Asymptotic behaviour of a semilinear elliptic system with a large exponent

Consider the problem \begin{eqnarray*} -\Delta u &=& v^{\frac 2{N-2}},\quad v>0\quad {in}\quad \Omega, -\Delta v &=& u^{p},\:\:\:\quad u>0\quad {in}\quad \Omega, u&=&v\:\:=\:\:0 \quad {on}\quad \partial \Omega, \end{eqnarray*} where $\Omega$ is a bounded convex domain in $\R^N,$ $N>2,$ with smooth boundary $\partial \Omega.$ We study the asymptotic behaviour of the least energy solutions of this system as $p\to \infty.$ We show that the solution remain bounded for $p$ large and have one or two peaks away form the boundary. When one peak occurs we characterize its location.Comment: 16 pages, submmited for publicatio

Muscle fiber conduction velocity is more affected after eccentric than concentric exercise

It has been shown that mean muscle fiber conduction velocity (CV) can be acutely impaired after eccentric exercise. However, it is not known whether this applies to other exercise modes. Therefore, the purpose of this experiment was to compare the effects of eccentric and concentric exercises on CV, and amplitude and frequency content of surface electromyography (sEMG) signals up to 24 h post-exercise. Multichannel sEMG signals were recorded from biceps brachii muscle of the exercised arm during isometric maximal voluntary contraction (MVC) and electrically evoked contractions induced by motor-point stimulation before, immediately after and 2 h after maximal eccentric (ECC group, N = 12) and concentric (CON group, N = 12) elbow flexor exercises. Isometric MVC decreased in CON by 21.7 ± 12.0% (± SD, p < 0.01) and by 30.0 ± 17.7% (p < 0.001) in ECC immediately post-exercise when compared to baseline. At 2 h post-exercise, ECC showed a reduction in isometric MVC by 24.7 ± 13.7% (p < 0.01) when compared to baseline, while no significant reduction (by 8.0 ± 17.0%, ns) was observed in CON. Similarly, reduction in CV was observed only in ECC both during the isometric MVC (from baseline of 4.16 ± 0.3 to 3.43 ± 0.4 m/s, p < 0.001) and the electrically evoked contractions (from baseline of 4.33 ± 0.4 to 3.82 ± 0.3 m/s, p < 0.001). In conclusion, eccentric exercise can induce a greater and more prolonged reduction in muscle force production capability and CV than concentric exercis

The β(1a) subunit is essential for the assembly of dihydropyridine-receptor arrays in skeletal muscle

Homozygous zebrafish of the mutant relaxed (red(ts25)) are paralyzed and die within days after hatching. A significant reduction of intramembrane charge movements and the lack of depolarization-induced but not caffeine-induced Ca(2+) transients suggested a defect in the skeletal muscle dihydropyridine receptor (DHPR). Sequencing of DHPR cDNAs indicated that the α(1S) subunit is normal, whereas the β(1a) subunit harbors a single point mutation resulting in a premature stop. Quantitative RT-PCR revealed that the mutated gene is transcribed, but Western blot analysis and immunocytochemistry demonstrated the complete loss of the β(1a) protein in mutant muscle. Thus, the immotile zebrafish relaxed is a β(1a)-null mutant. Interestingly, immunocytochemistry showed correct triad targeting of the α(1S) subunit in the absence of β(1a). Freeze-fracture analysis of the DHPR clusters in relaxed myotubes revealed an ≈2-fold reduction in cluster size with a normal density of DHPR particles within the clusters. Most importantly, DHPR particles in the junctional membranes of the immotile zebrafish mutant relaxed entirely lacked the normal arrangement in arrays of tetrads. Thus, our data indicate that the lack of the β(1a) subunit does not prevent triad targeting of the DHPR α(1S) subunit but precludes the skeletal muscle-specific arrangement of DHPR particles opposite the ryanodine receptor (RyR1). This defect properly explains the complete deficiency of skeletal muscle excitation-contraction coupling in β(1)-null model organisms

SRP-27 is a novel component of the supramolecular signaling complex involved in skeletal muscle excitation-contraction coupling.

SRP-27 is a newly identified integral membrane protein constituent of the skeletal muscle sarcoplasmic reticulum We identified its primary structure from cDNA clones isolated from a mouse skeletal muscle cDNA library. ESTs of SRP-27 were found mainly in cDNA libraries from excitable tissues of mouse. Western blot analysis confirmed the expression of SRP-27 in skeletal muscle and to a lower extent in heart and brain. Mild trypsin proteolysis combined with primary structure prediction analysis, suggest that SRP-27 has 4 transmembrane spanning alfa helices and its COOH-terminal domain faces the cytoplasmic side of the endo(sarco)plasmic reticulum. The expression of SRP-27 is higher in fast twitch skeletal muscles compared to slow twitch muscles and peaks during the first month of post-natal development. High resolution immunohistochemistry and western blot analysis of subcellular fractions indicate that SRP-27 is distributed in both longitudinal tubules and in terminal cisternae of the sarcoplasmic reticulum, as well as in the perinuclear membrane systems and the nuclear envelope of myotubes and adult fibers. SRP-27 co-sediments with the ryanodine receptor macromolecular complex in high salt sucrose gradient centrifugation, is pulled-down by anti-ryanodine receptor antibodies as well as by maurocalcin, a well characterized ryanodine receptor modulator. Our data indicate that SRP-27 is part of a sarcoplasmic reticulum supramolecular complex suggesting the involvement of SRP-27 in the structural organization or function of the molecular machinery underlying excitation-contraction coupling