The norbornenyl moiety of cyclothiazide determines the preference for flip-flop variants of AMPA receptor subunits

Cyclothiazide and two analogs in which the norbornenyl part was replaced with a cyclohexyl or a cyclohexenyl moiety were examined with regard to their preference for flop vs. flip splice variants of the (+/-)-alphaamino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subunits GluR2, 3 and 4. The studies were carried out by measuring the effects of the drugs on the binding of [(3)H]AMPA or [(3)H]fluorowillardiine to membranes from HEK293 cells that stably express the AMPA receptor subunits. Cyclothiazide had four to nine times lower EC(50) values at flip than at flop receptors, as previously reported. In contrast, the two analogs showed little discrimination for GluR3 or GluR4 splice variants and a clear preference for the flop variant in the case of GluR2. These results indicate that it is the norbornenyl component of cyclothiazide which confers the selectivity vis-a-vis flip-flop variants.

Arrangement of actin filaments and cytoplasmic granules in the sea urchin egg after TPA treatment

Elongation of microvilli and formation of actin filaments after treatment with a phorbol ester, TPA, were investigated in unfertilized eggs of Hemicentrotus pulcherrimus. Microvilli on the egg surface were examined by scanning electron microscopy. Actin filaments in the cortical layer of the eggs were observed by fluorescence microscopy using rhodamine-labeled phalloidin. The actin molecules were polymerized and bundled to form long filaments inside the cortical layer of eggs after TPA treatment. Arrangement of the actin filaments was followed by spiral elongation of microvilli. Transmission electron microscopic studies showed that the cortical granules under the cell membrane of sea urchin eggs were transferred after TPA treatment from the surface to the interior of the cell [Ciapa et al., 1988: Dev. Biol. 128:142-149]. This movement of the cortical granules was inhibited by cytochalasin B, but not by nocodazole. Furthermore, the distribution of clear granules was changed following TPA treatment. From these results we conclude that intracellular actin filaments may cause the transport of cortical granules and clear granules into the central area of the egg by the activation of protein kinase C. The possible involvement of actin in the inward displacement of granules might be the result of the rearrangement of actin filaments in the cortical layer.

Cytoplasmic Ca2+ oscillation coordinates the formation of actin filaments in the sea urchin eggs activated with phorbol ester

Changes in the intracellular Ca2+ concentration ([Ca2+]i) and the formation of actin filaments were investigated in unfertilized eggs of the sea urchin Hemicentrotus pulcherrimus after activation with a phorbol ester, 12-O-tetradecanoyl phorbol13-acetate (TPA). Intracellular Ca2+ oscillation was observed using a fluorescent Ca2+ indicator dye, calcium green dextran. From about 20 to 80 min after the addition of TPA to 100 microM, there was a rise in [Ca2+]i, which was followed by Ca2+ oscillation. A change in [Ca2+]i in response to TPA was not observed in eggs that had been injected with heparin, an inositol 1,4,5-triphosphate (IP3) receptor antagonist. Therefore, long-term exposure to a high concentration of TPA seems to induce Ca2+ release via the IP3 pathway, as well as causing the release of diacylglycerol from membrane lipids. Moreover, the elongation of actin filaments occurred in the cytoplasm during the rise in [Ca2+]i. Actin filaments also formed when TPA-induced cytoplasmic alkalization was inhibited by exposure to Na(+)-free sea water. These results suggest that the observed cytoplasmic formation of actin filaments may be related to change in the cytoplasmic [Ca2(+)]i, and not intracellular pH, induced by TPA. These phenomena may be similar to the changes in actin construction that occur during cell cycle events.

Detection of mononuclear cells as the source of the increased tissue factor mRNA in the liver from lipopolysaccharide-treated rats

Tissue factor (TF) triggers the coagulation cascade reaction in vivo. Overexpression of TF mRNA is one leading cause of disseminated intravascular coagulation and thrombosis-related organ failure. In response to lipopolysaccharide (LPS) stimulation, various cell types can produce TF mRNA in vitro. However, there is currently no agreement on what types of cells in the liver overexpress TF mRNA after LPS treatment. For the first report, we found the increased TF mRNA with reverse transcription-polymerase chain reaction (RT-PCR), and confirmed a fourfold increase (p<0.001 vs. control, t-test) of the TF mRNA level with RT-competitive PCR in the liver of LPS-treated (2.0 mg/kg i.v. injection) rats. There was no significant difference in the glyceraldehyde-3-phosphate dehydrogenase mRNA level between LPS-treated rats and control rats. To clarify the localization and cellular source of LPS-induced TF mRNA, we performed in situ hybridization analysis with [35S]-labeled oligonucleotides probes, which we originally designed. We detected intense signals of TF mRNA in mononuclear cells but not in endothelial cells around the hepatic vein of LPS-treated rats. In this study, we showed that the TF mRNA level induced by LPS treatment, which may indicate mononuclear cells associated, significantly increased in the liver of rats. These results will provide circumstantial support for the therapeutic strategy that mononuclear cell should be one of the target cells to be treated in the early phase of disseminated intravascular coagulation in the liver, and that the need to suppress its overexpression of TF mRNA is essential for preventing hypercoagulable condition.

Microchip capillary electrophoresis using on-line chemiluminescence detection

Chemiluminescence detection was used in capillary electrophoresis integrated on a microchip. Quartz microchips have two main channels and four reservoirs. Dansyl-lysine and -glycine were separated and detected with bis[(2-(3,6,9-trioxadecanyloxycarbony)-4-nitrophenyl]oxalate as peroxyoxalate chemiluminescent reagent. These dansyl amino acids came into contact with the chemiluminescence reagent to produce visible light at the interface between the separation channel and chemiluminescence reagent-containing reservoir. The detection limit (S/N = 3) for dansyl-lysine was 1 x 10(-5) M, which corresponded to the very small mass detection limit of ca. 0.4 fmol. However, the concentration sensitivity in the present system was approximately two orders of magnitude lower than that in the conventional capillary electrophoresis-chemiluminescence detection system. The relative standard deviations of migration time and peak height for dansyl-lysine were 4.2 and 4.5%, respectively. A channel conditioning before every run and an appropriate control of voltages were needed for the reproducible results. The present system had advantages in rapid separation time (within 40 s), small (several 10 pI) and accurate sample injection method using a cross-shaped injector, and simplification and miniaturization of the detection device.

Fast separation of oligonucleotide and triplet repeat DNA on a microfabricated capillary electrophoresis device and capillary electrophoresis

A laser-induced fluorescence detection system coupled with a highly sensitive silicon-intensified target (SIT) camera is successfully applied to the imaging of a band for DNA fragment labeling by fluorescence dye in a microchannel, and to the visualizing of the separation process on a microfabricated chip. We demonstrated that an only 6 mm separation channel is sufficient for the separation of triplet repeat DNA fragment and DNA molecular marker within only 12 s. The separation using the microfabricated capillary electrophoresis device is confirmed to be at least 18 times faster than the same separation carried out by conventional capillary electrophoresis with 24.5 cm effective length. The use of a short capillary with 8.5 cm effective length is also efficient for fast separation of DNA; however, the microchip technology is even faster than capillary electrophoresis using a short capillary.

