The mitochondrial presequence translocase: an essential role of Tim50 in directing preproteins to the import channel

Mitochondrial proteins with N-terminal targeting signals are transported across the inner membrane via the presequence translocase, which consists of membrane-integrated channel proteins and the matrix Hsp70 import motor. It has not been known how preproteins are directed to the import channel. We have identified the essential protein Tim50, which exposes its major domain to the intermembrane space. Tim50 interacts with preproteins in transit and directs them to the channel protein Tim23. Inactivation of Tim50 strongly inhibits the import of preproteins with a classical matrix-targeting signal, while preproteins carrying an additional inner membrane-sorting signal do not strictly depend on Tim50. Thus, Tim50 is crucial for guiding the precursors of matrix proteins to their insertion site in the inner membrane.     

The Salton Sea as critical habitat to migratory and resident waterbirds

Concern about the Salton Sea ecosystem, based on potential impacts of increasing salinity, contaminants, disease outbreaks, and large die-offs of birds, is heightened because of tremendous prior loss and degradation of wetland habitat in western North America. In 1999, we used a variety of survey methods to describe patterns of abundance of birds at the Salton Sea and in adjacent habitats. Our results further documented the great importance of the Salton Sea within the Pacific Flyway to wintering, migratory, and breeding waterbirds. Exclusive of Eared Grebes, we estimated about 187000 individual waterbirds at the Salton Sea in January, 88000 in April, 170000 in August, and 261000 in November. Additional surveys of Eared Grebes in November and December suggested the total population of all waterbirds was about 434000 to 583000 in those months, respectively. We also documented breeding by about 14000 pairs of colonial waterbirds. Waterbirds were particularly concentrated along the northern, southwestern, southern, and southeastern shorelines and river deltas. By contrast, some species of wading birds (Cattle Egret, White-faced Ibis, Sandhill Crane) and shorebirds (Mountain Plover, Whimbrel, Long-billed Curlew) were much more numerous in agricultural fields of the Imperial Valley than in wetland habitats at the Sea. Various studies indicate the Salton Sea is of regional or national importance to pelicans and cormorants, wading birds, waterfowl, shorebirds, and gulls and terns. Important taxa are the Eared Grebe, American White Pelican, Double-crested Cormorant, Cattle Egret, White-faced Ibis, Ruddy Duck, Yuma Clapper Rail, Snowy Plover, Mountain Plover, Gull-billed, Caspian, and Black terns, and Black Skimmer. Proposed restoration projects should be carefully assessed to ensure they do not have unintended impacts and are not placed where large numbers of breeding, roosting, or foraging birds concentrate. Similarly, plans to enhance opportunities for recreation or commerce at the Sea should aim to avoid or minimize disturbance to birds. Future research should focus on filling gaps in knowledge needed to effectively conserve birds at the Salton Sea.     

Differential control of vesicle priming and short-term plasticity by Munc13 isoforms

Presynaptic short-term plasticity is an important adaptive mechanism regulating synaptic transmitter release at varying action potential frequencies. However, the underlying molecular mechanisms are unknown. We examined genetically defined and functionally unique axonal subpopulations of synapses in excitatory hippocampal neurons that utilize either Munc13-1 or Munc13-2 as synaptic vesicle priming factor. In contrast to Munc13-1-dependent synapses, Munc13-2-driven synapses show pronounced and transient augmentation of synaptic amplitudes following high-frequency stimulation. This augmentation is caused by a Ca(2+)-dependent increase in release probability and releasable vesicle pool size, and requires phospholipase C activity. Thus, differential expression of Munc13 isoforms at individual synapses represents a general mechanism that controls short-term plasticity and contributes to the heterogeneity of synaptic information coding.     

Dynamic effects of predators on cyclic voles: field experimentation and model extrapolation

Mechanisms generating the well-known 3-5 year cyclic fluctuations in densities of northern small rodents (voles and lemmings) have remained an ecological puzzle for decades. The hypothesis that these fluctuations are caused by delayed density-dependent impacts of predators was tested by replicated field experimentation in western Finland. We reduced densities of all main mammalian and avian predators through a 3 year vole cycle and compared vole abundances between four reduction and four control areas (each 2.5-3 km(2)). The reduction of predator densities increased the autumn density of voles fourfold in the low phase, accelerated the increase twofold, increased the autumn density of voles twofold in the peak phase, and retarded the initiation of decline of the vole cycle. Extrapolating these experimental results to their expected long-term dynamic effects through a demographic model produces changes from regular multiannual cycles to annual fluctuations with declining densities of specialist predators. This supports the findings of the field experiment and is in agreement with the predation hypothesis. We conclude that predators may indeed generate the cyclic population fluctuations of voles observed in northern Europe.     

