GABA_A-mediated synaptic activity in rat hippocampal neurones <i>in vitro</i> and its modulation by other neurotransmitters and second messengers.

The patch-clamp technique (whole-cell and outside-out configurations) has been used to characterize spontaneous ɣ-aminobutyric acid A (GABAA) receptor mediated currents in pyramidal cells of thin hippocampal slices obtained from neonatal rats. In early postnatal life, GABA is the main excitatory neurotransmitter on hippocampal pyramidal cells. The frequency distribution histogram of spontaneous GABAergic currents could be fitted by a single exponential function revealing the random nature of these events. The present results demonstrate that in tetrodotoxin (TTX) solution spontaneous GABAA receptor mediated miniature postsynaptic currents (mPSCs) were present. At -70 mV the first peak in the current amplitude distribution was 16 ± 6 pA (n =13). This value was similar to that found for GABAergic currents (14 ± 6 pA) elicited by low intensity extracellular stimulation, suggesting that this effect was due to the release of elementary units of GABA. In outside-out patches, GABA activated single-channel events of 24 and 35 pS conductance. Assuming that a postsynaptic current of 15 pA corresponds to a single quantum of GABA, one could calculate that one quantal current represents the simultaneous opening of 6 to 9 GABAA receptor channels in the postsynaptic cell. The metabotropic Glutamate Receptor (mGluR) agonist, 1 -aminocyclopentane-1,3-dicarboxylic acid (t-ACPD), induced an increase in frequency but not in amplitude of spontaneously occurring GABAergic currents; this potentiating effect was blocked by the Protein Kinase A (PKA) antagonist Rp-adenosine 3', 5'-cyclic monophosphotioate triethylamine (Rp-cAMPS), suggesting that glutamate, acting on mGluRs, is able to increase GABA release through the metabolic pathway which involves PKA. The potentiating effect of t-ACPD was not observed in TTX solution indicating that the site of action of the mGluR agonist is probably located at the somatodendritic level and not on the nerve terminals ofGABAergic intemeurones. In the presence of forskolin, which increases intracellular cyclic AMP (cAMP) levels, a rise in frequency but not in amplitude of miniature GABAA receptor mediated currents was observed, an effect that was prevented by the selective PKA antagonist Rp-cAMPS. These experiments suggest that presynaptic mGluRs localized on GABAergic interneurones may facilitate the activity of these cells and their release of GABA through cAMP-dependent PKA. Moreover, PKA may interfere directly with the mechanism of GABA release as demonstrated by its action on miniature events. The present results provide new evidence that the release of a major neurotransmitter such as GABA is up-regulated by another neurotransmitter namely Glutamate, thus demonstrating an important reinforcement of excitatory signals during an early stage of brain development

Improving the regeneration of skeletal muscle

Several pathological conditions of the skeletal muscle (myopathies, dystrophies and age-related atrophy) represent a burden for health care system. Satellite cells are postnatal resident myogenic precursors present in the skeletal muscles throughout the entire lifespan. The identification of novel therapeutic strategies able to enhance their regenerative capacity is one of the most promising tools to compensate muscle degeneration and to restore functional muscle performance in patients and elderly. Our research activity is aiming to contribute to this crucial topic

The microtransplantation technique: a simple ad useful approach to study receptors transplanted into xenopus oocytes

Neuroreceptors are involved in many neurological diseases and represent the preferential target for the pharmacological treatments. Thus functional studies of their activity, by the use of electrophysiological techniques, are a fundament approach to understand not only the pathological mechanism of many neurological diseases but also the mechanism of action of potential drugs. Unfortunately, this cannot be applied for studying the receptor activity in all the human tissues. The option is the use of animal models, however they often resemble only some of the neurological diseases in human. In addition, adult or old animals are not always suitable for electrophysiological studies of age-related diseases. Here, we propose the microtransplantation technique as a novel and useful method to study receptors in humans and, more in general, in adult animals

