Biomedical subjects

M Langenbuch

Publications and source records attributed to M Langenbuch.

6 recordsLinked to original sources

PubMed2006

Effects of environmental hypercapnia on animal physiology: a 13C NMR study of protein synthesis rates in the marine invertebrate Sipunculus nudus.

Global climate change is associated with a progressive rise in ocean CO(2) concentrations (hypercapnia) and, consequently, a drop in seawater pH. However, a comprehensive picture of the physiological mechanisms affected by chronic CO(2) stress in marine biota is still lacking. Here we present an analysis of protein biosynthesis rates in isolated muscle of the marine invertebrate Sipunculus nudus, a sediment dwelling worm living at various water depths. We followed the incorporation of (13)C-labelled phenylalanine into muscular protein via high-resolution NMR spectroscopy. Protein synthesis decreased by about 60% at a medium pH of 6.70 and a consequently lowered intracellular pH (pHi). The decrease in protein synthesis rates is much stronger than the concomitant suppression of protein degradation (60% versus 10-15%) possibly posing a threat to the cellular homeostasis of structural as well as functional proteins. Considering the progressive rise in ocean CO(2) concentrations, permanent disturbances of cellular protein turnover might seriously affect growth and reproductive performance in many marine organisms with as yet unexplored impacts on species density and composition in marine ecosystems.

Animals↗

PubMed2004

High sensitivity to chronically elevated CO2 levels in a eurybathic marine sipunculid.

CO2 levels are expected to rise (a) in surface waters of the oceans as atmospheric accumulation continues or (b) in the deep sea, once industrial CO2 dumping is implemented. These scenarios suggest that CO2 will become a general stress factor in aquatic environments. The mechanisms of sensitivity to CO2 as well as adaptation capacity of marine animals are insufficiently understood. Here, we present data obtained in Sipunculus nudus, a sediment-dwelling marine worm that is able to undergo drastic metabolic depression to survive regular exposure to elevated CO2 levels within its natural habitat. We investigated animal survival and the proximate biochemical body composition during long-term CO2 exposure. Results indicate an unexpected and pronounced sensitivity characterized by the delayed onset of enhanced mortality at CO2 levels within the natural range of concentrations. Therefore, the present study contrasts the previously assumed high-CO2 tolerance of animals adapted to temporary hypercapnia. As a consequence, we expect future loss of species and, thereby, detrimental effects on marine benthic ecosystems with as yet poorly defined critical thresholds of long-term tolerance to CO2.

Adaptation, Physiological↗

PubMed2003

Energy budget of hepatocytes from Antarctic fish (Pachycara brachycephalum and Lepidonotothen kempi) as a function of ambient CO2: pH-dependent limitations of cellular protein biosynthesis?

Scenarios of rising CO2 concentration in surface waters due to atmospheric accumulation of anthropogenic CO2, or in the deep sea due to anticipated industrial dumping of CO2, suggest that hypercapnia (elevated partial pressure of CO2) will become a general stress factor in aquatic environments, with largely unknown effects on species survival and well being, especially in cold and deep waters. For an analysis of CO2 effects at the cellular level, isolated hepatocytes were prepared from two representatives of the Antarctic fish fauna, Pachycara brachycephalum and Lepidonotothen kempi. Correlated changes in energy and protein metabolism were investigated by determining the rates of oxygen consumption at various levels of PCO2, of intra- and extracellular pH, and after inhibition of protein synthesis by cycloheximide. A decrease in extracellular pH (pHe) from control levels (pHe 7.90) to pHe 6.50 caused a reduction in aerobic metabolic rate of 34-37% under both normocapnic and hypercapnic conditions. Concomitantly, protein biosynthesis was inhibited by about 80% under conditions of severe acidosis in hepatocytes from both species. A parallel drop in intracellular pH probably mediates this effect. In conclusion, the present data indicate that elevated PCO2 may limit the functional integrity of the liver due to a pronounced depression in protein anabolism. This process may contribute to the limits of whole-animal tolerance to raised CO2 levels.

Analysis of Variance↗

PubMed2002

Changes in metabolic rate and N excretion in the marine invertebrate Sipunculus nudus under conditions of environmental hypercapnia: identifying effective acid-base variables.

Increased CO(2) partial pressures (hypercapnia) as well as hypoxia are natural features of marine environments like the intertidal zone. Nevertheless little is known about the specific effects of CO(2) on metabolism, except for the well-described effects on acid-base variables and regulation. Accordingly, the sediment-dwelling worm Sipunculus nudus was used as an experimental model to investigate the correlation of acid-base-induced metabolic depression and protein/amino acid catabolism, by determining the rates of oxygen consumption, ammonia excretion and O/N ratios in non-perfused preparations of body wall musculature at various levels of extra- and intracellular pH, P(CO(2)) and [HCO(3)(-)]. A decrease in extracellular pH from control level (7.9) to 6.7 caused a reduction in aerobic metabolic rate of both normocapnic and hypercapnic tissues by 40-45 %. O/N ratios of 4.0-4.5 under control conditions indicate that amino acid catabolism meets the largest fraction of aerobic energy demand. A significant 10-15 % drop in ammonia excretion, a simultaneous reduction of O/N ratios and a transient accumulation of intracellular bicarbonate during transition to extreme acidosis suggest a reduction in net amino acid catabolism and a shift in the selection of amino acids used, favouring monoamino dicarboxylic acids and their amines (asparagine, glutamine, aspartic and glutamic acids). A drop in intracellular pH was identified as mediating this effect. In conclusion, the present data provide evidence for a regulatory role of intracellular pH in the selection of amino acids used by catabolism.

Acid-Base Equilibrium↗

PubMed2001

The pancreas-specific protein disulphide-isomerase PDIp interacts with a hydroxyaryl group in ligands.

Using a cross-linking approach, we have recently demonstrated that radiolabelled model peptides or misfolded proteins specifically interact in vitro with two members of the protein disulphide- isomerase family, namely PDI and PDIp, in a crude extract from sheep pancreas microsomes. In addition, we have shown that tyrosine and tryptophan residues within a peptide are the recognition motifs for the binding to PDIp. Here we examine non-peptide ligands and present evidence that a hydroxyaryl group is a structural motif for the binding to PDIp; simple constructs containing this group and certain xenobiotics and phytoestrogens, which contain an unmodified hydroxyaryl group, can all efficiently inhibit peptide binding to PDIp. To our knowledge this is the first time that the recognition motif of a molecular chaperone or folding catalyst has been specified as a simple chemical structure.

Animals↗

PubMed2001

Alexithymia in male infertility.

The continuing confrontation with the thoughts and feelings surrounding an unfulfilled wish for a child makes coping very difficult. There is empirical evidence that, in medical illnesses associated with stress and loss of quality of life, patients react with alexithymia, which means a difficulty to communicate emotions. In this study we compared 84 infertile men with a group of 96 healthy men and 43 male psychosomatic outpatients concerning their ability to communicate feelings, measured by the Twenty-Item Toronto Alexithymia Scale and the amount of psychopathologically relevant symptoms, especially somatization, measured by the Symptom Checklist 90-R and a List of Complaints (Beschwerden-Liste). The results showed a significantly higher alexithymia in infertile men compared with healthy men (P < 0.05), but a significantly lower alexithymia compared with psychosomatic outpatients (P < 0.05). Furthermore the study group showed significantly more somatic complaints in the List of Complaints compared with healthy men (P < 0.05). The importance of alexithymia in male infertility is discussed on the basis of empirical results that it might play a defensive role as far as depression is concerned but on the other hand increases the possibility of somatic complaints. The need for prospective studies in further research is emphasized.

Adult↗