Influence of barium on rectification in rat neocortical neurons

The effect of low concentrations of barium on the membrane properties of rat neocortical neurons was studied in vitro. Potassium currents were examined using single-electrode current- and voltage-clamp techniques. Neurons responded to bath application of barium (10–100 μM) with a membrane depolarization associated with an increase in input resistance. Under voltage clamp conditions, an inward shift in holding current was observed. The effects of barium were rapidly reversible upon washing and persisted in the presence of TTX. The equilibrium potential for the barium-induced inward current was near −110 mV, suggesting that barium inhibited a tonically active potassium conductance. Measurements of current voltage relationships indicated an inward rectification of this conductance between −50 and −130 mV. These results provide strong evidence that barium blocks a persistent potassium ‘leak’ current in neocortical neurons that contributes to the resting potential of these cells

A low-voltage activated, transient calcium current is responsible for the time-dependent depolarizing inward rectification of rat neocortical neurons in vitro

Intracellular recordings were obtained from rat neocortical neurons in vitro. The current-voltage-relationship of the neuronal membrane was investigated using current- and single-electrode-voltage-clamp techniques. Within the potential range up to 25 mV positive to the resting membrane potential (RMP: –75 to –80 mV) the steady state slope resistance increased with depolarization (i.e. steady state inward rectification in depolarizing direction). Replacement of extracellular NaCl with an equimolar amount of choline chloride resulted in the conversion of the steady state inward rectification to an outward rectification, suggesting the presence of a voltage-dependent, persistent sodium current which generated the steady state inward rectification of these neurons. Intracellularly injected outward current pulses with just subthreshold intensities elicited a transient depolarizing potential which invariably triggered the first action potential upon an increase in current strength. Single-electrode-voltage-clamp measurements reveled that this depolarizing potential was produced by a transient calcium current activated at membrane potentials 15–20 mV positive to the RMP and that this current was responsible for the time-dependent increase in the magnitude of the inward rectification in depolarizing direction in rat neocortical neurons. It may be that, together with the persistent sodium current, this calcium current regulates the excitability of these neurons via the adjustment of the action potential threshold

Are Annulate Lamellae in the Drosophila Embryo the Result of Overproduction of Nuclear Pore Components?

Annulate lamellae are cytoplasmic organelles composed of stacked sheets of membrane containing pores that are structurally indistinguishable from nuclear pores. The functions of annulate lamellae are not well understood . Although they may be found in virtually any eucaryotic cell, they occur most commonly in transformed and embryonic tissues . In Drosophila, annulate lamellae are found in the syncytial blastoderm embryo as it is cleaved to form the cellular blastoderm . The cytological events of the cellularization process are well documented, and may be used as temporal landmarks when studying changes in annulate lamellae . By using morphometric techniques to analyze electron micrographs of embryos, we are able to calculate the number of pores per nucleus in nuclear envelopes and annulate lamellae during progressive stages of cellularization . We find that annulate lamellae pores remain at a low level while nuclear envelopes are expanding and acquiring pores in early interphase . Once nuclear envelopes are saturated with pores, however, the number of annulate lamellae pores increases more than 10-fold in 9 min . Over the next 30 min it gradually declines to the initial low level . On the basis of these results, we propose (a) that pore synthesis and assembly continues after nuclear envelopes have been saturated with pores; (b) that these supernumerary pores accumulate transiently in cytoplasmic annulate lamellae; and (c) that because these pores are not needed by the embryo they are subsequently degraded

Association of DRG1 and DRG2 with Ribosomes from Pea, Arabidopsis and Yeast

DRGs are highly conserved GTP binding proteins.All eukaryotes examined contain DRG1 and DRG2 orthologs. The first experimental evidence for GTP binding by a plant DRG1 protein and by DRG2 from any organism is presented. DRG1 antibodies recognized a single ~43-kDa band in plant tissues, whereas DRG2 antibodies recognized ~45-,43-,and 30-kDa bands.An in vitro transcription and translation assay suggested that the 45-kDa band represents full-length DRG2 and that the smaller bands are specific proteolytic products. Homogenates from pea roots and root apices were used to produce fractions enriched in cytosolic and microsomal monosomes and polysomes. DRG1 and the 45- and 43-kDa DRG2 bands occurred in the cytosol and associated with cytosolic monosomes.I n contrast,the 30-kDa form of DRG2 was strongly enriched in polysome fractions.Thus,DRG1and the larger forms of DRG2 may be involved in translational initiation, and the 30-kDa form of DRG2 may be involved in translational elongation.DRG1 and the 45-and43-kDa forms of DRG2 can reassociate with ribosomes in vitro, a process that is partially inhibited by GTP-y-S Cells expressing FLAG-tagged ribosomal proteins from transgenic lines of Arabidopsis and yeast also demonstrated DRG-ribosome interactions

Adynamia episodica hereditaria with myotonia: A non-inactivating sodium current and the effect of extracellular pH

