Membrane excitability and celluar Ca2+ homeostasis in intact muscle cells from deep sea fish salvaged during an open sea expedition in 2007: elucidating mechanismus that correlate with adaption to ambient elevated pressure at depth
Zusammenfassung der Projektergebnisse
During a scientific cruise with the German research vessel ,Sonne' in the Pacific Ocean in July 2007, the project leader of the 'skeletal muscle biophysics' team was supported by the DFG to participate on this cruise and to conduct single cell functional experiments on skeletal muscle tissue from deep sea fish. Skeletal muscle is the source of locomotion in all animals and it is usually thought that the mechanisms underlying force production and movement are well understood. Although this might hold true for most of the terrestrial species this might not necessarily be transferable to deep sea animals that must withstand very high hydrostatic pressures during their life time. Also, these pressure loads may vary substantially in animals actively performing vertical migrations, e.g. diurnal migrations, prey migrations or mating migrations. High hydrostatic pressures have been found to markedly impair muscle function in mammalian muscles, i.e. slowing down reaction kinetics and movement. As compensatory mechanisms that might have evolved in deep sea fish to withstand pressure are difficult to assess in animals that have been commercially trawled and probably arrive on land hours later, the present project aimed to investigate muscle membrane excitability and Ca2+ regulation in single skeletal muscle cells from freshly trawled deep sea fish during this scientific cruise. Single cells were obtained from different species and different depths during the three week cruise duration. The researchers brought sophisticated fluorescence microscopy and electrophysiology rigs from Germany to be set up in the laboratories of the vessel. It was planned to record action potentials from single muscle cells and simultaneously record Ca2+ transients that reflect action potential induced Ca2+ release from internal stores. The kinetics of both surface membrane ion channel and intracellular Ca2+ release and depositing was thought to provide information about how these cells might be adapted to the overall decelerating effect prolonged high pressure exposure persistently has in mammals. The project had to face several complications. First of all, the sampling outcome can be considered poor as in 25 % of the trawls either the nets were empty or only small and already unpredictably long dead fish were recovered. In the remaining trawls, muscle tissue was dissected but was found to react very differently to the enzymatic isolation procedure so that no standard could be given. Sometimes cells were not isolated at all or, in contrast, all cellular material was digested on the same incubation time. In the few experiments that could be started on single cells, mechanical high frequency vibration from the running engine and low frequency vibration from the wave movements almost always prevented stable penetration with intracellular microelectrodes. In two experiments, stable resting membrane potentials could be recorded from single cells but, however, were so depolarised that action potentials could not be elicited. It was also attempted to repolarise cells but the membrane resistance was found to be three orders of magnitude smaller than usually found in intact mammalian fibres. In summary, the initial goals could not be fulfilled. However, conditions were identified that have to be improved in future attempts to perform 'on site' single cell physiology experiments. It is crucial to have an adequate anti-vibration system on board, e.g. an actively dampening table, to overcome mechanical vibrations. Also, the sample outcome could be improved. In this cruise, it turned out to be already very late in the year with winter weather conditions approaching the Southern hemisphere, i.e. strong winds and waves. During this time of the year, deep sea fish are known to remain...deep.
