Aerobic and anaerobic energy metabolism in the brown shrimp (Crangon crangon) during moderate hypoxia.
In the marine environment low oxygen levels (hypoxia) and even complete oxygen depletion (anoxia) are not uncommon phenomena. Many marine animals are oxyregulators, which means that they are able to maintain constant oxygen consumption in spite of decreasing oxygen levels in the surrounding water. However, below a certain oxygen level they cant keep the oxygen consumption constant and they switch to oxyconformity, which means that the rate of oxygen consumption becomes proportional to the oxygen level of the surrounding water. The oxygen level at which an oxyregulator shifts to oxyconformity is called the critical oxygen tension (Pcrit). Below the Pcrit the oxygen consumption decreases proportional to the decrease in oxygen tension in the surrounding water. The consumed oxygen is a proxy for the energy produced in the cellular respiration, in which the overall reaction of complete oxidation of glucose: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O yields 36 ATP (i.e., 1 O2 consumed is equivalent to an energy output of 6 ATP). When oxygen consumption is decreasing the available energy is also decreasing, which forces the animal to be less active. In the range from the Pcrit and down to the arrest of aerobic respiration an animal might be partially anaerobic. Thus, the animal might produce some additional energy based on anaerobic metabolism: C6H12O6 + 2 ADP + 2 Pi → 2 lactate + 2 ATP (i.e., 1 lactate produced is equivalent to an energy output of 1 ATP). The lactate produced, will if the animal is returned to well oxygenated water, be re-oxidized back to glucose. This process can be seen as a time period with elevated oxygen consumption as compared to the normal oxygen consumption and is called oxygen debt. The re-oxidation of 1 lactate costs 6 ATP and because 1 O2 consumed produces 6 ATP the surplus of oxygen can be taken as a direct proxy for the amount of lactate produced. Finally, because 1 lactate produced is equivalent to an energy output of 1 ATP, the energy output from anaerobic metabolism can be estimated. Thus, the total energy output together with the reduction in available energy at decreasing oxygen tension can be estimated.
The aim of the project is to study the decrease in total available energy at oxygen tensions below the Pcrit in the brown shrimp (Crangon crangon, Danish: hestereje) and/or the Baltic prawn (Palaemon adspersus, Danish: Fjordreje eller Roskildereje) and/or the rockpool shrimp (Palaemon elegans, Danish: Tangreje).
|Anvendte metoder:||Intermittent respirometry|
|Keywords:||Hypoxia, oxygen consumption, oxygen debt, energy output estimation, marine invertebrates|