The pulmonate snail, <i>Helix aspersa</i>, has the ability to survive long bouts of anoxia by depressing its metabolism. Direct calorimetry was used to measure the metabolic heat production of the snails in this state. During 24-48 hrs of anoxia, heat production varied with the oxygen levels and fell as low as 2% of that during normoxia. The <i>Helix </i>central nervosa system also depressed its metabolism during anoxia. Electrophysiological recordings revealed decreases in both action potential firing (spike arrest) and membrane conductance (channel arrest). These processes allow the maintenance of ionic gradients during a period when ion pumping has presumably been down-regulated to conserve ATP. These abilities to respond to anoxia were found in both whole brains and isolated neurons. The mitochondrial inhibitor antimycin resulted in responses very similar to those seen in anoxia. This may be due to the fact that mitochondrial blockade with antimycin results in an increased production of reactive oxygen species, intracellular messengers which have been implicated in the anoxia responses of several cell types. The similar responses of anoxia and antimycin suggest that a high concentration of oxygen radicals triggers entry into metabolic depression. Support for this hypothesis came from neurons incubated in ascorbate (an antioxidant). With the amount of reactive oxygen species diminished, these neurons no longer responded to an anoxic challenge, evidence for the importance of reactive oxygen species in the anoxia response of snails. During anoxia, intracellular calcium levels are protected by an upregulated Ca<sup>2+</sup> pump, resulting in the rapid clearance of any calcium transients and a decreased basal calcium level. These experiments have revealed the potential for the snail to become a model organism in the study of oxygen sensing and metabolic depression.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:596873 |
| Date | January 2007 |
| Creators | Braun, Marvin Herbert |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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