An Integrated Biomarker Approach Using Flounder to Improve Chemical Risk Assessments in the Heavily Polluted Seine Estuary

The objective of this study was to develop an integrative approach in ecotoxicology (from biomarkers to population genetics) to assess the ecological status of fish populations. Flounders (Platichthys flesus) collected after the spawning season in the heavily polluted Seine estuary were compared with the moderately polluted Bay of Douarnenez. The muscle energetic reserves were highly depleted in Seine vs. Douarnenez fish. The Seine fish displaying a reduced capacity to manage the oxidative stress and a higher energetic metabolism. An increase in the content of muscle membrane phospholipids (sphingomyelin, phosphatidylserine, free sterols) was detected in the Seine vs. Douarnenez fish. The data integration allowed to hypothesize relationships between membrane phospholipids, xenobiotic metabolism, bioenergetics, and antioxidant defence. The genetic diversity considering neutral markers was maintained in the heavily polluted Seine population compared with the Douarnenez population. Finally, we suggest that the high physiological cost of tolerance to toxicants in the Seine flounder population could compromise its capacity to respond in the future to an additional stressor like warming waters in shallow depth. Thus, this population could be submitted to an ecological risk.

Cardiac activation heat remains inversely dependent on temperature over the range 27–37°C

The relation between heat output and stress production (force per cross-sectional area) of isolated cardiac tissue is a key metric that provides insight into muscle energetic performance. The heat intercept of the relation, termed “activation heat,” reflects the metabolic cost of restoring transmembrane gradients of Na+ and K+ following electrical excitation, and myoplasmic Ca2+ concentration following its release from the sarcoplasmic reticulum. At subphysiological temperatures, activation heat is inversely dependent on temperature. Thus one may presume that activation heat would decrease even further at body temperature. However, this assumption is prima facie inconsistent with a study, using intact hearts, which revealed no apparent change in the combination of activation and basal metabolism between 27 and 37°C. It is thus desired to directly determine the change in activation heat between 27 and 37°C. In this study, we use our recently constructed high-thermal resolution muscle calorimeter to determine the first heat-stress relation of isolated cardiac muscle at 37°C. We compare the relation at 37°C to that at 27°C to examine whether the inverse temperature dependence of activation heat, observed under hypothermic conditions, prevails at body temperature. Our results show that activation heat was reduced (from 3.5 ± 0.3 to 2.3 ± 0.3 kJ/m3) at the higher temperature. This leads us to conclude that activation metabolism continues to decline as temperature is increased from hypothermia to normothermia and allows us to comment on results obtained from the intact heart by previous investigators.

Escape responses by jet propulsion in scallops

The impressive swimming escape response of scallops uses a simple locomotor system that facilitates analysis of the functional relationships between its primary components. One large adductor muscle, two valves, the muscular mantle, and the rubbery hinge ligament are the basic elements allowing swimming by jet propulsion. Although these basic functional elements are shared among scallop species, the exact nature of the escape response varies considerably within and among species. Valve shape and density have opposing influences upon the capacity for swimming and the ease of attack by predators once captured. Patterns of muscle use can partly overcome the constraints imposed by shell characteristics. The depletion of muscle reserves during gametogenesis leads to a trade-off between escape response performance and reproductive investment. However, changes in muscle energetic status influence repeat performance more than initial escape performance. Escape response performance is influenced by habitat temperature and mariculture techniques. During scallop ontogeny, changes in susceptibility to predation and in reproductive investment may influence escape response capacities. These ontogenetic patterns are likely to vary with the longevity and maximal size of each species. Although the basic elements allowing swimming by jet propulsion are common to scallops, their exact use varies considerably among species.