Positive modulation of AMPA receptors increases neurotrophin expression by hippocampal and cortical neurons

This study investigated whether positive modulators of AMPA-type glutamate receptors influence neurotrophin expression by forebrain neurons. Treatments with the ampakine CX614 markedly and reversibly increased brain-derived neurotrophic factor (BDNF) mRNA and protein levels in cultured rat entorhinal/hippocampal slices. Acute effects of CX614 were dose dependent over the range in which the drug increased synchronous neuronal discharges; threshold concentrations for acute responses had large effects on mRNA content when applied for 3 d. Comparable results were obtained with a second, structurally distinct ampakine CX546. Ampakine-induced upregulation was broadly suppressed by AMPA, but not NMDA, receptor antagonists and by reducing transmitter release. Antagonism of L-type voltage-sensitive calcium channels blocked induction in entorhinal cortex but not hippocampus. Prolonged infusions of suprathreshold ampakine concentrations produced peak BDNF mRNA levels at 12 hr and a return to baseline levels by 48 hr. In contrast, BDNF protein remained elevated throughout a 48 hr incubation with the drug. Nerve growth factor mRNA levels also were increased by ampakines but with a much more rapid return to control levels during chronic administration. Finally, intraperitoneal injections of CX546 increased hippocampal BDNF mRNA levels in aged rats and middle-aged mice. The present results provide evidence of regional differences in mechanisms via which activity regulates neurotrophin expression. Moreover, these data establish that changes in synaptic potency produce sufficient network level physiological effects for inducing neurotrophin genes, indicate that the response becomes refractory during prolonged ampakine exposure, and raise the possibility of using positive AMPA modulators to regulate neurotrophin levels in aged brain.

Cell fate analysis of teloblasts in the Tubifex embryo by intracellular injection of HRP

As in other clitellate annelids, embryonic development in the oligochaete Tubifex is characterized by the generation of five bilateral pairs of teloblasts (designated M, N, O, P and Q), which serve as embryonic stem cells to produce germ bands on either side of the embryo. A large part of the tissues comprising body segments has been assigned to the progenies of the teloblasts; however, the developmental fate of each teloblast has been inferred only from its initial position in the embryo. In the present study, the fate of the progenies of each teloblast was followed by means of intracellular injection of a tracer enzyme, horseradish peroxidase. Cell fate maps for teloblasts in the Tubifex embryo were constructed. M teloblasts gave rise to nearly all of the mesodermal tissues, which included circular and longitudinal muscles, coelomic walls, nephridia (in segments VII and VIII) and primordial germ cells (in segments X and XI). Although few in number, M teloblasts also contributed cells to the ventral ganglion. Similarly, each of the ectoteloblasts, N, O, P and Q, made a topographically characteristic contribution to the ectodermal tissues such as the nervous system (i.e. ganglionic cells and peripheral neurones) and epidermis, all of which exhibited a segmentally repeated distribution pattern. The P and Q teloblasts uniquely gave rise to additional ectodermal tissues, namely ventral and dorsal setal sacs, respectively. Furthermore, O teloblasts made a contribution to the nephridiopores in segments VII and VIII as well. These results confirm the previously held view that ectoteloblasts and mesoteloblasts are the main source of ectodermal and mesodermal segmental tissues, respectively, but also suggest that all of the teloblasts produce more types of tissue than has previously been thought.

CrkL mediates Ras-dependent activation of the Raf/ERK pathway through the guanine nucleotide exchange factor C3G in hematopoietic cells stimulated with erythropoietin or interleukin-3

CrkL is an SH2 and SH3 domain-containing adaptor protein implicated in pathogenesis of chronic myelogenous leukemia. Here, we demonstrate that overexpression of CrkL enhances the erythropoietin (Epo)- or interleukin (IL)-3-induced activation of Elk-1 and the c-fos gene promoter activity in 32D/EpoR-Wt cells. Moreover, the Epo-induced activation of ERK1 and ERK2 was augmented and prolonged in cells inducibly overexpressing CrkL. A moderate increase in Epo-induced activation of JNK was also observed in cells overexpressing CrkL. Overexpression of C3G enhanced the Elk-1 activation synergistically with CrkL, while a C3G mutant lacking the guanine nucleotide exchange domain showed an inhibitory effect. Studies using a dominant negative Ha-Ras mutant demonstrated that the Elk-1 and ERK2 activation enhanced by CrkL and C3G was dependent on Ras. Consistent with this, the Epo-induced activation of Ras was augmented in cells inducibly overexpressing CrkL. Most importantly, a CrkL mutant defective in the SH2 or N-terminal SH3 domain showed an inhibitory effect on the Epo-induced activation of ERK2. These data indicate that the CrkL-C3G complex plays a role in Epo- or IL-3-induced, Ras-dependent activation of the Raf/ERK pathway leading to the activation of Elk-1 and the c-fos gene transcription.

CrkL activates integrin-mediated hematopoietic cell adhesion through the guanine nucleotide exchange factor C3G

CrkL is a member of the Crk family of adapter proteins consisting mostly of SH2 and SH3 domains. CrkL is most abundantly expressed in hematopoietic cells and has been implicated in pathogenesis of chronic myelogenous leukemia. However, its function has not been precisely defined. Here, we show that overexpression of CrkL enhances the adhesion of hematopoietic 32D cells to fibronectin. The CrkL-induced increase in cell adhesion was blocked by antibodies against VLA-4 (alpha4beta1) and VLA-5 (alpha5beta1) but was observed without changes in surface expression levels of these integrins. Studies using CrkL mutants demonstrated that the SH2 domain is partially required for enhancing cell adhesion, whereas the C-terminal SH3 domain as well as the tyrosine phosphorylation site (Y207) is dispensable. In contrast, the N-terminal SH3 domain, involved in binding C3G and other signaling molecules, was showed to play a crucial role, because a mutant defective of this domain showed an inhibitory effect on the cell adhesion to fibronectin. Furthermore, overexpression of C3G also increased the adhesion of hematopoietic cells to fibronectin, whereas a C3G mutant lacking the guanine nucleotide exchange domain abrogated the CrkL-induced increase in cell adhesion. On the other hand, a dominant negative mutant of H-Ras or that of Raf-1 enhanced the basal and CrkL-induced cell adhesion and that of R-Ras modestly decreased the adhesion. Taken together, these results indicate that the CrkL-C3G complex activates VLA-4 and VLA-5 in hematopoietic cells, possibly by activating the small GTP binding proteins, including R-Ras, through the guanine nucleotide exchange activity of C3G.

[Renin-angiotensin-aldosterone system in the reproductive system]

Besides the circulating renin-angiotensin-aldosterone (R-A-A) system, the tissue R-A-A system has been elucidated to play important roles as autocrines and/or paracrines. The components of R-A-A system are expressed in the ovary, uterus and placenta, indicating the existence of the tissue R-A-A system in these organs. The data indicating the involvement of R-A-A system of these tissues into reproduction have been accumulated. AT2 receptors might modulate the initiation and progression of follicle atresia involving granulosa cell apoptosis. AT2 receptors are expressed abundantly in the uterus and decreased during pregnancy. The placental renin are shown to be secreted into the maternal circulation and elevate blood pressure. It is expected to elucidate the significance of the R-A-A system in the reproductive system.

Synergistic interactions between ampakines and antipsychotic drugs

Tests were made for interactions between antipsychotic drugs and compounds that enhance synaptic currents mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid-type glutamate receptors ("ampakines"). Typical and atypical antipsychotic drugs decreased methamphetamine-induced hyperactivity in rats; the effects of near or even subthreshold doses of the antipsychotics were greatly enhanced by the ampakines. Interactions between the ampakine CX516 and low doses of different antipsychotics were generally additive and often synergistic. The ampakine did not exacerbate neuroleptic-induced catalepsy, indicating that the interaction between the different pharmacological classes was selective. These results suggest that positive modulators of cortical glutamatergic systems may be useful adjuncts in treating schizophrenia.

