The lipid composition of hypodermal membranes from the blue crab (Callinectes sapidus) changes during the molt cycle and alters hypodermal calcium permeability

Crustaceans are covered by a cuticle that does not grow. In order for an individual to grow, the cuticle must periodically be shed (ecdysis). Replacement of the old cuticle with a new one depends on processes that require precise timing and control, yet the nature and location of these controls remain unclear. A candidate site for them is within the hypodermal microvilli. These cellular structures extend through pore canals deep into the acellular cuticular matrix. Changes in the lipid composition of hypodermal microvilli could modulate water and ion fluxes and enzyme activities during critical stages of the molt cycle; however, the lipid composition of these structures has not been assessed during the molt cycle. Data presented here show that phospholipids isolated from hypodermal microvilli of Callinectes sapidus initially have elevated levels of n-6 fatty acids that decline steadily beginning just after ecdysis. Experiments with liposomes reveal that n-6 fatty acids decrease the calcium permeability of membranes, suggesting that the initially elevated levels in the cuticle may function to reduce calcium flux from the cuticle into the hypodermis. In addition, the ratio of cholesterol to phospholipid and the proportion of oleic acid in membrane phospholipids are maximal at 6 h post-ecdysis. It is known that changes in cholesterol and oleic acid content alter membrane permeability to water. It is, therefore possible that water flux through hypodermal membranes is also modulated in the early post-molt cuticle. Changes in microvillar lipid composition might serve importantly to control biomineralization in the post-ecdysal cuticle.