A TEA-insensitive flickering potassium channel active around the resting potential in myelinated nerve

A novel potassium-selective channel which is active at membrane potentials between -100 mV and +40 mV has been identified in peripheral myelinated axons of Xenopus laevis using the patch-clamp technique. At negative potentials with 105 mM-K on both sides of the membrane, the channel at 1 kHz resolution showed a series of brief openings and closings interrupted by longer closings, resulting in a flickery bursting activity. Measurements with resolution up to 10 kHz revealed a single-channel conductance of 49 pS with 105 mM-K and 17 pS with 2.5 mM-K on the outer side of the membrane. The channel was selective for K ions over Na ions (PNa/PK = 0.033). The probability of being within a burst in outside-out patches varied from patch to patch (> 0.2, but often > 0.9), and was independent of membrane potential. Open-time histograms were satisfactorily described with a single exponential (tau o = 0.09 msec), closed times with the sum of three exponentials (tau c = 0.13, 5.9, and 36.6 msec). Sensitivity to external tetraethylammonium was comparatively low (IC50 = 19.0 mM). External Cs ions reduced the apparent unitary conductance for inward currents at Em = -90 mV (IC50 = 1.1 mM). Ba and, more potently, Zn ions lowered not only the apparent single-channel conductance but also open probability. The local anesthetic bupivacaine with high potency reduced probability of being within a burst (IC50 = 165 nM). The flickering K channel is clearly different from the other five types of K channels identified so far in the same preparation. We suggest that this channel may form the molecular basis of the resting potential in vertebrate myelinated axons.     

Vegetation types and patterns in Senegal based on multivariate analysis of field and NOAA-AVHRR satellite data

Abstract. Woody vegetation was studied in 44 sites in Senegal. Species composition and density were analysed with TWINSPAN and Canonical Correspondence Analysis; 16 vegetation types were defined. A supervised, multispectral and multitemporal classification of day and night, dry season NOAA-AVHRR imagery was used to identify their distribution with a classification accuracy ranging from 60–100%.     

Effects of antibiotics on synthesis and persistence of sigma E in sporulating Bacillus subtilis.

A potential regulatory link between the activation of a sporulation-specific sigma factor (sigma E) and forespore septum formation was investigated by treating Bacillus subtilis with inhibitors of protein or peptidoglycan synthesis and monitoring the consequences of these treatments on sigma E activation and septation. Western blot (immunoblot) and electron microscopic analyses revealed that both the formation of sigma E and septation were inhibited to a similar degree when either rifampin or chloramphenicol was added at different times before the second hour into sporulation but that penicillin preferentially blocked septation. We interpret these results as indicating that the syntheses of the gene products for both septation and sigma E activation occur at approximately the same time in development but that synthesis of an intact septum is unlikely to be a prerequisite for the formation of sigma E. We observed that penicillin could not only block septation but, depending on the time of its addition, could also inhibit both the activation of sigma E and the synthesis of its precursor. The basis of this effect is unknown, but it is not due to an overall disruption of protein synthesis. The incorporation of [35S] methionine by the sporulating cultures was unaffected by penicillin treatment. A time course study of the effects of rifampin and chloramphenicol treatments on sigma E levels revealed that both the synthesis of sigma E and its disappearance from sporulating cultures is inhibited by these antibiotics. This suggests that ongoing macromolecular synthesis is required for the turnover of sigma E.     

A simple,rapid assay for cysteamine and other thiols

Cysteamine is under investigation as an aid in radiation therapy and as a treatment for the inherited disorder cystinosis. An assay is presented for its measurement in biological fluids. The specific reaction of thiosulfonates with sulfhydryl compounds is employed to form a radiolabeled derivative of cysteamine which is then isolated by high-voltage electrophoresis on paper. Cysteamine can be measured in aqueous solutions, plasma, and urine with this method.     

Isolation and partial characterization of the major apolipoprotein component of bovine serum high density lipoprotein.

