Cytoskeleton, L-type Ca2+ and stretch activated channels in injured skeletal muscle

The extra-sarcomeric cytoskeleton (actin microfilaments and anchoring proteins) is involved in maintaining the sarco-membrane stiffness and integrity and in turn the mechanical stability and function of the intra- and sub-sarcoplasmic proteins. Accordingly, it regulates Ca2+ entry through the L-type Ca2+ channels and the mechano-sensitivity of the stretch activated channels (SACs). Moreover, being intra-sarcomeric cytoskeleton bound to costameric proteins and other proteins of the sarcoplasma by intermediate filaments, as desmin, it integrates the properties of the sarcolemma with the skeletal muscle fibres contraction. The aim of this research was to compare the cytoskeleton, SACs and the ECC alterations in two different types of injured skeletal muscle fibres: by muscle denervation and mechanical overload (eccentric contraction). Experiments on denervation were made in isolated Soleus muscle of male Wistar rats; forced eccentric-contraction (EC) injury was achieved in Extensor Digitorum Longus muscles of Swiss mice. The method employed conventional intracellular recording with microelectrodes inserted in a single fibre of an isolated skeletal muscle bundle. The state of cytoskeleton was evaluated by recording SAC currents and by evaluating the resting membrane potential (RMP) value determined in current-clamp mode. The results demonstrated that in both injured skeletal muscle conditions the functionality of L-type Ca2+ current, ICa, was affected. In parallel, muscle fibres showed an increase of the resting membrane permeability and of the SAC current. These issues, together with a more depolarized RMP are an index of altered cytoskeleton. In conclusion, we found a symilar alteration of ICa, SAC and cytoskeleton in both injured skeletal muscle conditions

Excitation-contraction coupling and mechano-sensitivity in denervated skeletal muscles

Skeletal muscle atrophy can be defined as a wasting or decrease in muscle mass and muscle force generation owing lack of use, ageing, injury or disease. Thus, the etiology of atrophy can be different. Atrophy in denervated muscle is a consequence of two factors: 1) the complete lack of motoneuron activity inducing the deficiency of neurotransmitter release and 2) the muscles disuse. The balance of the muscular functions depends on extra- and intra-muscular signals. In the balance are involved the excitation-contraction coupling (ECC), local growth factors, Ca2+-dependent and independent intracellular signals, mechano-sensitivity and mechano-transduction that activate Ca2+-dependent signaling proteins and cytoskeleton- nucleus pathways to the nucleus, that regulate the gene expression. Moreover, retrograde signal from intracellular compartments and cytoskeleton to the sarcolemma are additional factors that regulate the muscle function. Proteolytic systems that operate in atrophic muscles progressively reduce the muscle protein content and so the sarcolemma, ECC and the force generation. In this review we will focus on the more relevant changes of the sarcolemma, excitation-contraction coupling, ECC and mechano-transduction evaluated by electrophysiological methods and observed from early- to long-term denervated skeletal muscles. This review put in particular evidence that long-term denervated muscle maintain a sub-population of fibers with ECC and contractile machinery able to be activated, albeit in lesser amounts, by electrical and mechanical stimulation. Accordingly, this provides a potential molecular explanation of the muscle recovery that occurs in response to rehabilitation strategy as transcutaneous electrical stimulation and passive stretching of denervated muscles, which wre developed as a result of empirical clinical observations

Line-shape analysis and simulation of Er3+ photoluminescence spectra in erbium-stabilized nanocrystalline zirconia structures

Peculiarities of the near-infrared and visible up-conversion spectra of nanocrystalline (Er2O3)x (ZrO2)1-x have been studied. It is shown that for the samples with 0.026 < x < 0.143 the photoluminescence spectra of Er3+ are defined a by similar erbium environment in spite of the different symmetry of the host ZrO2 matrix. The low temperature and room temperature emission bands in the spectral range of the 4I13/2 → 4I15/2 transition are measured and interpreted in terms of the multi-electron molecular orbitals cluster model developed for the case of nanocrystal structures. The role of the intra-manifold 4I13/2 relaxatio

Muscular effects of relaxin on the mouse colon: mechanical and electrophysiological studies

Relaxin has been reported to influence gastrointestinal motility in mice. However, at present, nothing is known about the effects of relaxin on the electrophysiological properties of the gastrointestinal smooth muscle. In the present experiments relaxin, other than influencing the colonic motility pattern, has been shown to act on cell membrane properties. The results of the present study indicate that relaxin directly modulates the motility of the proximal colon and the membrane potential of smooth muscle