A clinical study on the magnetic stimulation of the facial nerve

OBJECTIVES

A clinical study on the usefulness of magnetic stimulation of the facial nerve, with special attention paid to the selection of the coil shape and stimulation procedures.

STUDY DESIGN

The subjects consisted of 55 patients with Bell's palsy, 1 patient with a cerebellopontine angle (CPA) tumor, 1 patient with multiple sclerosis (MS), and 30 normal subjects. Three types of coils were used in this study; a 90-mm large single coil, a 40-mm small single coil, and a 20-mm small double coil.

METHODS

The compound muscle action potentials (CMAPs) and long latency response were evoked by transcranial magnetic stimulation (TMS) with a 90-mm large single coil. The 40-mm small single coil was used to test blink reflex by aiming it at the supraorbital nerve as the target site. The subcutaneous activation of the infra-auricular facial nerve was performed with the 20-mm double coil.

RESULTS

The reproducible CMAP and long latency responses were obtained from normal subjects with TMS. However, responses were observed only in patients with relatively mild Bell's palsy. The magnetic stimulation-evoked responses reflected the brainstem function in the patients with a CPA tumor and MS.

CONCLUSION

Although magnetic stimulation remains inferior to conventional electric stimulation in some sense and requires further study, this method is potentially useful because it can stimulate the facial nerve continuously from the cortex to the periphery and can effectively evoke responses reflecting the brainstem function.

beta-adrenergic modulation of L-type Ca2+-channel currents in early-stage embryonic mouse heart

Little information is available concerning the modulation of cardiac function by beta-adrenergic agonists in early-stage embryonic mammalian heart. We have examined the effects of isoproterenol (Iso) on the spontaneous beating rate and action potential (AP) configuration in embryonic mouse hearts at 9.5 days postcoitum (dpc), just 1 day after they started to beat. Iso (3 microM) increased the spontaneous beating rate in whole hearts, dissected ventricles, and isolated ventricular myocytes. In ventricular myocytes, Iso also increased the slope of the pacemaker potential and the action potential duration but decreased the maximum upstroke velocity. In whole cell voltage-clamp experiments, the Ca2+-channel currents were measured as Ba2+ currents (IBa). In 9.5-dpc myocytes, IBa was enhanced significantly from -4.7 +/- 0.9 to -6.7 +/- 1.2 pA/pF (by 52.4 +/- 14.8%, n = 10) after the application of Iso. Propranolol (3 microM) reversed the effect of Iso. Forskolin (For, 10 microM) produced an increase in IBa by 95.5 +/- 18.8% (n = 8). In ventricular myocytes at a late embryonic stage (18 dpc), 3 microM Iso caused an appreciably greater increase in IBa from -6.2 +/- 0.5 to -14.5 +/- 2.2 pA/pF (by 137.8 +/- 33.0%, n = 8), whereas the increase in IBa by 10 microM For (by 120.0 +/- 23.0%, n = 7) was comparable to that observed in the early stage (9.5 dpc). These results indicate that the L-type Ca2+-channel currents are modulated by beta-adrenergic receptors in the embryonic mouse heart as early as 9.5 dpc, probably via a cAMP-dependent pathway.

DNA analysis by microfabricated capillary electrophoresis device

The LIGA (Lithographie Galvanoformung Abformung) process using synchrotron radiation lithography is applied to the microfabrication of capillary array electrophoresis (CAE) device. Laser-induced fluorescence detection system for the CAE device has been constructed by the modification of laser confocal fluorescence microscopy. DNA molecules were detected during migrating in the microchannels filled with polymer separation matrices under electric field to optimize the separation conditions for DNA analysis. Based on this observation, we demonstrated that microfabricated CAE device is realized the fast separation of DNA.

Cardiac malignant pheochromocytoma with bone metastases

A patient with malignant cardiac pheochromocytoma with bone metastases is described. The primary tumor was located between the pulmonary trunk and the left atrium, while metastatic lesions were found in the iliac bones. Treatments with antihypertensive agents, alpha-methylparatyrosine, and combination chemotherapy with cyclophosphamide, vincristine, and dacarbazine partially improved the patient's symptoms, catecholamine levels, and the metastatic lesion of the iliac bones. However, the primary tumor in the heart progressively increased in size and the patient died of disseminated intravascular coagulation and other various complications about 4 years after the diagnosis of the disease.

AMPA receptor desensitization modulates synaptic responses induced by repetitive afferent stimulation in hippocampal slices

In patches excised from CA1 pyramidal cells, peak amplitudes of currents evoked by brief glutamate pulses grew progressively smaller over a series of high-frequency pulses. This decline was eliminated by cyclothiazide, a drug previously shown to block AMPA receptor desensitization. In hippocampal slices, synaptically evoked bursts exhibited an increase from the first to the second response, presumably due to facilitation of transmitter release, but the subsequent responses gradually declined in amplitude. Cyclothiazide attenuated or reversed this decline; after normalization to the first response, the amplitudes of the later responses to a 50 Hz series of afferent stimulation were increased by 20-25% in regular recording medium and by as much as 40% when transmitter release was enhanced in a high-calcium medium. The effect of cyclothiazide was greatly diminished when the stimulation frequency was reduced to 33 or 25 Hz. Comparable results were obtained in slices in which NMDA, GABAA, and GABAB receptors were blocked. The ampakine drug CX516 which has only a minor influence on desensitization kinetics did not differentially facilitate the later responses to high-frequency afferent stimulation. These results suggest that the desensitization of AMPA receptors contributes importantly to synaptic activity when afferents are repetitively activated at high-frequency.

The waveform of synaptic transmission at hippocampal synapses is not determined by AMPA receptor desensitization

Relationships between the kinetic properties of AMPA receptors and the decay phase of fast excitatory transmission were investigated using modulatory drugs. The benzothiadiazide compound cyclothiazide blocked receptor desensitization in patches excised from hippocampus but had only a weak influence on receptor deactivation, i.e., on the decay of responses produced by a 1-ms pulse of glutamate. The ampakine drug CX516 (BDP-12) produced an opposite pattern of effects: a fourfold slowing of deactivation with little change in desensitization. A structurally related drug (CX554 or BDP-20) had prominent effects on both desensitization and deactivation. The halfwidth of field EPSPs measured in the CA1 region of hippocampal slices increased 50-100% in the presence of CX516 or CX554 but by less than 15% at concentrations of cyclothiazide that fully blocked desensitization in patch experiments. These results indicate that receptor deactivation plays a substantially greater role than receptor desensitization in determining the duration of synaptic responses.

[Hemolytic uremic syndrome after bone marrow transplantation]

One hundred and thirteen patients who underwent autologous or allogeneic bone marrow transplantation (BMT) were investigated for the subsequent development of hemolytic uremic syndrome (HUS). HUS developed in seven patients (four males and three females, five acute lymphocytic leukemia (ALL), one acute myelogenous leukemia, one non-Hodgkin's lymphoma) between 36-196 days after BMT. Four patients were recipients of autologous BMT and three were those of allogeneic BMT. Six patients were preconditioned with the regimens including fractionated total body irradiation (TBI). ALL and preconditioning regimen with TBI were suspected to be the risk factors for the development of HUS. Cyclosporin A (CSP) administration was discontinued in three patients who had been given CSP for graft-versus-host disease prophylaxis. Predonisolone was given to the three patients and plasma exchange was performed in one patient. Both hemolytic anemia and thrombocytopenia were resolved in virtually all patients, while creatinine elevation has persisted along with hypertension in one patient.

