ANDERSON, M.J.; MILLER , J.T. ; DAHILL, D.; CRIMMINS, M.J. ; MATTHEWS, C.A. ; WILLIAMS, E.E. ; Salisbury University: Membrane lipid involvement in the molt cycle of the blue crab (Callinectes sapidus)

The lipids of cell membranes are intricately involved in regulating fluxes of both water and ions. We examined the lipid content of gill filaments and of the hypodermal microvilli of carapace during the first hours after ecdysis in the blue crab. At the time of ecdysis the lipid content of carapace was 6-fold higher than in intermolt crabs. Beginning 24 hours post-molt, the lipid content of the carapace declined rapidly, reaching pre-molt values by 72 hours. In gill, anterior filaments contained twice the lipid as posterior filaments during the same 24 hour post-molt interval, and did not change during that interval. The total lipid fraction extracted from these tissues was separated into neutral lipid and phospholipid fractions by silicic acid chromatography. Cholesterol content of the neutral lipid pool was assayed. The phospholipids were resolved into phosphatidylcholine (PC) and phosphatidylethanolamine (PE) pools by thing layer chromatography and the fatty acid composition of each pool was assessed by gas chromatography. Cholesterol content of the carapace rose from 20 ug/g tissue at ecdysis to 70 ug/g 6 hours later. In contrast, the cholesterol content of the anterior gill filaments was maximal at ecdysis (69 ug/g) and reached a minimum of 9 ug/g at 6 hours. The cholesterol content of the posterior gill remained low (near 5ug/g) during the 24 h post-molt period. In addition, the pool of fatty acids in the PC fraction of the anterior gill filaments was much more highly saturated than either the PE pool of the same filaments or the PC and PE pools of both the posterior filaments and the carapace. These changes in cholesterol and saturated fatty acid content are known to reduce membrane permeability to water, and may contribute importantly to molting.