Effects of creatine and vitamin E on muscle energetic metabolism, antioxidant stability and meat quality of pigs

The effects of supplementing the diet of pigs with creatine monohydrate (CMH) and vitamin E on blood plasma creatine concentration, vitamin E level in muscle, muscle energy metabolism, antioxidant capacity and meat (musculus longissimus dorsi) quality of pigs (DNA tested and negative on malignant hyperthermia) were investigated. Two treatments were used: supplementation with CMH alone (2 g.kg−1 of feed, 10 days before slaughter); and supplementation with both vitamin E (500 mg α-tocopherol.kg−1 of feed for minimum of 30 days) and CMH (2 g.kg−1 of feed, 10 days before slaughter). Pigs supplemented with CMH alone showed elevated plasma creatine concentration (P ≤ 0.05). Phosphorus nuclear magnetic resonance (31P NMR) measurements on post mortem (15 min.) muscle samples showed the highest phosphocreatine levels and ratio PCr/Pi (P ≤ 0.05) in CMH supplemented pigs alone and in combination with vitamin E. Dietary supplementation with vitamin E significantly (P ≤ 0.05) increased the concentration of α-tocopherol in meat. Supplementation with CMH alone or in combination with vitamin E resulted in higher (P = 0.07) a values of loin chops at 5 days of storage. Antioxidative capacity (measured as MDA production after incubation of longissimus muscle homogenates with Fe2+/ascorbate) was substantially improved by vitamin E and somewhat by CMH supplementation.

Recovery of microvascular Po2 during the exercise off-transient in muscles of different fiber type

The speed with which muscle energetic status recovers after exercise is dependent on oxidative capacity and vascular O2 pressures. Because vascular control differs between muscles composed of fast- vs. slow-twitch fibers, we explored the possibility that microvascular O2 pressure (PmvO2; proportional to the O2 delivery-to-O2 uptake ratio) would differ during recovery in fast-twitch peroneal (Per: 86% type II) compared with slow-twitch soleus (Sol: 84% type I). Specifically, we hypothesized that, in Per, PmvO2 would be reduced immediately after contractions and would recover more slowly during the off-transient from contractions compared with Sol. The Per and Sol muscles of six female Sprague-Dawley rats (weight = ∼220 g) were studied after the cessation of electrical stimulation (120 s; 1 Hz) to compare the recovery profiles of PmvO2. As hypothesized, PmvO2 was lower throughout recovery in Per compared with Sol (end contraction: 13.4 ± 2.2 vs. 20.2 ± 0.9 Torr; end recovery: 24.0 ± 2.4 vs. 27.4 ± 1.2 Torr, Per vs. Sol; P ≤ 0.05). In addition, the mean response time for recovery was significantly faster for Sol compared with Per (45.1 ± 5.3 vs. 66.3 ± 8.1 s, Sol vs. Per; P < 0.05). Despite these findings, PmvO2 rose progressively in both muscles and at no time fell below end-exercise values. These data indicate that, during the recovery from contractions (which is prolonged in Per), capillary O2 driving pressure (i.e., PmvO2) is reduced in fast-compared with slow-twitch muscle. In conclusion, the results of the present investigation may partially explain the slowed recovery kinetics (phosphocreatine and O2 uptake) found previously in 1) fast- vs. slow-twitch muscle and 2) various patient populations, such as those with congestive heart failure and diabetes mellitus.

Phosphocreatine content of freeze-clamped muscle: influence of creatine kinase inhibition

The study of cellular energetics is critically dependent on accurate measurement of high-energy phosphates. Muscle values of phosphocreatine (PCr) vary greatly between in vivo measurements (i.e., by nuclear magnetic resonance) and chemical measurements determined from muscles isolated and quick-frozen. The source of this difference has not been experimentally identified. A likely cause is activation of ATPases and phosphotransfer from PCr to ADP. Therefore, rat hindlimb skeletal muscle was perfused either with or without 2 mM iodoacetamide, a creatine kinase inhibitor, and muscle was freeze-clamped either at rest or after contraction. Creatine kinase inhibition resulted in ∼6 μmol/g higher PCr and lower creatine in the freeze-clamped soleus, red gastrocnemius, and white gastrocnemius. This PCr content difference was reduced when the initial PCr content was decreased with prior contractions. Therefore, the amount of PCr artifact appears to scale with initial PCr content within a fiber-type section. This artifact directly affects the measurement and, thus, the calculations of muscle energetic parameters from studies using isolated and frozen muscle.