subsequent removal of CsCl. In contrast, other K+ channel inhibitors (4-aminopyridine and tetraethylammonium), at concentrations without marked effects on K(ir), failed to affect neurite extension. These results suggest an important role of the K(ir) channels in determining the RMP and triggering morphological differentiation of the cell line.

Astrocyte-conditioned saline supports embryonic rat hippocampal neuron differentiation in short-term cultures

Embryonic rat hippocampal neurons were cultured for 1-2 days in serum-free, HEPES-buffered Tyrode's solution. The effects of cortical astrocytes and astrocyte-conditioned saline on neuron survival, membrane surface area and the expression of functional amino acid neurotransmitter receptors were studied. Neurons grown in Tyrode's solution alone survived well for 1 day but deteriorated thereafter both in terms of percent neurons surviving and the amplitudes and densities of GABA-, glycine-, kainate-and NMDA-induced currents. Neurons grown in Tyrode's previously conditioned by astrocytes for 24 h had significantly larger apparent plasma membrane surface area, as indexed by whole-cell membrane capacitance, and larger amplitudes and densities of the amino acid-induced currents after both 1 and 2 days. The survival rate and neurite outgrowth were also greater in the astrocyte-conditioned saline group after 2 days in culture. Similarly, neurons cultured on glass cover-slips facing a confluent monolayer of astrocyte were larger in apparent plasma membrane area and amino acid-induced currents than neurons cultured in Tyrode's alone. Neurons cultured in saline conditioned by astrocytes provide a strategy to study the physiological basis of astrocyte-directed neuronal differentiation in the absence of ambiguities arising from the inclusion of sera and other additives often used in vitro.

Central neuronal synapse formation on micropatterned surfaces

Controlling synapse formation is a key to patterning of neurons into functional circuits and networks in vitro. However, the process of synapse formation among neurons grown on artificial surfaces is relatively unstudied. We cultured embryonic hippocampal cells on trimethoxysilylpropyl-diethylenetriamine (DETA) and tridecafluoro-1, 1,2,2-tetrahydrooctyl-1-dimethylchlorosilane (13F), and on patterns composed of DETA lines separated by 13F spaces. For comparison, neurons were concurrently plated on surfaces coated with uniform poly-d-lysine (PDL). Pre- and postsynaptic specializations were identified by immunostaining for synapsin I and microtubule-associated protein-2 (MAP-2). Spontaneous (SPCs) and evoked (EPCs) postsynaptic currents were recorded using dual patch-clamp techniques. We found that DETA promoted synapse formation, whereas evidence for synapse formation on 13F was barely detected. MAP-2+ neuronal soma and rapidly growing dendrites were co-localized with synapsin I puncta faithfully along DETA lines. The expression of synapsin I puncta, and MAP-2+ soma and dendrites correlated well with the appearance of SPCs. Synapsin I, MAP-2 and SPCs emerged together at days 3-4 and increased at day 7, when EPCs appeared. Synaptic signals occurring during 4-7 days in culture were all GABAergic. These results indicate that fully functional synapses are formed on silane surfaces, demonstrating the suitability of patterned silane surfaces for organizing synapse formation in vitro.