Overexpression of the Shb SH2 domain-protein in insulin-producing cells leads to altered signaling through the IRS-1 and IRS-2 proteins

BACKGROUND: Overexpression of the Src homology 2 domain protein Shb in beta-cells of transgenic mice has been shown to promote an increased beta-cell mass. To investigate the mechanisms by which Shb controls the beta-cell mass, we have presently studied the effects of Shb overexpression on the IRS-1-induced signaling pathway in mouse islet beta-cells and in insulin-producing RINm5F cells and correlated these effects to growth and death patterns. MATERIALS AND METHODS: Shb overexpression was achieved in RINm5F cells by selection of stable clones or by FACS purification of transiently transfected cells. For Shb overexpression in primary mouse islet cells, a Shb-transgene mouse was used. Cell proliferation and death rates were determined using flow cytometry. Serum-, insulin-, and IGF-1-stimulated signaling events were studied by immunoblot, immunoprecipitation, and in vitro kinase procedures. RESULTS: Transient Shb overexpression in RINm5F cells resulted in increased proliferation. Both Shb-overexpressing RINm5F cells and islet cells from transgenic mice (islet Shb) exhibited increased basal tyrosine phosphorylation of IRS-1. Shb overexpression resulted also in the assembly and activation of a multiunit complex consisting of at least Shb, IRS-1, IRS-2, FAK, and PI3K. Consequently, the phosphorylation of Akt was enhanced under basal conditions in Shb overexpressing cells. Finally, Shb overexpression did not affect insulin-induced phosphorylation of the PI3K-antagonist PTEN. CONCLUSION: It is concluded that the Shb-induced alterations in the IRS-1/PI3K/Akt pathway may be relevant to the understanding of growth and death patterns of insulin-producing cells.     

Copper,zinc, and selenium in human blood and urine after injection of sodium 2,3-dimercaptopropane-1-sulfonate: a study on subjects with dental amalgam

This study investigated the effects of a single dose of intravenously administered sodium 2,3-dimercaptopropane-1-sulfonate (DMPS) on the essential elements copper, zinc, and selenium in human blood and urine. The possible role of dental amalgam was also addressed. Eighty individuals, divided in four groups according to the presence or absence of dental amalgam fillings and symptoms self-related to such fillings, were given DMPS (2 mg/kg body wt) and 500 mL Ringer’s acetate intravenously. Urine and blood were collected prior to the injection, and thereafter at intervals over a 24-h period. Cu, Zn, and Se concentrations were determined by atomic absorption spectrometry methods. A statistically significant increase in the concentrations of Cu and Zn in urine was observed 30 and 120 min after the DMPS injection compared to the preinjection concentrations. The concentrations of Se were not affected. The cumulated excretion over 24 h after DMPS injection constitutes only from 0.1% to 0.7% of the body content of these elements. There was no effect of different amalgam statuses on Cu and Zn excretion. We found a temporary decrease (4–7%) in the concentrations of Cu, Zn, and Se in blood 15 and 30 min after DMPS, but this seems to be the result of dilution factors. Administration of a single dose of DMPS does not affect the body stores of the essential elements Cu, Zn, and Se.     

Glibenclamide inhibits islet carnitine palmitoyltransferase 1 activity,leading to PKC-dependent insulin exocytosis

Hypoglycemic sulfonylureas such as glibenclamide have been widely used to treat type 2 diabetic patients for 40 yr, but controversy remains about their mode of action. The widely held view is that they promote rapid insulin exocytosis by binding to and blocking pancreatic beta-cell ATP-dependent K+ (KATP) channels in the plasma membrane. This event stimulates Ca2+ influx and sets in motion the exocytotic release of insulin. However, recent reports show that >90% of glibenclamide-binding sites are localized intracellularly and that the drug can stimulate insulin release independently of changes in KATP channels and cytoplasmic free Ca2+. Also, glibenclamide specifically and progressively accumulates in islets in association with secretory granules and mitochondria and causes long-lasting insulin secretion. It has been proposed that nutrient insulin secretagogues stimulate insulin release by increasing formation of malonyl-CoA, which, by blocking carnitine palmitoyltransferase 1 (CPT-1), switches fatty acid (FA) catabolism to synthesis of PKC-activating lipids. We show that glibenclamide dose-dependently inhibits beta-cell CPT-1 activity, consequently suppressing FA oxidation to the same extent as glucose in cultured fetal rat islets. This is associated with enhanced diacylglycerol (DAG) formation, PKC activation, and KATP-independent glibenclamide-stimulated insulin exocytosis. The fat oxidation inhibitor etomoxir stimulated KATP-independent insulin secretion to the same extent as glibenclamide, and the action of both drugs was not additive. We propose a mechanism in which inhibition of CPT-1 activity by glibenclamide switches beta-cell FA metabolism to DAG synthesis and subsequent PKC-dependent and KATP-independent insulin exocytosis. We suggest that chronic CPT inhibition, through the progressive islet accumulation of glibenclamide, may explain the prolonged stimulation of insulin secretion in some diabetic patients even after drug removal that contributes to the sustained hypoglycemia of the sulfonylurea.     

