Biomedical subjects
Publications and source records attributed to David J Baker.
Taiozyma onychis (syn. Wickerhamomyces onychis) is a rare opportunistic human fungal pathogen. Here, we report the draft genome sequence of T. onychis NCYC 4433, a fecal isolate from a 62-year-old female.
Yamadazyma mexicana is an ascomycetous yeast with industrial utility. Here, we report the near-chromosome resolution genome sequence of Yamadazyma mexicana NCYC 1483, the species type strain.
The purpose of the present experiments was to test the hypotheses that: (i) nitric oxide synthase (NOS) inhibition reduces the O2 cost of force development across a range of contractile demands; and (ii) this reduced O2 cost of force development would be reflected in a sparing of intramuscular higher energy phosphates. Rat distal hindlimb muscles were pump perfused in situ and electrically stimulated (200 ms trains with pulses at 100 Hz, each pulse 0.05 ms duration) for 1 min each at 15, 30 and 60 tetani min(-1) and for 2 min at 90 tetani min(-1) in three groups: 0.01 mM adenosine; 1 mM D-NAME and 0.01 mM adenosine (D-NAME); and 1 mM L-NAME and 0.01 mM adenosine (L-NAME). The gastrocnemius-plantaris-soleus muscle group was freeze clamped post-contractions for metabolite analyses. Force was 19% higher and oxygen uptake (VO2) was 20% lower with L-NAME versus adenosine, and there was a 35% reduction in VO2/time-integrated tension versus adenosine and 24% versus D-NAME that was independent of contraction frequency. L-NAME treatment produced a 33% sparing of muscle phosphocreatine (PCr), and intramuscular lactate was no different between groups. In contrast, D-NAME reduced force by 30%, VO2 by 29% and the O2 cost of force development by 15% compared with adenosine, but had no effect on the degree of intramuscular ATP and PCr depletion. These results show that NOS inhibition improved the metabolic efficiency of force development, either by improving the ATP yield for a given O2 consumption or by reducing the ATP cost of force development. In addition, these effects were independent of contraction frequency.
The purpose of this study was to determine the effect of long-term caloric restriction (CR) on the age-associated decline of skeletal muscle aerobic function. Skeletal muscle maximal aerobic performance (VO2max) was assessed in ad libitum (AL) and CR rats aged 8-10 months and 35 months using a pump-perfused hindlimb model to match oxygen delivery to muscle mass between groups. Whereas there was a 46% decline in muscle mass-specific VO2max between 8-10 mo (524+/-13 micromol x min(-1) x 100 g(-1); mean+/- SE) and 35 mo (281+/-54 micromol x min(-1) x 100 g(-1)) in AL rats, not only did CR rats begin at the same point in 8-10 mo old rats (490+/-42 micromol x min(-1) x 100 g(-1)), we found no decline in 35 mo old CR animals (484+/-49 micromol x min(-1) x 100 g(-1)). Interestingly, although most markers of oxidative capacity began at a lower point in young adult CR animals, CR rats exhibited a higher in situ activity of complex IV at VO2max. This activity allows the young adult CR animals to exhibit normal aerobic capacity despite the lower oxidative enzyme activities. In stark contrast to the 19-41% decline in activities of citrate synthase, complexes I-III, and complex IV in homogenates prepared from the plantaris muscle and mixed region of gastrocnemius muscle with aging in AL rats, no age-related decline was found in CR animals. Thus, our results showed that CR preserves aerobic function in aged skeletal muscles by facilitating a higher in situ function of complex IV and by preventing the age-related decline in mitochondrial oxidative capacity.