To study the mechanism of periodic paralysis, we investigated the properties of intact muscle fibers biopsied from a patient who had adynamia episodica hereditaria with electromyographic signs of myotonia. When the potassium concentration in the extracellular medium, [K]e, was 3.5 mmol/l, force of contraction, membrane resting potential, and intracellular sodium activity were normal, but depolarizing voltage clamp steps revealed the existence of an abnormal inward current. This current was activated at membrane potentials less negative than -80 mV, reached a maximum within 50 msec, and was not inactivated with time. The inward current was completely and reversibly blocked by tetrodotoxin, which indicates that it was carried by sodium ions. In a solution containing 9 mmol/l potassium, normal muscle would depolarize to -63 mV and yet be capable of developing full tetanic force upon stimulation. The muscle from the patient depolarized to -57 mV and became inexcitable, i.e., it was paralyzed. A contracture did not develop. Lowering of the extracellular pH did not influence the resting potential, but it effectively antagonized or prevented the paralytic effect of high [K]e by changing the inactivation characteristics of the sodium channels. Hydrochlorothiazide, which had a therapeutic effect on the patient, did not prevent paralysis in vitro. An abnormal rise of the intracellular sodium activity was recorded when the extracellular potassium concentration was raised to 10 mmol/l

Comprehensive analysis of the cork oak (Quercus suber) transcriptome involved in the regulation of bud sprouting

Cork oaks show a high capacity of bud sprouting as a response to injury, which is important for species survival when dealing with external factors, such as drought or fires. The characterization of the cork oak transcriptome involved in the different stages of bud sprouting is essential to understanding the mechanisms involved in these processes. In this study, the transcriptional profile of different stages of bud sprouting, namely (1) dormant bud and (2) bud swollen, vs. (3) red bud and (4) open bud, was analyzed in trees growing under natural conditions. The transcriptome analysis indicated the involvement of genes related with energy production (linking the TCA (tricarboxylic acid) cycle and the electron transport system), hormonal regulation, water status, and synthesis of polysaccharides. These results pinpoint the different mechanisms involved in the early and later stages of bud sprouting. Furthermore, some genes, which are involved in bud development and conserved between species, were also identified at the transcriptional level. This study provides the first set of results that will be useful for the discovery of genes related with the mechanisms regulating bud sprouting in cork oakinfo:eu-repo/semantics/publishedVersio

Update on the management of Lennox-Gastaut syndrome with a focus on rufinamide

Carl E StafstromSection of Pediatric Neurology, Departments of Neurology and Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, USAObjective: This review summarizes the treatment of Lennox-Gastaut syndrome, an intractable epileptic encephalopathy of early childhood. In particular, the review focuses on rufinamide, a recently released anticonvulsant medication with reported effectiveness in this epilepsy syndrome.Methods: A systematic literature search (PubMed) was performed to review the existing literature pertaining to the treatment of Lennox-Gastaut syndrome as well as studies involving rufinamide as an anticonvulsant medication.Results: The published literature to date documents a beneficial effect of rufinamide on children over 4 years old with Lennox-Gastaut syndrome. Studies indicate a significant decrease in tonic and atonic seizure frequency as well as total seizure frequency compared to placebo-treated children. Rufinamide appears to be well tolerated and a safe medication, somnolence and vomiting being the most common side effects.Conclusions: Rufinamide is a promising adjunctive therapy for Lennox-Gastaut syndrome, an intractable childhood epilepsy. To ensure its optimal effectiveness, clinicians must be familiar with the medication’s clinical response profile and potential for adverse effects.Keywords: pediatric, epilepsy, epileptic encephalopathy, Lennox-Gastaut syndrome, rufinamid

Expression Patterns of Arabidopsis DRG Genes: Promoter-GUS Fusions, Quantitative RT-PCR and Patterns of Protein Accumulation in Response to Environmental Stresses

DRGs are very highly conserved GTP-binding proteins. All eukaryotes contain DRG1 and DRG2 orthologs. Arabidopsis has three DRGs: AtDRG1 (At4g39520), AtDRG2 (At1g17470), and AtDRG3 (At1g72660). DRG2 and DRG3 encode proteins that are 95% identical; identity between DRG1 and DRG2/3 is 55%. The focus of this article is expression of Arabidopsis DRGs. DRG1 and DRG2 promoter-GUS constructs showed similar spatial expression in seedlings and mature organs, but gene-specific differences were noted. Quantitative real-time PCR experiments indicated similar levels of DRG1 and DRG2 mRNA accumulation in most tissues. DRG3 transcripts were very low in all tissues. Heat stress at 37 C led to a 10-fold increase in DRG1 transcripts and a 1000-fold increase in DRG3 transcripts. DRG1 antibodies recognized a 43-kD protein, and DRG2 antibodies recognized bands at 30, 43, and 45 kD. Plants were exposed to stresses (salt, heat, cold, UV light, osmotic, and other stresses) and examined by Western blotting. Only heat stress caused detectable changes. Heat did not affect DRG1, but DRG2 and a 72-kD protein recognized by DRG2 antibodies both increased. The modest changes in DRG mRNA and protein levels seen here suggest that other types of regulation, such as altered subcellular localization, may be important for their cellular functions