Lyn physically associates with the erythropoietin receptor and may play a role in activation of the Stat5 pathway

Protein tyrosine phosphorylation plays a crucial role in signaling from the receptor for erythropoietin (Epo), although the Epo receptor (EpoR) lacks the tyrosine kinase domain. We have previously shown that the Jak2 tyrosine kinase couples with the EpoR to transduce a growth signal. In the present study, we demonstrate that Lyn, a Src family tyrosine kinase, physically associates with the EpoR in Epo-dependent hematopoietic cell lines, 32D/EpoR-Wt and F36E. Coexpression experiments in COS7 cells further showed that Lyn induces tyrosine phosphorylation of the EpoR and that both LynA and LynB, alternatively spliced forms of Lyn, bind with the membrane-proximal 91-amino acid region of the EpoR cytoplasmic domain. In vitro binding studies using GST-Lyn fusion proteins further showed that the Src homology (SH)-2 domain of Lyn specifically binds with the tyrosine-phosphorylated EpoR in lysate from Epo-stimulated cells, whereas the tyrosine kinase domain of Lyn binds with the unphosphorylated EpoR. Far-Western blotting and synthetic phosphopeptide competition assays further indicated that the Lyn SH2 domain directly binds to the tyrosine-phosphorylated EpoR, most likely through its interaction with phosphorylated Y-464 or Y-479 in the carboxy-terminal region of the EpoR. In vitro binding studies also demonstrated that the Lyn SH2 domain directly binds to tyrosine-phosphorylated Jak2. In vitro reconstitution experiments in COS7 cells further showed that Lyn induces tyrosine phosphorylation of Stat5, mainly on Y-694, and activates the DNA-binding and transcription-activating abilities of Stat5. In agreement with this, Lyn enhanced the Stat5-dependent transcriptional activation when overexpressed in 32D/EpoR-Wt cells. In addition, Lyn was demonstrated to phosphorylate the EpoR and Stat5 on tyrosines in vitro. These results suggest that Lyn may play a role in activation of the Jak2/Stat5 and other signaling pathways by the EpoR.

Time-resolved fluorescent X-ray interference

A fluorescent X-ray interference method can effectively measure nanometer-level conformational changes for non-crystallized molecules and proteins in aqueous conditions. The time-resolved technique can be used to obtain information about the dynamics of molecules and proteins. Instrumentation for time-resolved fluorescent X-ray interference has been designed. A typical interference-fringe pattern was observed with approximately 3 s of X-ray exposure time from K-fluorescent X-rays emitted from a Zn monoatomic layer on an Rh substrate. The primary X-ray beam was polychromed with a mirror for total external reflection of X-rays and was tuned to an energy level at which only Zn K radiation became optimally excited. The glancing angle of the primary X-ray beam was fixed at a glancing angle at which the total intensity of K-fluorescent X-rays emitted from Zn atoms corresponded to the maximum value. The fluorescent X-ray interference fringes were monitored with an imaging plate (IP) as a non-energy-dispersive two-dimensional detector. The exposed interference fringes on the IP were integrated along the direction of the fringes. The integrated fringes were in close agreement with a theoretical estimate based on the interference among transmitted and reflected waves at interfaces in the sample.

Molecular cloning and nucleotide sequence of the pyruvate kinase gene of an actinomycete Microbispora thermodiastatica

The gene for the thermostable pyruvate kinase of Microbispora thermodiastatica IFO 14046, a moderate thermophilic actinomycete, was cloned in Escherichia coli. This gene consists of an open reading frame of 1422 nucleotides and encodes a protein of 474 amino acids with molecular mass of 50,805 Da. The open reading frame was confirmed as the pyruvate kinase gene by comparison with the N-terminal amino acid sequence of the purified pyruvate kinase from M. thermodiastatica.

Murine cardiac progenitor cells require visceral embryonic endoderm and primitive streak for terminal differentiation

Cardiac progenitor cells in avian and amphibian embryos are known to commit to cardiac lineage during gastrulation or early neurulation. These cells require cell interaction with anterior endoderm for their differentiation into cardiomyocytes. However, little is known about cell interaction in mammalian cardiogenesis. We investigated the staging of murine cardiomyocyte commitment and the role of cell interaction in differentiation of cardiac progenitor cells into cardiomyocytes, using cultures of various embryonic regions at 7.25 and 7.5 days post coitum (p.c.), respectively. To evaluate the terminal differentiation of cardiac progenitor cells, we employed three parameters; expression of spontaneous beating, myosin heavy chain (MHC) protein, and cardiac-specific genes (alpha myosin heavy chain, Csx/Nkx2.5 and myosin light chain 2V genes). mRNAs of cardiac-specific genes were detected in 7.25-day p.c. mesoderm by RT-PCR, suggesting that the genetic specification to cardiac lineage initiated in the mesoderm by 7.25 days p.c. The 7.25-day p.c. isolated mesoderm in 48 hr culture, however, failed to differentiate into spontaneous beating cardiomyocytes and exhibited non-organized MHC protein in 19% of these culture. In contrast, all of the 7.5-day p.c. isolated mesoderm differentiated into beating cardiomyocytes even in 24 hr culture. The 7.25-day p.c. mesoderm associated with primitive streak increased MHC protein expression in 93% of these cultures, although they formed beating foci in 3%. The 7.25-day p.c. explants containing both visceral embryonic endoderm and primitive streak succeeded in terminal differentiation into spontaneous beating cardiomyocytes. Our study suggests that cardiac progenitor cells obtain the potency to complete terminal differentiation autonomously at 7.5 days p.c., as a consequence of the multistep induction by cell interactions with both the primitive streak and visceral embryonic endoderm, following the genetic specification to cardiac lineage in the early gastrula stage.

Erythropoietin and IL-3 induce tyrosine phosphorylation of CrkL and its association with Shc, SHP-2, and Cbl in hematopoietic cells

The present study demonstrates that erythropoietin (Epo) and IL-3 induce tyrosine phosphorylation of the SH2/SH3-containing adapter protein CrkL and its transient association with tyrosine-phosphorylated SHP-2, Shc, and Cbl in a murine IL-3-dependent cell line, 32D, expressing the Epo receptor (EpoR). In these cells, CrkL was constitutively complexed with the guanine nucleotide exchange factor C3G, which was found to coimmunoprecipitate with Shc from Epo- or IL-3-stimulated cells. Studies using cells expressing mutant EpoRs showed that the Epo-induced tyrosine phosphorylation of CrkL is dependent on the membrane-proximal EpoR cytoplasmic region involved in the activation of Jak2 as well as the C-terminal 145 amino acid region which is required for tyrosine phosphorylation of SHP-2 and Shc. It was further revealed that CrkL is recruited to the tyrosine-phosphorylated EpoR, most likely through its interaction with tyrosine-phosphorylated Shc and SHP-2. These results suggest that CrkL is involved in the signaling pathways from the receptors for Epo and IL-3, most likely by modulating the activity of the Ras family GTPases through its interaction with C3G.

