Potential benefits of taurine in the prevention of skeletal muscle impairment induced by disuse in the hindlimb-unloaded rat

Hindlimb unloading (HU) in rats induces severe atrophy and a slow-to-fast phenotype transition in postural slow-twitch muscles, as occurs in human disuse conditions, such as spaceflight or bed rest. In rats, a reduction of soleus muscle weight and a decrease of cross-sectional area (CSA) were observed as signs of atrophy. An increased expression of the fast-isoform of myosin heavy chain (MHC) showed the phenotype transition. In parallel the resting cytosolic calcium concentration (restCa) was decreased and the resting chloride conductance (gCl), which regulates muscle excitability, was increased toward the values of the fast-twitch muscles. Here, we investigated the possible role of taurine, which is known to modulate calcium homeostasis and gCl, in the restoration of muscle impairment due to 14-days-HU. We found elevated taurine content and higher expression of the taurine transporter TauT in the soleus muscle as compared to the fast-twitch extensor digitorum longus (EDL) muscle of control rats. Taurine level was reduced in the HU soleus muscle, although, TauT expression was not modified. Taurine oral supplementation (5?g/kg) fully prevented this loss, and preserved resting gCl and restCa together with the slow MHC phenotype. Taurine supplementation did not prevent the HU-induced drop of muscle weight or fiber CSA, but it restored the expression of MURF-1, an atrophy-related gene, suggesting a possible early protective effect of taurine. In conclusion, taurine prevented the HU-induced phenotypic transition of soleus muscle and might attenuate the atrophic process. These findings argue for the beneficial use of taurine in the treatment of disuse-induced muscle dysfunction.     

Beta amino acid‐modified and fluorescently labelled kisspeptin analogues with potent KISS1R activity

Kisspeptin analogues with improved metabolic stability may represent important ligands in the study of the kisspeptin/KISS1R system and have therapeutic potential. In this paper we assess the activity of known and novel kisspeptin analogues utilising a dual luciferase reporter assay in KISS1R‐transfected HEK293T cells. In general terms the results reflect the outcomes of other assay formats and a number of potent agonists were identified among the analogues, including β²‐hTyr‐modified and fluorescently labelled forms. We also showed, by assaying kisspeptin in the presence of protease inhibitors, that proteolysis of kisspeptin activity within the reporter assay itself may diminish the agonist outputs. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Targeting kidney CLC-K channels: Pharmacological profile in a human cell line versus Xenopus oocytes

CLC-K chloride channels play a crucial role in kidney physiology and genetic mutations, affecting their function are responsible for severe renal salt loss in humans. Thus, compounds that selectively bind to CLC-Ka and/or CLC-Kb channels and modulate their activity may have a significant therapeutic potential. Here, we compare the biophysical and pharmacological behaviors of human CLC-K channels expressed either in HEK293 cells or in Xenopus oocytes and we show that CLC-K channel properties are greatly influenced by the biochemical environment surrounding the channels. Indeed, in HEK293 cells the potentiating effect of niflumic acid (NFA) on CLC-Ka/barttin and CLC-Kb/barttin channels seems to be absent while the blocking efficacy of niflumic acid and benzofuran derivatives observed in oocytes is preserved. The NFA block does not seem to involve the accessory subunit barttin on CLC-K1 channels. In addition, the sensitivity of CLC-Ks to external Ca²⁺ is reduced in HEK293 cells. Based on our findings, we propose that mammalian cell lines are a suitable expression system for the pharmacological profiling of CLC-Ks.     

I–J loop involvement in the pharmacological profile of CLC-K channels expressed in Xenopus oocytes

CLC-K chloride channels and their subunit, barttin, are crucial for renal NaCl reabsorption and for inner ear endolymph production. Mutations in CLC-Kb and barttin cause Bartter syndrome. Here, we identified two adjacent residues, F256 and N257, that when mutated hugely alter in Xenopus oocytes CLC-Ka's biphasic response to niflumic acid, a drug belonging to the fenamate class, with F256A being potentiated 37-fold and N257A being potently blocked with a K_D ~ 1 μM. These residues are localized in the same extracellular I–J loop which harbors a regulatory Ca^2 + binding site. This loop thus can represent an ideal and CLC-K specific target for extracellular ligands able to modulate channel activity. Furthermore, we demonstrated the involvement of the barttin subunit in the NFA potentiation. Indeed the F256A mutation confers onto CLC-K1 a transient potentiation induced by NFA which is found only when CLC-K1/F256A is co-expressed with barttin. Thus, in addition to the role of barttin in targeting and gating, the subunit participates in the pharmacological modulation of CLC-K channels and thus represents a further target for potential drugs.     

