Architectural specialization of the intrinsic thoracic limb musculature of the American badger (Taxidea taxus)

Evaluation of the relationships between muscle structure and digging function in fossorial species is limited. Badgers and other fossorial specialists are expected to have massive forelimb muscles with long fascicles capable of substantial shortening for high power and applying high out‐force to the substrate. To explore this hypothesis, we quantified muscle architecture in the thoracic limb of the American badger (Taxidea taxus) and estimated the force, power, and joint torque of its intrinsic musculature in relation to the use of scratch‐digging behavior. Architectural properties measured were muscle mass, belly length, fascicle length, pennation angle, and physiological cross‐sectional area. Badgers possess hypertrophied shoulder flexors/humeral retractors, elbow extensors, and digital flexors. The triceps brachii is particularly massive and has long fascicles with little pennation, muscle architecture consistent with substantial shortening capability, and high power. A unique feature of badgers is that, in addition to elbow joint extension, two biarticular heads (long and medial) of the triceps are capable of applying high torques to the shoulder joint to facilitate retraction of the forelimb throughout the power stroke. The massive and complex digital flexors show relatively greater pennation and shorter fascicle lengths than the triceps brachii, as well as compartmentalization of muscle heads to accentuate both force production and range of shortening during flexion of the carpus and digits. Muscles of most functional groups exhibit some degree of specialization for high force production and are important for stabilizing the shoulder, elbow, and carpal joints against high limb forces generated during powerful digging motions. Overall, our findings support the hypothesis and indicate that forelimb muscle architecture is consistent with specializations for scratch‐digging. Quantified muscle properties in the American badger serve as a comparator to evaluate the range of diversity in muscle structure and contractile function that exists in mammals specialized for fossorial habits. J. Morphol. 2013. © 2012 Wiley Periodicals, Inc.     

Electron Microscopic Evidence in Support of α-Solenoid Models of Proteasomal Subunits Rpn1 and Rpn2

Rpn1 (109 kDa) and Rpn2 (104 kDa) are components of the 19S regulatory complex of the proteasome. The central portions of both proteins are predicted to have toroidal α-solenoid folds composed of 9-11 proteasome/cyclosome repeats, each ∼ 40 residues long and containing two α-helices and turns [A. V. Kajava, J. Biol. Chem. 277, 49791-49798, 2002]. To evaluate this prediction, we examined the full-length yeast proteins and truncated versions thereof consisting only of the repeat-containing regions by gel filtration, CD spectroscopy, and negative-staining electron microscopy (EM). All four proteins are monomeric in solution and highly α-helical, particularly the truncated ones. The EM data were analyzed by image classification and averaging techniques. The preponderant projections, in each case, show near-annular molecules 6-7 nm in diameter. Comparison of the full-length with the truncated proteins showed molecules similar in size and shape, indicating that their terminal regions are flexible and thus smeared to invisibility in the averaged images. We tested the toroidal model further by calculating resolution-limited projections and comparing them with the EM images. The results support the α-solenoid model, except that they indicate that the repeats are organized not as symmetrical circular toroids but in less regular horseshoe-like structures.     

Comparison of 60-Hz electric fields and incandescent light as aversive stimuli controlling the behavior of rats

Rats were exposed to two procedures which enabled them to press a lever to turn off a 90 or 100 kV/m 60-Hz electric field or, later in the study, illumination from an incandescent lamp. Under one procedure, a response turned off the stimulus for a fixed duration, after which the stimulus was turned on again. A response during the off-period restarted the fixed duration. None of the rats turned the field off reliably. Next, under an alternative procedure, pressing one lever turned the field off; pressing the other lever turned it back on; responding under those conditions differed little from that seen at 0 kV/m. Under both procedures, when illumination from an incandescent lamp served as the stimulus, each rat did turn the stimulus off, and performances varied with stimulus intensity. The results show that a 100 kV/m 60-Hz electric field is not sufficient to function as an aversive stimulus under two procedures where illumination from a lamp does function as an aversive stimulus.     

Possible existence of ion pairs at the mouths of ion channels

An electrostatic calculation suggests that when an ion is bound near the mouth of a channel penetrating a low-dielectric membrane, a counter ion may form an ion pair with this ion. The tendency towards ion-pair formation is remarkably enhanced at channel mouths by forces (image forces) arising from the charges induced on the boundaries between different dielectrics. The binding constant for the formation of ion-pairs of monovalent ions is estimated under the assumption that local interactions between the counter ion and the channel wall are negligibly small. It is of the order of 1–10 molal^?1 or more for the binding of a Cl^? (F^?) counter ion to an $\text{Na}{}^{\mathrm{+}}$ ($\text{Li}{}^{\mathrm{+}}$) ion if appropriate conditions are fulfilled. The binding constant depends on the position of the binding site, the dimensions and geometries of the channel and channel mouth, and the state of ion loading of the channel, as well as the ionic species. The present results also indicate that when cation (anion) channels have anionic (cationic) groups as integrant parts of their channel walls, interactions between these charged groups and permeant ions are markedly enhanced by the image forces.     