Cerebellar ataxia and peripheral neuropathy due to chronic bromvalerylurea poisoning

A patient with chronic bromvalerylurea poisoning showed cerebellar ataxia and peripheral neuropathy. The patient was a 42-year-old Japanese man who developed consciousness disturbance, diplopia, slurred speech, ataxia and gait disturbance after having taken bromvalerylurea for ten years. Magnetic resonance imaging revealed atrophy of the cerebellum and pontine tegmentum. An electrophysiological study revealed decreased motor nerve conduction velocity and amplitude of compound muscle action potentials of the right tibial nerve. Histological findings of the left sural nerve indicated a slightly decreased large myelinated fiber diameter, which suggested chronic axonal damage.

A profile of the behavioral changes produced by facilitation of AMPA-type glutamate receptors

A newly developed group of benzoylpiperidine drugs that enhance AMPA-receptor-gated currents ("ampakines") has been shown to improve memory encoding in rats across a variety of experimental paradigms. The present experiments were intended to i) provide a partial profile of the behavioral changes produced by ampakines, ii) test if two ampakines (BDP-12 and BDP-20) that differ significantly in their effects on AMPA receptor kinetics produce similar behavioral profiles, and iii) determine if physiological potency is reflected in behavioral potency. BDP-20 reduced two measures of exploratory activity in aged rats but increased speed of performance in a radial maze; the drug also caused substantially improved retention of spatial information. These results are similar to those obtained with BDP-12, an analog that differs from BDP-20 in its effects on ligand binding to the AMPA receptor and on the physiological responses of the receptors to glutamate. BDP-20 was approximately ten-fold more potent in behavioral effects than BDP-12, which agrees with the relative potencies of the two drugs as assessed with excised patches and excitatory synaptic responses. These findings indicate that ampakines, though differing in their effects on AMPA-receptor-mediated responses, have similar effects at the behavioral level.

Stable expression of recombinant AMPA receptor subunits: binding affinities and effects of allosteric modulators

Homomeric AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)-type glutamate receptors (GluRs) were stably expressed in kidney cells from cDNAs encoding GluR1 flop, GluR2 flip, GluR2 flop, and GluR3 flop subunits. The recombinant receptors were of the expected size and showed functional properties in whole-cell recording as previously reported. [3H]AMPA binding to all subunits was increased to a similar extent by the chaotropic ion thiocyanate (SCN-). Significant differences were found in the Scatchard plots, however, which were linear and of high affinity for GluR1 and -3 receptors (K(D) values of 33 and 52 nM, respectively) but showed curvature for GluR2 receptors, indicating the presence of two components with distinct affinities. As with brain AMPA receptors, solubilization of GluR2 receptors reduced the number of lower-affinity sites and correspondingly increased the number of higher-affinity sites. The sulfhydryl reagent p-chloromercuriphenylsulfonic acid, which increases binding to brain receptors, produced only minor changes except in the case of GluR2 flip. These results indicate that GluR2, among the subunits examined here, most closely resembles the native AMPA receptors in brain membranes. [3H]AMPA binding was inhibited in a noncompetitive manner by two drugs that change the desensitization kinetics of the AMPA receptor. In agreement with physiological observations, the apparent affinity of cyclothiazide for GluR2 flip (EC50 = 7 microM) was higher than that for receptors made of flop subunits (49-130 microM). In contrast, BDP-37, a member of the benzamide family of drugs, exhibited a lower potency for GluR2 flip (58 microM) than for any of the flop isoforms (18-40 microM). These results predict that the action of centrally active AMPA-receptor modulators varies across brain regions depending on their flip/flop composition.

Purification and characterization of a thermostable pyruvate kinase from the actinomycete Microbispora thermodiastatica

The pyruvate kinase of Microbispora thermodiastatica was purified to homogeneity and some properties of the enzyme were characterized. The molecular weight of the enzyme by gel filtration is 277,000. The subunit molecular weight is 55,000 by SDS-polyacrylamide gel electrophoresis, and only one N-terminal amino acid sequence was obtained. It had a pH optimum around pH 4.5 to 7.0 and was stable over the range of pH 4.0-8.0. The enzyme is thermostable and no activity was lost after heat treatment at 55 degrees C for 60 min. AMP activated this enzyme and the saturation curve of the enzyme for PEP changed from sigmoidal type to hyperbolic type in the presence of AMP.

cDNA cloning, expression and chromosome mapping of the human STAT4 gene: both STAT4 and STAT1 genes are mapped to 2q32.2-->q32.3

Studies of transcriptional activation by interferons and a variety of cytokines have led to the identification of a family of proteins that serve as signal transducers and activators of transcription (STAT). STAT4 is phosphorylated following interleukin (IL)-12 stimulation and is essential for IL-12 signal transduction. The human STAT4 cDNA was cloned, and both STAT4 and STAT1 genes were mapped to human chromosome bands 2q32.2-->q32.3 by fluorescence in situ hybridization. These results suggest that STAT4 and STAT1 may have arisen via a tandem gene duplication. However, human STAT1 is expressed ubiquitously, whereas human STAT4 is expressed in several tissues including spleen, heart, brain, peripheral blood cells, and testis.

Effects of a centrally active benzoylpyrrolidine drug on AMPA receptor kinetics

A newly developed benzoylpyrrolidine drug (BDP-20) that increases the size of fast, excitatory synaptic responses was examined for its effects on the kinetic properties of alpha-amino-3-hydroxy-5-methyl-4-isoxalepropionic acid (AMPA)-type glutamate receptors. When long pulses of glutamate were applied to excised hippocampal patches of the rat, the compound BDP-20 caused an approximately 15-fold reduction in the rate at which responses desensitized and a similar size increase in steady-state currents. In experiments using 1-ms glutamate pulses, BDP-20 prolonged response deactivation by a factor of about four and greatly reduced the depression in the second response when two consecutive glutamate pulses were given. Two types of equilibrium binding assays indicated that BDP-20 causes a measurable increase in the affinity of AMPA receptors; the EC50 values for this effect were similar to those obtained in excised patch studies. The actions of BDP-20 on physiology and ligand binding could be adequately reproduced in a receptor model by slowing the rate of desensitization and increasing the affinity of the sensitized states. The biochemical and physiological effects of this benzoylpyrrolidine compound were qualitatively different from those obtained with cyclothiazide, although both types of drug increased AMPA receptor-mediated synaptic responses. Moreover, interactions between the drugs were at most only partially competitive; AMPA receptors may thus have multiple modulatory sites with distinct drug preferences and different effects on receptor kinetics.

Effect of the AMPA receptor modulator IDRA 21 on LTP in hippocampal slices

IDRA 21 (7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine S,S-dioxide) has been reported to modulate AMPA receptor kinetics and to improve memory in certain animal models. In the present study, its effects on synaptic transmission and long-term potentiation (LTP) were tested in hippocampal slices. IDRA 21 (500 microM) significantly increased the amplitude and halfwidth of field EPSPs. The drug did not affect monosynaptic IPSPs but enhanced disynaptically-induced feedforward IPSPs, presumably by acting on AMPA receptors on interneurons. At concentrations that facilitated synaptic transmission, IDRA 21 promoted the induction of LTP; i.e. full potentiation was obtained with stimulation paradigms that were only partially effective in the absence of drug. The results support the hypothesis that drugs which enhance AMPA receptor-mediated currents facilitate LTP.

