590 Tiere (Zoologie)
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The Arctic is undergoing strong environmental changes, affecting species and
whole biological communities. To assess the impact on these communities,
including their composition and functions, we need more information on their
current distribution and biology. In the High-Arctic tundra, dung from animals,
such as muskoxen (Ovibos moschatus), is a relatively understudied microhabitat
that may be attractive for organisms like dung-feeding insects as well as gastrointestinal
parasites. Using a DNA barcoding approach, we examined muskox
droppings from two Greenlandic regions for dung-dwelling invertebrates. In
15% of all samples, we found the DNA of insect species in the orders Diptera
and Lepidoptera. The saprophagous Diptera colonized dung differently in west
versus north-east Greenland and summer versus winter. In addition, we found
muskox dung harbouring endoparasitic nematodes in samples from both
regions. However, we could not find traces of saprophagous arthropods, such as
collembolans and mites, from the soil sphere. Our pilot study sheds a first light on the invertebrates living in this neglected Arctic microhabitat.
Regulation of metabolism is complex and involves enzymes and membrane transporters, which form networks to support energy dynamics. Lactate, as a metabolic intermediate from glucose or glycogen breakdown, appears to play a major role as additional energetic substrate, which is shuttled between glycolytic and oxidative cells, both under hypoxic and normoxic conditions. Transport of lactate across the cell membrane is mediated by monocarboxylate transporters (MCTs) in cotransport with H+, which is a substrate, a signal and a modulator of metabolic processes. MCTs form a “transport metabolon” with carbonic anhydrases (CAs), which not only provide a rapid equilibrium between CO2, HCO3– and H+, but, in addition, enhances lactate transport, as found in Xenopus oocytes, employed as heterologous expression system, as well as in astrocytes and cancer cells. Functional interactions between different CA isoforms and MCTs have been found to be isoform-specific, independent of the enzyme’s catalytic activity, and they require physical interaction between the proteins. CAs mediate between different states of metabolic acidosis, induced by glycolysis and oxidative phosphorylation, and play a relay function in coupling pH regulation and metabolism. In the brain, metabolic processes in astrocytes appear to be linked to bicarbonate transport and to neuronal activity. Here, we focus on physiological processes of energy dynamics in astrocytes as well as on the transfer of energetic substrates to neurons.