Effects of Heatshock on the Na+/K+-ATPase in Locusta migratoria
Hou, Nicholas Yue
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Most vertebrates suffer permanent damage after minutes of anoxia. Many insects however, have part of their life cycle in anoxia or constant hypoxia, such as during their egg-hatching phase, by living as deep burrowers, or at high altitudes. Insects are able to survive in anoxia from hours to days, or even months by developing various strategies through evolution. For example, the locusts (Locusta migratoria) enter a reversible coma during anoxia that is associated with an arrest of ventilation, and a reinitiation of ventilation when returned to normoxia. This coma is correlated with a surge in the concentration of extracellular potassium ions ([K+]o), and recovery from this reversible coma is dependent on re-establishing the functional [K+]o. Prior exposure to a sublethal heatshock (HS)-preconditioning grants locusts a temporary resilience to anoxia; however, the molecular mechanisms of this protection are still unclear. This project investigated the effects of HS-preconditioning on locusts’ ventilation, the total enzymatic activity of the Na+/K+-ATPase, as well as its distribution within the metathoracic ganglion and tested the hypothesis that HS-preconditioning alters locusts’ ventilation and increases the totally Na+/K+-ATPase activity and its concentration within neuronal membranes. I recorded electromyograms of locusts’ ventilatory motor patterns in the presence and absence of anoxic coma by placing a copper wire electrode on ventilatory muscles 161 or 173 in control and HS-preconditioned animals. In addition, I studied the enzymatic activity of the Na+/K+-ATPase using a pyruvate kinase/lactate dehydrogenase assay and the localization of the Na+/K+-ATPase using immunohistochemistry in control and HS-preconditioned locusts at different stages of coma. I found that the ventilatory cycle period was decreased and the ventilatory muscle burst duration was increased after recovery from anoxic coma in HS-preconditioned locusts. I also found that anoxia did not affect the activity or the localization of the Na+/K+-ATPase. However, HS-preconditioning increased the total activity of the Na+/K+-ATPase and the localization of the Na+/K+-ATPase within the neuronal membranes. From this project, I concluded that HSpreconditioning affected locusts’ ventilatory motor pattern after recover from anoxia and increased the total activity and the neuronal membrane localization of the Na+/K+-ATPase.