Stress and adaptation to environmental conditions can lead to changes in cellular signalling and to shifts in the allocation of cellular energy resources to specific metabolic processes, finally even resulting in ultrastructural changes in cellular organisation. We therefore investigate signal transduction processes in isolated cells and primary cultures as well as the thermal sensitivity of cellular energy budgets. Techniques investigating mitochondrial energy coupling, membrane potentials and proton leakage rates are frequently applied to isolated mitochondria and cells of various marine and terrestrial vertebrates and invertebrates. Furthermore, our laboratories provide the infrastructure to monitor cellular energy status by Multi-Nuclei-NMR spectroscopy and to examine changes in cellular ultra-structure by confocal laser scanning microscopy and transmission electron microscopy (TEM).