Epidermal Growth Factor \u2013 based adhesion substrates elicit myoblast scattering, proliferation, differentiation and promote satellite cell myogenic activation

The biochemical properties of muscle extracellular matrix are essential for stem cell adhesion, motility, proliferation and myogenic development. Recombinant elastin-like polypeptides are synthetic polypeptides that, besides maintaining some properties of the native protein, can be tailored by fusing bioactive sequences to their C-terminal. Our laboratory synthesized several Human Elastin-Like Polypeptides (HELP) derived from the sequence of human tropoelastin. Here, we developed a novel HELP family member by fusing the elastin-like backbone to the sequence of human Epidermal Growth Factor. We employed this synthetic protein, named HEGF, either alone or in combination with other proteins of the HELP family carrying RGD-integrin binding sites, as adhesion substrate for C2C12 myoblasts and satellite cells primary cultures. Adhesion of myoblasts to HEGF-based substrates induced scattering, decreased adhesion and cytoskeleton assembly; the concomitant presence of the RGD motifs potentiated all these effects. Recombinant substrates induced myoblasts proliferation, differentiation and the development of multinucleated myotubes, thus favoring myoblasts expansion and preserving their myogenic potential. The effects induced by adhesion substrates were inhibited by AG82 (Tyrphostin 25) and herbimycin A, indicating their dependence on the activation of both the EGF receptor and the tyrosine kinase c-src. Finally, HEGF increased the number of muscle stem cells (satellite cells) derived from isolated muscle fibers in culture, thus highlighting its potential as a novel substrate for skeletal muscle regeneration strategies

Intrinsic ionic conductances mediate the spontaneous electrical activity of cultured mouse myotubes

AbstractMouse skeletal myotubes differentiated in vitro exhibited spontaneous contractions associated with electrical activity. The ionic conductances responsible for the origin and modulation of the spontaneous activity were examined using the whole-cell patch-clamp technique and measuring [Ca2+]i transients with the Ca2+ indicator, fura 2-AM. Regular spontaneous activity was characterized by single TTX-sensitive action potentials, followed by transient increases in [Ca2+]i. Since the bath-application of Cd2+ (300 μM) or Ni2+ (50 μM) abolished the cell firing, T-type (ICa,T) and L-type (ICa,L) Ca2+ currents were investigated in spontaneously contracting myotubes. The low activation threshold (around −60 mV) and the high density of ICa,T observed in contracting myotubes suggested that ICa,T initiated action potential firing, by bringing cells to the firing threshold. The results also suggested that the activity of ICa,L could sustain the [Ca2+]i transients associated with the action potential, leading to the activation of apamin-sensitive SK-type Ca2+-activated K+ channels and the afterhyperpolarization (AHP) following single spikes. In conclusion, an interplay between voltage-dependent inward (Na+ and Ca2+) and outward (SK) conductances is proposed to mediate the spontaneous pacemaker activity in cultured muscle myotubes during the process of myogenesis

A preliminary study on the role of Piezo1 channels in myokine release from cultured mouse myotubes

It has long been known that regular physical exercise induces short and long term benefits reducing the risk of cardiovascular disease, diabetes, osteoporosis, cancer and improves sleep quality, cognitive level, mobility, autonomy in enderly. More recent is the evidence on the endocrine role of the contracting skeletal muscle. Exercise triggers the release of miokines, which act in autocrine, paracrine and endocrine ways controlling the activity of muscles but also of other tissues and organs such as adipose tissue, liver, pancreas, bones, and brain. The mechanism of release is still unclear. Neuromuscular electrical stimulation reproduces the beneficial effects of physical activity producing physiological metabolic, cardiovascular, aerobic responses consistent with those induced by exercise. In vitro, Electrical Pulse Stimulations (EPS) of muscle cells elicit cell contraction and mimic miokine release in the external medium. Here we show that, in cultured mouse myotubes, EPS induce contractile activity and the release of the myokine IL-6. Gadolinium highly reduces EPS-induced IL-6 release, suggesting the involvement of mechanical activated ion channels. The chemical activation of mechanosensitive Piezo1 channels with the specific agonist Yoda1 stimulates IL-6 release similarly to EPS, suggesting the involvement of Piezo1 channels in the control of the myokine release. The expression of Piezo1 protein in myotubes was confirmed by the Western blot analysis. To the best of our knowledge, this is the first evidence of a Piezo1-mediated effect in myokine release and suggests a potential translational use of specific Piezo1 agonists for innovative therapeutic treatments reproducing/enhancing the benefits of exercise mediated by myokines