Effects of a memory-enhancing drug on DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor currents and synaptic transmission in hippocampus

The benzoylpiperidine drug BDP-12 (1-(quinoxalin-6-ylcarbonyl)piperidine) enhances the encoding of transient and stable forms of memory by rats. Results reported here show that the drug increases fast, excitatory (glutamatergic) synaptic responses in hippocampal slices by about 50% with an EC50 of 170 microM. Analyses with polysynaptic responses indicated that the drug has a facilitatory action at concentrations as low as 12.5 microM. BDP-12 at 1 mM did not change the resting membrane potential, input resistance or spiking threshold and it did not alter monosynaptic potentials mediated by gamma-aminobutyric acid (GABA) receptors; it did, however, enhance disynaptic inhibitory responses. In membrane patches excised from hippocampal neurons, BDP-12 at moderate concentrations (50 microM) increased the steady-state currents mediated by DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and slowed the rate at which the receptors desensitize, with a much larger effect on the former; the drug delayed the closing of the AMPA receptor channel after 1-msec agonist pulses. BDP-12 had no detectable effect on [3H]AMPA binding affinity. A related and more potent analog produced a different pattern of results in that it had about equal effects on steady-state currents and desensitization rates and significantly increased binding to AMPA receptors. These results indicate that the benzoylpiperidine family of modulators has functionally distinct subclasses. The findings also establish that BDP-12: 1) enhances synaptic responses in the same concentration range at which it alters AMPA receptor kinetics, 2) has a lower apparent threshold for effects on complex network operations than on monosynaptic transmission, 3) does not directly influence inhibitory responses and 4) is likely to modulate AMPA receptors on interneurons as well as on pyramidal neurons.

Spectroscopic determination of cytochrome c oxidase content in tissues containing myoglobin or hemoglobin

A simple spectroscopic method for determining the cytochrome c oxidase, cytochrome a, a3, content in tissue and mitochondria samples independent of myoglobin or blood contamination is described. Using tissue homogenates solubilized in Triton X-100, this assay relies on the selective reduction of mitochondrial cytochromes by the action of potassium cyanide. Monitoring the optical absorbance of these samples at 605 nm provided a quantitative determination of cytochrome c oxidase content in the presence of myoglobin or blood. The cytochrome c oxidase content of porcine heart mitochondria and whole tissue was determined to be 0.85 nmol/mg protein and 30.5 nmol/g wet wt, respectively.

Roles of Cl- channels and Ca2+ mobilization in stretch-induced increase of SA node pacemaker activity

Ionic mechanisms underlying the enhancement of cardiac pacemaking activity by mechanical stretch were investigated in the isolated rabbit sinoatrial (SA) node. A 5-s stretch of 0.2-2.0 g was applied to small tissue strips (1.5 mm x 3.0 mm) of the SA node using a mechanical stimulator. Spontaneous excitation cycle length (SPCL) was monitored by recording endocardial surface potential through modified bipolar electrodes with high-gain amplification. Influence of neurotransmitters released from nerve terminals was eliminated by atropine and propranolol. A stretch > 0.2 g caused a significant shortening of SPCL; there was a positive correlation between the force and the maximum shortening of SPCL. Treatment of the preparation with gadolinium (10 microM) or glibenclamide (1 microM) did not affect the force-response relationship. The positive chronotropic response to mechanical stretch > 0.5 g was reduced significantly by treatment with 4,4'-dinitrostilbene-2,2'-disulfonic acid (5mM), 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (1 mM), or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (50 microM). The positive chronotropic response was also reduced in a low-Ca2+ (0.36 mM) medium and by bath application of ryanodine (0.1 microM) or thapsigargin (2 microM). These findings suggest the possible involvement of mechanosensitive Cl- channels and intracellular Ca2+ mobilization in the stretch-induced enhancement of pacemaking activity in the mammalian SA node, although other conceivable mechanisms cannot be ruled out.

Response to repetitive stimulation of AMPA receptors in patches excised from fields CA1 and CA3 of the hippocampus

Patches excised from fields CA1 and CA3 of the hippocampus were used to study AMPA receptor responses to repetitive application of brief pulses of agonist. AMPA receptors in field CA1 exhibited a larger degree of paired-pulse depression and a slower recovery rate from desensitization than those from CA3 patches. Responses became progressively smaller during a train of short pulses (4 at 100 Hz), an effect that was greater in CA1 than CA3 patches and that was blocked by a drug (cyclothiazide) that slows desensitization. Cyclothiazide also increased steady state currents during a long pulse of glutamate and had a lower EC50 for CA3 than CA1 AMPA receptors. These results suggest (i) that differences in the relative balance of flip vs. flop subunits affect the kinetic and pharmacological properties of AMPA receptors in vivo, and (ii) that the rate of recovery from desensitization may influence responses to the bursts of afferent activity commonly used to induce long-term potentiation.

Effect of cyclothiazide on binding properties of AMPA-type glutamate receptors: lack of competition between cyclothiazide and GYKI 52466

The effects of cyclothiazide on the properties of (R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors were studied using equilibrium binding techniques and interactions with other compounds known to modulate the receptors. Cyclothiazide caused a reduction in [3H]AMPA binding in assays carried out in the presence of thiocyanate, a chaotropic ion that markedly increases the affinity of AMPA receptors and accelerates their desensitization. In the absence of thiocyanate, however, cyclothiazide had no reliable effect on the binding of [3H]AMPA or on the affinity for this agonist assessed from the displacement of [3H]CNQX. The interaction of cyclothiazide with the receptor appears not to be changed by the presence of thiocyanate. Analysis of the results with a kinetic model of the AMPA receptor suggests that cyclothiazide does not block receptor desensitization by making the desensitized state inaccessible but rather by stabilizing the active state, i.e., by increasing the affinity of the latter to a point where it becomes energetically more favorable than the desensitized state. GYKI 52466, an atypical benzodiazepine that blocks AMPA receptor-gated currents, did not reverse the changes in binding affinity produced by cyclothiazide in the presence of thiocyanate. Physiological experiments conducted in excised patches collected from hippocampal pyramidal cells indicated that thiocyanate does not block access of GYKI 52466 to AMPA receptors. These results point to the conclusion that cyclothiazide acts at a site on the AMPA receptor different from that for GYKI 52466.

Differences in the refractory properties of two distinct inhibitory circuitries in field CA1 of the hippocampus

Extracellular reflections of IPSPs were examined in two distinct circuitries in field CA1 of the hippocampus. Stimulation in the stratum radiatum in the presence of AMPA receptor antagonists elicited positive potentials in the same stratum that were eliminated by picrotoxin, a blocker of GABAA receptors. Laminar profile analysis revealed that the response was maximal in the stratum radiatum at a point well distal to the pyramidal cell body layer and had a negative reflection in the stratum oriens. These field IPSPs presumably mediate the feedforward inhibition normally activated by the Schaffer-commissural projections to field CA1. Stimulation of the alveus produced an antidromic response followed by a much slower positive potential in recordings collected in the pyramidal cell layer. The latter response was suppressed by AMPA receptor antagonists or picrotoxin, as expected for disynaptic, recurrent (feedback) inhibition. The laminar profile for the feedback field IPSPs had its maximum near the pyramidal cell layer and its negative dipole in the stratum radiatum. Feedforward IPSPs were inhibited by about 50% if they were preceded within 200 ms by a priming pulse while feedback IPSPs were reduced by less than 20% under comparable conditions. The refractory effect was minimally dependent on stimulation intensity but was strongly affected by an antagonist of GABAB receptors. Attempts to modify IPSPs in the s. radiatum with long trains of low frequency stimulation or with theta-burst stimulation were not successful, suggesting that GABAergic synapses do not have the plasticities found in their glutamatergic counterparts. These results indicate that interneurons contacted by the extrinsic afferents of hippocampus form GABAergic synapses that differ in terms of spatial location and functional properties from the synapses generated by interneurons innervated by the recurrent collaterals of the pyramidal cells. The findings also suggest that repetitive afferent activity, while reducing the influence of dendritic IPSPs on excitatory input, will leave feedback suppression of cell spiking largely intact.