We tested the hypothesis that an acute decrease in muscle TCA cycle intermediates during contraction would compromise aerobic energy delivery. Male Wistar rats were anaesthetized and the gastrocnemius-plantaris-soleus (GPS) muscle complex from one leg was isolated and perfused with a red cell medium containing either saline (Con) or cycloserine (Cyclo; 0.05 mg g-1), an inhibitor of alanine aminotransferase (AAT). After 1 h of perfusion, the GPS muscle was either snap frozen (Con-Rest, n=11; Cyclo-Rest, n=9) or stimulated to contract for 10 min (1 Hz, 0.3 ms, 2 V) with blood flow fixed at 30 ml min-1 (100 g)-1 and then snap frozen (Con-Stim, n=10; Cyclo-Stim, n=10). Maximal AAT activity was>80% lower (P<0.001) in both Cyclo-treated groups (Rest: 0.61+/-0.02; Stim: 0.63+/-0.01 mmol (kg wet wt)-1 min-1; mean+/-s.e.m.) compared to Con (Rest: 3.56+/-0.16; Stim: 3.92+/-0.29). The sum of five measured TCAI (SigmaTCAI) was reduced by 23% in Cyclo-Rest versus Con-Rest but this was not different (P=0.08). However, after 10 min of contraction, the SigmaTCAI was 25% lower (P=0.006) in Cyclo-Stim compared to Con-Stim (1.88+/-0.15 versus 2.48+/-0.11 mmol (kg dry wt)-1). Despite the acute decrease in TCAI after Cyclo treatment, the contraction-induced changes in markers of non-oxidative energy provision (phosphocreatine, ATP and lactate) and the decline in tension after 10 min of stimulation were similar compared to Con. These data do not support the hypothesis that the total muscle concentration of TCAI is causally linked to the rate of mitochondrial respiration during contraction.
There is an increasing risk of mass exposure of civil populations after release of toxic agents. These include military chemical warfare agents or industrial compounds, some of which have been used as a chemical. The traditional military divisions among chemical agents, toxins, and biologic agents may be viewed as a continuous spectrum of hazards. Each of these has four specific qualities (toxicity, latency, persistency, and transmissibility), which determine management of casualties and the toxic release. Toxic hazards may be released accidentally or deliberately, producing potentially large numbers of casualties. Previous incidents have shown that many of these require extended hospital care. This article reviews aspects of the nature of the toxic agents, the pathophysiology they produce, and therapeutic measures. The central and peripheral nervous systems and the respiratory systems are particularly vulnerable and may lead to fatal results unless early action is taken. Specific antidotes and life support care is required at all levels of prehospital and hospital management. Critical care management is required for severe cases, and this must combine continuing antidote, ventilatory and supportive therapy.
The pump-perfused rat hindlimb model, in various forms, has been in use for several decades. There are many applications for this model, owing to the ability to control the content and rate of perfusion. In the context of exercise physiology this model has been put to particularly good use. In this report we summarize some of the central surgical differences between different versions of the pump-perfused rat hindlimb model, including the double hindlimb + trunk, double hindlimb alone, single hindlimb, and distal hindlimb-alone models. We also summarize specific elements of the perfusion medium and measurement of force used in our lab during assessment of muscle metabolic and contractile responses, and illustrate some of the differences from the in vivo condition that merit consideration. We then provide specific examples of how the single pump-perfused hindlimb and distal hindlimb-alone versions of this model have been used to study muscle function and energy metabolism. In this context we show how this model can be used to permit the experimenter to manipulate and control the rate of O(2)delivery and to add specific compounds that inhibit a particular aspect of muscle metabolism, such that in combination with measurements of the flux of specific substances across the muscle and/or fast-freezing of muscle after contractions, more can be understood about the metabolic state of the contracting muscles.
Inhibition of hepatic glycogen phosphorylase is a promising treatment strategy for attenuating hyperglycemia in type 2 diabetes. Crystallographic studies indicate, however, that selectivity between glycogen phosphorylase in skeletal muscle and liver is unlikely to be achieved. Furthermore, glycogen phosphorylase activity is critical for normal skeletal muscle function, and thus fatigue may represent a major development hurdle for this therapeutic strategy. We have carried out the first systematic evaluation of this important issue. The rat gastrocnemius-plantaris-soleus (GPS) muscle was isolated and perfused with a red cell suspension, containing 3 micromol/l glycogen phosphorylase inhibitor (GPi) or vehicle (control). After 60 min, the GPS muscle was snap-frozen (rest, n = 11 per group) or underwent 20 s of maximal contraction (n = 8, control; n = 9, GPi) or 10 min of submaximal contraction (n = 10 per group). GPi pretreatment reduced the activation of the glycogen phosphorylase a form by 16% at rest, 25% after 20 s, and 44% after 10 min of contraction compared with the corresponding control. AMP-mediated glycogen phosphorylase activation was impaired only at 10 min (by 21%). GPi transiently reduced muscle lactate production during contraction, but other than this, muscle energy metabolism and function remained unaffected at both contraction intensities. These data indicate that glycogen phosphorylase inhibition aimed at attenuating hyperglycaemia is unlikely to negatively impact muscle metabolic and functional capacity.
