Anaerobic metabolism and thermal tolerance: The importance of opine pathways on survival of a gastropod after cardiac dysfunction.

Organisms on rocky shores are frequently exposed to high temperatures, which cause impairment of cardiac function and retard cellular oxygen delivery. However, some gastropods can survive at several degrees Celsius higher than their Arrhenius break temperature of cardiac function (ABT), indicating the importance of anaerobic metabolism for their thermal tolerance. We measured the global molecular responses to heat stress in limpet Cellana toreuma using 454 GS-FLX to investigate the variations of genes involved in anaerobic metabolism at high temperatures. Next, the gene expression levels of 4 anaerobic enzymes and activity of alanopine dehydrogenase (AlDH), which is involved in opine pathway, were measured in response to elevated temperature. A total of 19 heat shock proteins (HSPs) were determined using real-time PCR at different temperatures. At high temperatures, the extensive upregulation of HSP genes was an effective but energetically expensive form of protection to prevent thermal damage. The upregulation of hypoxia-inducible factor 1 alpha mRNA indicated the condition of cellular hypoxia and the high gene expression and enzyme activity of AlDH suggested that opine pathway was the main anaerobic pathway. These results implied that anaerobic metabolism was enhanced to provide energy in the face of thermal stress. Our findings highlight the ecological significance of the anaerobic metabolism of gastropods to thermal adaptation. For predicting the ecological impact of global warming on the distribution of gastropods, the role of anaerobic pathways should be evaluated.