Proteolysis of spectrin by calpain accompanies theta-burst stimulation in cultured hippocampal slices

Tests were carried out to determine if repetitive bursts of afferent stimulation activate calpain, a calcium-dependent protease hypothesized to be involved in the production of long-term potentiation. Antibodies against a stable breakdown product that results from proteolysis of spectrin by calpain were used to identify sites of enzyme activation in cultured hippocampal slices. Slices in which theta-burst stimulation was applied to the Schaffer collateral fibers had pronounced accumulations of breakdown product that were restricted to field CA1, the zone innervated by the stimulated axons. Labelling occurred in the form of scattered puncta and was also present in dendritic processes. The extent of these effects was correlated (r = 0.73) with the amount of theta-burst stimulation delivered. Control slices or those receiving low frequency stimulation had variable, but uniformly lower, amounts of breakdown product and were clearly distinguishable from those given theta bursts. Statistical analyses using a six point rating scheme confirmed this point (P < 0.001). These results satisfy an essential prediction of the hypothesis that calpain plays an important role in the induction of long-term potentiation.

Ionic basis of the chronotropic effect of acetylcholine on the rabbit sinoatrial node

OBJECTIVE

The aim was to study the ionic basis of the chronotropic effects of bath applied acetylcholine and vagal stimulation on the rabbit sinoatrial node.

METHODS

The chronotropic effect of bath applied acetylcholine was measured in single cells and small multicellular preparations from the rabbit sinoatrial node and the chronotropic effect of postganglionic vagal stimulation was measured in the intact sinoatrial node. The roles of the hyperpolarisation activated current, i(f), the acetylcholine activated potassium current, iK,ACh, and the L-type calcium current, iCa, were investigated by blocking the currents with 1-2 mM Cs+ or 10(-6) M UL-FS49, 0.2-1.0 mM Ba2+, and 6 x 10(-6) M nifedipine, respectively.

RESULTS

Under control conditions, small multicellular preparations were approximately two orders of magnitude less sensitive to bath applied acetylcholine than single cells. However, after block of acetylcholinesterase by eserine in small multicellular preparations the sensitivities of the two types of preparation were approximately the same. Block of i(f) either had no discernible effect or increased the chronotropic effect of bath applied acetylcholine on single cells or small multicellular preparations, whereas partial block of iK,ACh reduced it substantially. Similarly, block of i(f) did not suppress the initial slowing of spontaneous action potentials by vagal stimulation, whereas partial block of iK,ACh reduced it. The hyperpolarisation of the arrested sinoatrial node in response to vagal stimulation was also substantially reduced by block of iK,ACh. Partial block of iCa caused large decreases in the action potential amplitude and maximum diastolic potential, but little decrease in the rate of spontaneous action potentials, and therefore did not mimic the effect of acetylcholine.

CONCLUSIONS

The chronotropic effects of bath applied acetylcholine and vagal stimulation are not principally the result of a suppression of i(f) or iCa, whereas the activation of iK,ACh may play an important role.

Effect of thiocyanate on AMPA receptor mediated responses in excised patches and hippocampal slices

The binding affinity of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors for [3H]AMPA is increased 10-30-fold by the chaotropic anion thiocyanate. The present experiments tested if thiocyanate alters AMPA receptor mediated current fluxes and if any such effects are reflected in the waveform of synaptic responses. Currents were measured after a step application of glutamate or AMPA to patches excised from pyramidal cells of hippocampal slice cultures. Application of 1 mM AMPA produced responses with an average peak amplitude of 86 pA at -50 mV and a 10-90% rise time of 1.7 +/- 0.1 ms; the responses desensitized to a steady-state level below 10% of the peak current with a time constant of 11.1 +/- 0.7 ms. Glutamate in presence of D-amino-phosphonopentanoate produced similar responses which were inhibited by 6-cyano-7-nitro-quinoxaline-dione and enhanced by aniracetam or cyclothiazide and thus are characteristic for AMPA receptors. Thiocyanate accelerated the decay of AMPA responses two-fold and reduced the peak current by 30-50% with an EC50 of 3.2 mM which is comparable to its EC50 for enhancing binding. Effects on the desensitization of glutamate induced responses were much smaller and only evident at the highest thiocyanate concentration; no effect was seen on response amplitude. Binding and physiological effects can be adequately explained by assuming that thiocyanate enhances conversion from the sensitive to the desensitized state of the receptor and reduces ligand dissociation from the desensitized state. Synaptic responses were measured in disinhibited hippocampal slices. Perfusion with 20 mM sodium thiocyanate increased the slope of the field excitatory postsynaptic potential by 44.9 +/- 4.2% and reduced its decay time by 10.4 +/- 4.3%. The former effect appears to result at least in part from an increase in transmitter release since it was accompanied by a decrease in paired-pulse facilitation and was reduced in magnitude after enhancing transmitter release. The decrease in the decay time constant points to an effect of thiocyanate on AMPA receptors in situ which is similar to that seen in excised patches. These results demonstrate that an increase in binding affinity may be indicative of reduced rather than enhanced current flow through AMPA receptors. In addition, the results provide further evidence that the kinetics of the AMPA receptor channel contribute significantly to at least the decay phase of fast excitatory synaptic responses.

Cloning and characterization of cDNAs for 70-kDa heat-shock proteins (Hsp70) from two fish species of the genus Oryzias

cDNA corresponding to two hsp70-related genes (OLHSC70 and CEHSC70) were isolated from two lines of cultured fish cells derived from the genus Oryzias. OLHSC70 was 2,261 bp in length and encoded a protein of 686 amino acids with a predicted molecular mass of 76,120 daltons. CEHSC70 was 2,114 bp in length and it lacked the 5' region found in OLHSC70. Two-dimensional electrophoresis revealed that Oryzias latipes has at least three heat-inducible proteins with molecular masses of about 70,000 daltons. One of these proteins (Hsp70.1) was barely expressed under normal conditions but its high-level expression was induced by hyperthermia. The other two proteins (Hsc70.1, and Hsc70.2) were constitutively expressed under normal conditions and only slightly enhanced levels were induced by hyperthermia. Transfection with the cloned sequence, RNA dot-blot analysis and the two-dimensional electrophoresis of proteins showed that OLHSC70 encoded Hsc70.1.

Relationship between the induction of proteins in the HSP70 family and thermosensitivity in two species of Oryzias (Pisces)

A cultured fish cell line, CE, derived from Oryzias celebensis, which lives in a tropical zone, was more heat-resistant than the OL32, which were derived from the Japanese medaka, Oryzias latipes which lives in a temperate zone. Protein synthesis in OL32 cells was also more heat-sensitive than that in CE cells. The relative levels in proteins of the HSP70 family and the ability of cells to tolerate severe heat treatment after a conditioning heat treatment were examined. Twenty-four hours after conditioning heat treatment, both cell lines retained thermotolerance even though three proteins in the HSP70 family had returned to their control levels.