Although mitochondrial DNA damage accumulates in aging skeletal muscles, how this relates to the decline in muscle mass-specific skeletal muscle aerobic function is unknown. We used a pump-perfused rat hind-limb model to examine maximal aerobic performance (VO(2max)) in young adult (YA; 8-9-month-old), late middle aged (LMA; 28-30-month-old) and senescent (SEN; 36-month-old) Fischer 344 x Brown Norway F1-hybrid rats at matched rates of convective O(2) delivery (QO(2)). Despite similar muscle QO(2) during a 4-minute contraction bout, muscle mass-specific VO(2max) was reduced in LMA (15%) and SEN (52%) versus YA. In plantaris muscle homogenates, nested polymerase chain reaction revealed an increased frequency of mitochondrial DNA deletions in the older animals. A greater reduction in the flux through electron transport chain complexes I-III than citrate synthase activity in the older animals suggests mitochondrial dysfunction consequent to mitochondrial DNA damage with aging. These results support the hypothesis that a reduced oxidative capacity, due in part to age-related mitochondrial dysfunction, contributes to the decline in aerobic performance in aging skeletal muscles.
We used a pump-perfused rat hind-limb preparation to compare young adult (YA: 8-9- month-old), late middle-aged (LMA: 28-29-month-old), and senescent (SEN: 36-month-old) rats at similar rates of convective O(2) delivery during a 4-minute contraction bout. We hypothesized that not only would VO(2) and lactate production be reduced, but also that contractile economy would be altered with aging. Peak tension was lower in LMA (42%) and SEN (71%) versus YA. VO(2) and lactate efflux was progressively lower with increasing age. Estimated adenosine triphosphate per N of force was increased in LMA (35%) and reduced in SEN (31%) versus YA. Myosin heavy chain (MHC) analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed a lower MHC type IIb and higher MHC type IIa/IIx in SEN versus YA. Therefore, whereas contractile economy is impaired in LMA, it is improved in SEN, and this latter effect may be due in part to reduced type IIb MHC.
Chronic stimulation of beta2-receptors with beta2-agonists causes desensitisation, which in skeletal muscle is accompanied by myosin heavy chain (MHC) remodelling, similar to that observed in heart failure patients. However, the mechanisms for this skeletal muscle remodelling are not well established. G protein-coupled receptor kinases (GRKs) specifically phosphorylate and desensitise G protein-coupled receptors during periods of agonist activation. However, desensitisation associated with prolonged agonist activation alters beta-adrenergic signalling, and downstream affects gene expression. We hypothesised that skeletal muscle remodelling induced by beta2-agonist administration could be regulated by GRK expression. Therefore the aim of this study was firstly to characterise which, if any, of the six known isoforms of GRK were expressed in skeletal muscle and then secondly to determine whether remodelled skeletal muscle induced by chronic beta2-agonist administration was accompanied by altered expression of GRK isoforms. Male Wistar rats were administered a beta2-agonist daily for 8 weeks, and the expression of MHC and GRKs examined in gastrocnemius and soleus muscles. Treatment with beta2-agonist caused a change in MHC in soleus from types I to IIA, and in gastrocnemius from MHC types IIA/IIX to IIB. Western blotting revealed that GRK2 and GRK5 were expressed in skeletal muscle. Furthermore, despite changes in MHC and differential muscle-specific expression of GRK isoforms, there was no significant change in expression of GRK2 and GRK5 in soleus or gastrocnemius following beta2-agonist administration. In conclusion the level of GRK expression is unlikely to be responsible for MHC switching following chronic beta2-receptor stimulation.