The delipidated protein component of bovine serum high density lipoprotein was fractionated by gel filtration on a Sephadex G-150 column (equilibrated with buffer containing 6 M urea) into three fractions: I, II and III. Fractions I and II together constitute 88% of all the protein weight of bovine high density lipoprotein, whereas fraction III accounts for the remaining 12%. Analysis of the fractions by sodium dodecyl sulfate-polyacrylamide electrophoresis reveals that fraction I consists mostly of aggregated forms of fraction II and some higher molecular weight species, probably irreversible aggregates of fraction II. The irreversible aggregates are apparently formed during the delipidation procedure or upon aging of the lipoprotein. The major protein component of the high density bovine lipoprotein is found in fraction II; it has a molecular weight of 27 000 plus or minus 1500 and appears to be homogeneous by several physicochemical criteria. The amino acid composition of fractions I and II are essentially identical; their spectral properties, including absorption, fluorescence, and circular dichroism spectra, are similar; however, fraction I appears to contain traces of oxidized lipid and more secondary alpha-helical organization than fraction II. By comparison with the intact lipoprotein, which contains about 65% of alpha-helical structure, fractions I and II have diminished alpha-helical organization, 55% and 43%, respectively. Fraction III, on sodium dodecyl sulfate-polyacrylamide electrophoresis, separates into two protein bands of equivalent intensity, having molecular weights around 13 000 and 11 000. Fraction III is markedly distinct from the other two, in amino acid composition and spectral properties, especially in its red-shifted fluorescence and very low content of alpha-helical structure. The protein composition of bovine serum high density lipoprotein is compared with recently published results for high density lipoprotein apoproteins of man, chimpanzee, rhesus monkey, pig and rat. Similarities and differences are discussed in terms of possible evolutionary and functional factors.     

White chest in the west: pelage colour and mitochondrial variation in the common hamster (Cricetus cricetus) across Europe

The common hamster (Cricetus cricetus L.), a rodent of the Eurasian steppes and agricultural areas, is threatened by habitat loss. Remnant populations in Western and Central Europe are small, isolated and genetically impoverished. The populations of Belgium, The Netherlands and North Rhine-Westphalia, Germany (BNN), for which Nehring proposed the epiphet canescens, are most affected by this decline. They are distinguished from more eastern populations by large, white areas on throat, chest and forelegs. These traits are sometimes also found in other populations, which casts doubt on their value as diagnostic characteristics. Here, we show that the frequency of occurrence of relatively large chest spots, chin streaks and cuffs on the forelegs is highest in BNN, where a white chest spot occurs in 67–100 % of the sampled individuals, compared to 0–8 % in Central and Eastern European populations. Additionally, hamsters from the Upper Rhine area also display relatively high frequencies of these characters (7–44 %). This suggests a common origin of BNN and Upper Rhine hamsters and an ancient expansion route along the Rhine Valley. A supplementary genetic study of two mitochondrial genes revealed extremely low diversity in both BNN and Upper Rhine hamsters but also clear differentiation and isolation between the two remaining relict populations of North Rhine-Westphalia.     

Expression of connexin 43 mRNA in microisolated murine osteoclasts and regulation of bone resorption in vitro by gap junction inhibitors

Several studies have demonstrated that connexin 43 (Cx43) mediates signals important for osteoblast function and osteogenesis. The role of gap junctional communication in bone resorption is less clear. We have investigated the expression of Cx43 mRNA in osteoclasts and bone resorption cultures and furthermore, the functional importance of gap junctional communication in bone resorption. RT-PCR analysis demonstrated Cx43 mRNA expression in mouse bone marrow cultures and in osteoclasts microisolated from the marrow cultures. Cx43 mRNA was also expressed in bone resorption cultures with osteoclasts and osteoblasts/stromal cells incubated for 48h on devitalized bone slices. An up-regulation of Cx43 mRNA was detected in parathyroid (PTH)-stimulated (0.1 nM) bone resorption. Two inhibitors of gap junction communication, 18alpha-glycyrrhetinic acid (30 microM) and oleamide (100 microM), significantly inhibited PTH- and 1,25-(OH)(2)D(3)-stimulated osteoclastic pit formation. In conclusion, our data indicate a functional role for gap junction communication in bone resorption.