The State of the Art of Piezo1 Channels in Skeletal Muscle Regeneration

Piezo1 channels are highly mechanically-activated cation channels that can sense and transduce the mechanical stimuli into physiological signals in different tissues including skeletal muscle. In this focused review, we summarize the emerging evidence of Piezo1 channel-mediated effects in the physiology of skeletal muscle, with a particular focus on the role of Piezo1 in controlling myogenic precursor activity and skeletal muscle regeneration and vascularization. The disclosed effects reported by pharmacological activation of Piezo1 channels with the selective agonist Yoda1 indicate a potential impact of Piezo1 channel activity in skeletal muscle regeneration, which is disrupted in various muscular pathological states. All findings reported so far agree with the idea that Piezo1 channels represent a novel, powerful molecular target to develop new therapeutic strategies for preventing or ameliorating skeletal muscle disorders characterized by an impairment of tissue regenerative potential

Tunable FDM 3D printing of flexible poly(butylene adipate terephthalate)-based biocomposite filaments

Poly(butylene adipate-co-terephthalate), PBAT, is a synthetic and 100% biodegradable polymer based on fossil resources, with high elongation at break and high flexibility. These properties are comparable to lowdensity polyethylene, making PBAT a very promising biodegradable material that could replace it in some industrial applications. However, its lower mechanical properties have limited its application range. The reinforcement of PBAT with rigid filler, such as zein-TiO2 (ZTC) complex microparticles, has the purpose to expand its application fields, from the food and agricultural packaging to healthcare sector. The 3D printability of bio-based composites was demonstrated by realizing complex structures with a commercial FDM printer

Flexible PBAT-Based Composite Filaments for Tunable FDM 3D Printing

Biobased composites with peculiar properties offer an attractive route for producing environmentally friendly materials. The reinforcement for poly(butylene adipate-co-terephthalate) (PBAT), based on zein-titanium dioxide (TiO2) complex (ZTC) microparticles, is presented and used to produce composite filaments, successfully 3-dimensionally (3D) printed by fused deposition modeling (FDM). The outcome of ZTC addition, ranging from 5 to 40 wt %, on the thermo-mechanical properties of composite materials was analyzed. Results reveal that storage modulus increased with increasing the ZTC content, leading to a slight increase in the glass transition temperature. The creep compliance varies with the ZTC concentration, denoting a better resistance to deformation under constant stress conditions for composites with higher complex content. Scanning electron microscopy was used to assess the quality of interphase adhesion between PBAT and ZTC, showing good dispersion and distribution of complex microparticles in the polymer matrix. Infrared spectroscopy confirmed the formation of a valid interface due to the formation of hydrogen bonds between filler and polymer matrix. Preliminary tests on the biocompatibility of these materials were also performed, showing no cytotoxic effects on cell viability. Finally, the 3D printability of biobased composites was demonstrated by realizing complex structures with a commercial FDM printer

ADENOSINE AND LOW AFFINITY P1 RECEPTOR-MEDIATED MODULATION OF NACHR CHANNEL ACTIVITY AT THE ENDPLATE REGION OF ADULT MOUSE SKELETAL MUSCLE FIBRES

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