Glycosaminoglycans inhibit degradation of insulin-like growth factor-binding protein-5

Human dermal fibroblasts secrete insulin-like growth factor-binding protein-3 (IGFBP-3), -4, and -5. Fibroblast-conditioned medium contains minimal intact IGFBP-5, and this form of IGFBP is predominantely a 23-kilodalton fragment, suggesting that the IGFBP-5 fragment is derived from intact IGFBP-5 by proteolysis. In this study we investigated the effects of glycosaminoglycans on IGFBP-5 degradation in fibroblast-conditioned medium. The addition of heparin, heparan sulfate, and dermatan sulfate (100 micrograms/ml) to the medium of fibroblast monolayer cultures inhibited IGFBP-5 degradation, as determined by the conversion of intact IGFBP-5 to a 23-kilodalton fragment. In contrast, hyaluronic acid, keratan sulfate, and chondroitin sulfate-A and -C had no effect. Heparin and heparan sulfate inhibited IGFBP-5 degradation at concentrations of 1 or 2.5 micrograms/ml, but 100 micrograms/ml dermatan sulfate were required. Heparin was also inhibitory in vitro, that is when conditioned medium and heparin were incubated without cells. Experiments with modified forms of heparin showed that O-sulfate groups in the 2 or 3 carbon position were required for heparin to be inhibitory. Completely desulfated heparin had no activity, and N-resulfation of desulfated heparin had only a minimal effect. Dextran sulfate, pentosan polysulfate, and fucoidan, which are composed of different saccharide units but contain O-sulfate groups in the 2 or 3 carbon positions, also inhibited IGFBP-5 degradation. These results demonstrate that heparin-like molecules are important regulators of IGFBP-5 degradation. O-Sulfation of the 2 or 3 position of the saccharide ring is required for inhibitory activity. As glycosaminoglycan side-chains are present in proteoglycans that are present in extracellular matrix and on cell surfaces, these side-chains represent a potential mechanism for regulating IGFBP-5 proteolysis in vivo.

A new enzyme, maltobionate alpha-D-glucohydrolase, from alkalophilic Bacillus sp. N-1053

A new enzyme, maltobionate alpha-D-glucohydrolase, was purified to apparent homogeneity from a cell-free extract of alkalophilic Bacillus sp. N-1053 about 930-fold with a yield of 18% and some of its properties were investigated. The enzyme showed optimum activity at about pH 7.0, and was stable over the range of pH 6.0-9.5. The molecular weight was estimated to be 152,000 and 71,000 by HPLC gel filtration on TSKgel G3000SWXL and SDS-polyacrylamide gel electrophoresis, respectively. The enzyme hydrolyzed maltobionate more effectively than disaccharides such as maltose and maltitol or trisaccharides such as maltotrionate, maltotriose and maltotriitol, but showed no activity toward polysaccharides such as amylose, amylopectin and soluble starch. The reaction products from 1 mol of maltobionate were found to be 1 mol of beta-D-glucose and 1 mol of D-gluconate. The Km value for maltobionate was 1.63 mM and the Vmax/Km value for maltobionate was the largest among the substrates tested. The enzyme activity was almost completely inhibited by Hg2+, Ag+, iodine and N-bromosuccinimide, and also inhibited by p-nitrophenyl alpha-D-glucoside, maltose and maltitol.

A centrally active drug that modulates AMPA receptor gated currents

Systemic administration of the drug 1-(1,3-benzodioxol-5-ylcarbonyl)-piperidine (1-BCP) has been reported to enhance monosynaptic responses in the hippocampus in vivo and to improve spatial and olfactory memory in rats. The drug's mechanism of action was investigated in the present study using membrane patches excised from cultured hippocampal slices. The decay time of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor mediated inward currents was greatly increased by 1-BCP in a concentration dependent and reversible fashion; peak current was also enhanced but to a lesser degree. In vitro slice experiments indicated that the drug has parallel effects on the field EPSP. It is concluded that 1-BCP is a centrally active modulator of the AMPA receptor.

Stimulation of NMDA receptors activates calpain in cultured hippocampal slices

The hypothesis that intense stimulation of NMDA receptors activates calpain was tested in long-term cultures of hippocampus. Slices prepared from 10-day-old rats were maintained for periods of up to 6 weeks and then assayed for a stable breakdown product that results from the proteolysis of spectrin by calpain. The breakdown product increased dramatically during the first 24 h after tissue preparation and then decreased to a low level that remained unchanged for weeks. NMDA caused a 2- to 3-fold increase in breakdown product that rose linearly with time (5-30 min) and was blocked by the receptor antagonist MK-801. The effect of NMDA was the same throughout the culture period and was dependent upon the concentration of extracellular calcium with no effect at 2 mM and maximal effect at 4 mM calcium. These results indicate that rapid activation of calpain occurs in undamaged hippocampal neurons following stimulation of NMDA receptors.

Origins of the variations in long-term potentiation between synapses in the basal versus apical dendrites of hippocampal neurons

Responses to theta pattern stimulation, and the long-term potentiation (LTP) they induce, were compared in the basal versus apical dendrites of neurons in field CA1 of hippocampus. A series of 10 theta bursts produced more than twice as much LTP in basal synapses as in their apical counterparts as measured with field EPSPs. This confirms earlier field potential studies showing that the maximum degree of potentiation (the LTP ceiling) is considerably greater in stratum oriens than stratum radiatum. Experiments with whole-cell clamp recording obtained similar results, indicating that synapses at different loci on the same neuron reach different LTP ceilings following prolonged theta burst stimulation. The basal synapses also required fewer theta bursts to reach their LTP ceiling than did the apical synapses. Tests with paired-pulse facilitation and an antagonist of the NMDA receptor gave no indication that the greater LTP in basal synapses was qualitatively different from the lesser effect obtained in apical contacts. Intracellular recording revealed significant differences between basal versus apical responses to single theta bursts and trains of bursts: the within-burst depolarization was greater and the between-burst hyperpolarization was smaller for the basal dendritic responses. These two variables have previously been proposed to influence the magnitude of LTP and the observed differences between basal versus apical synapses are in accord with this hypothesis. Together with recently described immunocytochemical results, the findings reported here suggest that variations in LTP across dendritic subfields of hippocampus reflect a differential distribution of a subclass of GABAergic interneurons.

Molecular cloning of the breakpoint for 3q27 translocation in B-cell lymphomas and leukemias

Reciprocal exchanges between chromosomal region 3q27 and three loci of the Ig genes have been reported in cases of B-cell type non-Hodgkin's lymphoma. We have cloned a region containing a breakpoint junction of 3q27 from a cell line established from a patient with Burkitt's lymphoma carrying t(3;22)(q27;q11). The region cloned was shown to contain an Ig lambda light chain gene fused to a gene on chromosome 3q27. This finding was subsequently confirmed by fluorescence in situ hybridization. Extra nucleotides were present at the joining site. The heptamer-like and nonamer-like sequences separated by an intervening 24 bp were present in the region corresponding to the breakpoint of 3q27, suggesting that a misrecombination in Ig gene rearrangement may be involved in the translocation. Southern blot analysis with a 3q27-specific probe showed rearrangements in three additional patients with B-cell malignancies with the t(3;14)(q27;q32). The breakpoints of all four cases clustered within a limited 3-kb region on chromosome 3q27. The region of 3q27 involved in the translocation was designated as the BCL5 locus. The transcripts from the BCL5 locus were detected in normal tissues and hematopoietic cell lines, and the increased expression of transcript of aberrant size was detected in the established cell line carrying t(3;22). These observations suggest that a gene located at 3q27 is involved in the translocation and that its deregulation plays a role in the malignant transformation of B cells.