Sex determination and sex reversal

Sex determination in mammals is based on a genetic cascade that controls the fate of the gonads. Gonads will then direct the establishment of phenotypic sex through the production of hormones. Different types of sex reversal are expected to occur if mutations disrupt one of the three steps of gonadal differentiation: formation of the gonadal primordia, sex determination, and testis or ovary development.     

A chloroplast system capable of translating heterologous mRNAs

A system capable of incorporating amino acids into protein has been prepared from chloroplasts isolated from spinach leaves. The activity of the system is inhibited by chloramphenicol or RNase but not by rifampycin or cycloheximide. After reducing the endogenous activity by treatment with micrococcal nuclease, the system responds to homologous or heterologous mRNAs. The RNA from MS-2 phage is translated faithfully as demonstrated by the isolation from the translation products of a protein with the same mobility of the phage coat protein. Partial proteolytic digestion confirmed that the protein synthesized in vitro is indeed the phage protein.     

Chloride conductance of denervated gastrocnemius fibers from normal goats

Membrane potentials, cable parameters, and component resting ionic conductances of gastrocnemius fibers from normal goats were measured in vitro at six to 32 days following denervation by section of the tibial nerve. Denervated fibers were depolarized an average of 11.6 ± 1.5 mV (six preparations) from the control mean of 62.1 ± 1.0 mV (124 fibers) over the period studied. Fibrillation, tetrodotoxin-resistant action potentials, and anodebreak excitation were present in the denervated preparations after 13 days. The control cable parameters from 124 fibers (13 preparations) were membrane resistance, 1052 ± 70 ω·cm² and membrane capacitance, 6.2 μF/cm². In denervated fibers membrane resistance increased two to three times in the 13 to 32 day period; membrane capacitance increased about 50% in normal solution at eight to nine, 27–28, and 32 days. Myoplasmic resistivity was assumed to be 112 Ωcm. Measurements were made at 38°C. Component resting conductances were determined from the cable parameters in normal and chloride-free solution. Mean chloride conductance G_Cl and mean potassium conductance G_K of control fibers were 776 ± 49 μmhos/cm² and 175 ± 15 μmhos/cm² (92 fibers), respectively. Following denervation G_Cl increased slightly at six to nine days then fell to low values at 16 to 32 days that were close to or indistinguishable from zero. G_K increased significantly to 372 ± 40 μmhos/cm² and 499 ± 90 μmhos/cm² at 16 to 20 and 32 days, respectively. It was concluded from these findings that G_Cl and G_K of mammalian skeletal muscle are controlled by factors from the nerve and/or muscle action potentials. Goat muscle is different from frog muscle in which G_Cl does not change and G_K decreases during denervation.     

Suppression of lymphocyte stimulation by anterior hypothalamic lesions in the guinea pig

Anterior hypothalamic lesions in the guinea pig inhibited lymphocyte stimulation in whole blood cultures with the antigen tuberculin and with the mitogen phytohemagglutinin (PHA) and suppressed the delayed cutaneous hypersensitivity response to tuberculin. The lesions did not affect the stimulation of purified lymphocytes with either tuberculin or PHA. The anterior hypothalamic lesions had no effect on the absolute number of T and B lymphocytes.     

The gene for X-linked Kallmann syndrome: a human neuronal migration defect.

A new gene from the distal short arm of the human X chromosome has recently been cloned and characterized. Mutations in this gene lead to the neuronal migration defect observed in Kallmann syndrome. Although there is no direct proof for the involvement of this gene in neuronal migration, significant similarities between its predicted protein product and neural adhesion molecules have been found. X-linked Kallmann syndrome represents the first example in vertebrates of a neuronal migration defect for which the gene has been isolated.