Eicosapentaenoic acid regulates scallop (Placopecten magellanicus) membrane fluidity in response to cold

The lipid core of a biological membrane requires a certain degree of structural rigidity, but it must also be sufficiently fluid to permit lateral movement of the constituent lipids and embedded proteins. Ectotherms can counteract the ordering effects of reduced temperature by changing the structure of their membranes, a process known as homeoviscous adaptation (1). Although the content of unsaturated fatty acids in the membranes of ectothermic animals is generally known to increase in response to cold (2), no clear and direct relationship between unsaturated fatty acids and membrane fluidity has been established in marine organisms. For example, phospholipid molecular species containing docosahexaenoic acid (22:6omega3) are believed to be important in controlling finfish membrane fluidity (3-6), but a direct correlation between 22:6w3 and membrane fluidity has not been found (4, 5, 7, 8). In contrast, we show here a simple but very strong relationship between fluidity and a single polyunsaturated fatty acid, eicosapentaenoic acid (20:5omega3), in gill membranes from a marine bivalve mollusc, the sea scallop Placopecten magellanicus.