Humic substances in drinking water and the epidemiology of thyroid disease

Thyroid diseases are common in all populations but the type and frequency depends on environmental factors. In Denmark geographical differences in iodine intake are caused by different iodine contents of drinking water, which varies from < 1 to 139 microg iodine per litre. Comparative epidemiologic studies have demonstrated considerable differences in type and occurrence of thyroid disease with more goitre and hyperthyroidism in Aalborg with water iodine content around 5 microg/L, and more hypothyroidism in Copenhagen with water iodine around 20 microg/L. In Denmark, iodine in ground water is bound in humic substances, which have probably leached from marine sediments in the aquifers. Interestingly, humic substances in water from other parts of the world have goitrogenic properties, especially humic substances from coal and shale. Humic substances are heterogeneous mixtures of naturally occurring molecules, produced by decomposition of plant and animal tissues. The effect of humic substances in drinking water on the epidemiology of thyroid disease probably depends on the source of aquifer sediments.     

Isolation and Identification of the Microbiota of Danish Farmhouse and Industrially Produced Surface-Ripened Cheeses

For studying the microbiota of four Danish surface-ripened cheeses produced at three farmhouses and one industrial dairy, both a culture-dependent and culture-independent approach were used. After dereplication of the initial set of 433 isolates by (GTG)5-PCR fingerprinting, 217 bacterial and 25 yeast isolates were identified by sequencing of the 16S rRNA gene or the D1/D2 domain of the 26S rRNA gene, respectively. At the end of ripening, the cheese core microbiota of the farmhouse cheeses consisted of the mesophilic lactic acid bacteria (LAB) starter cultures Lactococcus lactis subsp. lactis and Leuconostoc mesenteorides as well as non-starter LAB including different Lactobacillus spp. The cheese from the industrial dairy was almost exclusively dominated by Lb. paracasei. The surface bacterial microbiota of all four cheeses were dominated by Corynebacterium spp. and/or Brachybacterium spp. Brevibacterium spp. was found to be subdominant compared to other bacteria on the farmhouse cheeses, and no Brevibacterium spp. was found on the cheese from the industrial dairy, even though B. linens was used as surface-ripening culture. Moreover, Gram-negative bacteria identified as Alcalignes faecalis and Proteus vulgaris were found on one of the farmhouse cheeses. The surface yeast microbiota consisted primarily of one dominating species for each cheese. For the farmhouse cheeses, the dominant yeast species were Yarrowia lipolytica, Geotrichum spp. and Debaryomyces hansenii, respectively, and for the cheese from the industrial dairy, D. hansenii was the dominant yeast species. Additionally, denaturing gradient gel electrophoresis (DGGE) analysis revealed that Streptococcus thermophilus was present in the farmhouse raw milk cheese analysed in this study. Furthermore, DGGE bands corresponding to Vagococcus carniphilus, Psychrobacter spp. and Lb. curvatus on the cheese surfaces indicated that these bacterial species may play a role in cheese ripening.     

Spatio-temporal processing of surface EMG signals from the sternocleidomastoideus muscle to assess effects of radiotherapy on motor unit conduction velocity and firing rate—A pilot study

Radiation therapy causes both muscle and nerve tissue damage. However, the evolution and mechanisms of these damages are not fully understood. Information on the state of active muscle fibres and motoneurons can be obtained by measuring sEMG signals and calculating the conduction velocity (CV) and firing rate of individual motor units, respectively. The aim of this pilot study was to evaluate if the multi-channel surface EMG (sEMG) technique could be applied to the sternocleidomastoideus muscle (SCM) of radiotherapy patients, and to assess if the CV and firing rate are altered as a consequence of the radiation.

Surface EMG signals were recorded from the radiated and healthy SCM muscles of 10 subjects, while subjects performed isometric rotation of the head. CV and firing rate were calculated using two recently proposed methods based on spatio-temporal processing of the sEMG signals. The multi-channel sEMG technique was successfully applied to the SCM muscle and CV and firing rates were obtained. The measurements were fast and simple and comfortable for the patients. Sufficient data quality was obtained from both sides of seven and four subjects for the CV and firing rate analysis, respectively. No differences in CV or firing rate were found between the radiated and non-radiated sides (p = 0.13 and p = 0.20, respectively). Firing rate and CV were also obtained from a myokymic discharge pattern. It was found that the CV decreased significantly (p = 0.01) during the bursts.