SERCA-1 conformational change exerted by the Ca2+-channel blocker diltiazem affects mammalian skeletal muscle function.

In skeletal muscle (SM), inward Ca2+-currents have no apparent role in excitation-contraction coupling (e-c coupling), however the Ca2+-channel blocker can affect twitch and tetanic muscle in mammalian SM. Experiments were conducted to study how diltiazem (DLZ) facilitates e-c coupling and inhibits contraction. 1) In complete Extensor Digitorum Longus (EDL) muscle and single intact fibres, 0.03 mM DLZ causes twitch potentiation and decreases force during tetanic activity, with increased fatigue. 2) In split open fibres isolated from EDL fibres, DLZ inhibits sarcoplasmic reticulum (SR) Ca2+-loading in a dose-dependent manner and has a potentiating effect on caffeine-induced SR Ca2+-release. 3) In isolated light SR (LSR) vesicles, SERCA1 hydrolytic activity is not affected by DLZ up to 0.2 mM. However, ATP-dependent Ca2+-uptake was inhibited in a dose-dependent manner at a concentration where e-c coupling is changed. 4) The passive Ca2+-efflux from LSR was reduced by half with 0.03 mM diltiazem, indicating that SR leaking does not account for the decreased Ca2+-uptake. 5) The denaturation profile of the SERCA Ca2+-binding domain has lower thermal stability in the presence of DLZ in a concentration-dependent manner, having no effect on the nucleotide-binding domain. We conclude that the effect of DLZ on SM is exerted by crossing the sarcolemma and interacting directly with the SERCA Ca2+-binding domain, affecting SR Ca2+-loading during relaxation, which has a consequence on SM contractility. Diltiazem effect on SM could be utilized as a tool to understand SM e-c coupling and muscle fatigue.

Longitudinal large-scale changes in maternal circulating microRNAs associated with gestation-related compartments, fetal sex, and growth during and post-pregnancy.

Circulating microRNAs (c-miRNAs) during pregnancy could provide information regarding the functional status of the mother and fetus. However, it remains unclear which pregnancy-related processes are actually reflected by changes c-miRNAs. Here, we used large-scale c-miRNA profiling of maternal plasma during and post-pregnancy, and compared it with that of non-pregnant women. Fetal growth measurements and fetal sex data were used to identify associated changes in these transcripts. Surprisingly, c-miRNA subpopulations with prominent expression in maternal/fetal compartments (placenta, amniotic fluid, umbilical cord plasma and breast milk) were found to be under-expressed in circulation throughout pregnancy relative to non-pregnant plasma profiles. Furthermore, we found a bias in global c-miRNA expression in association with fetal sex right from the first trimester, in addition to a specific c-miRNA signature of fetal growth. Our results demonstrate the existence of specific temporal changes in c-miRNA populations associated with specific pregnancy-related compartments and processes, including fetal sex, and growth.

Skeletal muscle: from birth to old age, routes to mechanical and metabolic failure. / Músculo esquelético: del nacimiento a la vejez, rutas hacia la falla mecánica y metabólica.

Skeletal muscle (SM) is the most abundant tissue and the largest reservoir of protein in the body. It transports glucose in an insulin dependent manner by the glucose transporter type 4 (GLUT4) and contributes in the maintenance of serum amino acids concentration. By its mass and energetic requirements, it is fundamental for the systemic metabolic balance. In the present work, we present the effect of gestational undernourishment (GU) on the mechanical and metabolic properties of SM at birth and in old age in an animal model. Mechanical studies were performed on isolated muscles, while the GLUT4, amino acid transporters LAT2, SNAT2 and insulin receptors (IR) determination were performed on isolated transverse-tubule membranes (TT). The GU in offspring at birth, results in low muscle mass with increased contraction force and resistance to fatigue. However, in two-years old rats, there was muscle hypotrophy and sarcopenia, the force decreased between 50 and 70% in control rats and rats with GU respectively, accompanied by a lower expression of LAT2, SNAT2 and IR in TT. In conclusion, GU irreversibly affects the SM, an effect that could be similar in humans, which help us to understand the events that associate the GU with the metabolic debacle of SM and the metabolic diseases of human adulthood.