Implications for cytoplasmic pH,protonmotice force,and amino-acid transport across the plasmalemma of Riccia fluitans

By means of pH-sensitive microelectrodes, cytoplasmic pH has been monitored continuously during amino-acid transport across the plasmalemma of Riccia fluitans rhizoid cells under various experimental conditions. (i) Contrary to the general assumption that import of amino acids (or hexoses) together with protons should lead to cytoplasmic acidification, an alkalinization of 0.1–0.3 pH_c units was found for all amino acids tested. Similar alkalinizations were recorded in the presence of hexoses and methylamine. No alkalinization occurred when the substrates were added in the depolarized state or in the presence of cyanide, where the electrogenic H⁺-pump is inhibited. (ii) After acidification of the cytoplasm by means of various concentrations of acetic acid, amino-acid transport is massively altered, although the protonmotive force remained essentially constant. It is suggested that H⁺-cotransport is energetically interconnected with the proton-export pump which is stimulated by the amino-acid-induced depolarization, thus causing proton depletion of the cytoplasm. It is concluded that, in order to investigate H⁺-dependent cotransport processes, the cytoplasmic pH must be measured and be under continuous experimental control; secondly, neither pH nor the protonmotive force across a membrane are reliable quantities for analysing a proton-dependent process.Abbreviations 3-OMG 3-oxymethylglucose - pH_c cytoplasmic pH - _m electrical potential difference across the respective membrane, i.e. membrane potential - _H+/F (=pmf) electrochemical proton gradient     

Secondary transport of amino acids by membrane vesicles derived from lactic acid bacteria

Lactococci are fastidious bacteria which require an external source of amino acids and many other nutrients. These compounds have to pass the membrane. However, detailed analysis of transport processes in membrane vesicles has been hampered by the lack of a suitable protonmotive force (pmf)-generating system in these model systems. A membrane-fusion procedure has been developed by which pmf-generating systems can be functionally incorporated into the bacterial membrane. This improved model system has been used to analyze the properties of amino acid transport systems in lactococci. Detailed studies have been made of the specificity and kinetics of amino acid transport and also of the interaction of the transport systems with their lipid environment. The properties of a pmf-independent, arginine-catabolism specific transport system in lactococci will be discussed.Abbreviations pmf protonmotive force - transmembrane electrical potential - pH transmembrane pH gradient - PE phosphatidylethanolamine - PC phosphatidylcholine Paper adapted from a treatise Secondary Transport of Amino Acids by Membrane Vesicles Derived from Lactic Acid Bacteria and awarded the Kluyver Prize 1988 by the Netherlands Society of Microbiology.     

Chronic exposure to ELF fields may induce depression

Exposure to extremely-low-frequency (ELF) electric or magnetic fields has been postulated as a potentially contributing factor in depression. Epidemiologic studies have yielded positive correlations between magnetic- and/or electric-field strengths in local environments and the incidence of depression-related suicide. Chronic exposure to ELF electric or magnetic fields can disrupt normal circadian rhythms in rat pineal serotonin-N-acetyltransferase activity as well as in serotonin and melatonin concentrations. Such disruptions in the circadian rhythmicity of pineal melatonin secretion have been associated with certain depressive disorders in human beings. In the rat, ELF fields may interfere with tonic aspects of neuronal input to the pineal gland, giving rise to what may be termed "functional pinealectomy." If long-term exposure to ELF fields causes pineal dysfunction in human beings as it does in the rat, such dysfunction may contribute to the onset of depression or may exacerbate existing depressive disorders.     

Protonmotive force in freshwater sulfate-reducing bacteria,and its role in sulfate accumulation in Desulfobulbus propionicus

The protonmotive force in several sulfate-reducing bacteria has been determined by means of radiolabelled membrane-permeant probes (tetraphenyl-phosphonium cation, TPP⁺, for , and benzoate for pH). In six of ten freshwater strains tested only the pH gradient could be determine, while the membrane potential was not accessible due to nonspecific binding of TPP⁺. The protonmotive force of the other four strains was between –110 and –155 mV, composed of a membrane potential of –80 to –140 mV and a pH gradient between 0.25 and 0.8 (inside alkaline) at pH_out=7. In Desulfobulbus propionicus the pH gradient decreased with rising external pH values. This decrease, however, was compensated by an increasing membrane potential. Sulfate, which can be highly accumulated by the cells, did not affect the protonmotive force, if added in concentrations of up to 4 mM. The highest sulfate accumulation observed (2500-fold), which occurred at external sulfate concentrations below 5 M, could be explained by a symport of three protons per sulfate, if equilibrium with the protonmotive force was assumed. At higher sulfate concentrations the accumulation decreased and suggested an electroneutral symport of two protons per sulfate. At sulfate concentrations above 500 M, the cells stopped sulfate uptake before reaching an equilibrium with the protonmotive force.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - MOPS morpholinopropanesulfonic acid - TPP⁺ tetraphenylphosphonium cation - EDTA ethylenediaminetetraacetic acid - pH transmembrane pH gradient (pH_in-pH_out) - transmembrane electrical potential difference     

Detection of native-like models for amino acid sequences of unknown three-dimensional structure in a data base of known protein conformations.

We present an approach which can be used to identify native-like folds in a data base of protein conformations in the absence of any sequence homology to proteins in the data base. The method is based on a knowledge-based force field derived from a set of known protein conformations. A given sequence is mounted on all conformations in the data base and the associated energies are calculated. Using several conformations and sequences from the globin family we show that the native conformation is identified correctly. In fact the resolution of the force field is high enough to discriminate between a native fold and several closely related conformations. We then apply the procedure to several globins of known sequence but unknown three dimensional structure. The homology of these sequences to globins of known structures in the data base ranges from 49 to 17%. With one exception we find that for all globin sequences one of the known globin folds is identified as the most favorable conformation. These results are obtained using a force field derived from a data base devoid of globins of known structure. We briefly discuss useful applications in protein structural research and future development of our approach.