Distribution of membrane phospholipids in the crystalline lens

To determine the phospholipid content of specific anatomic regions within the crystalline lens.

Phospholipid extracts of tissues dissected from 5 sets of 10 rabbit lenses were analyzed by 31P nuclear magnetic resonance spectroscopy. Twenty-nine pathway-specific metabolic indexes were calculated from groups of phospholipids and ratios of phospholipids.

Phospholipid levels (mole percent) were determined from the capsule with attached epithelium, the cortex, and the nucleus. Eleven phospholipids were detected with significant regional differences in the lens phospholipid profiles. The levels of phosphatidylcholine (PC), PC plasmalogen-alkylacyl PC, phosphatidylinositol (PI), phosphatidylethanolamine (PE), and diphosphatidylglycerol (DPG), and of the lyso derivatives (lyso PC and lyso PE) were greater in the capsule plus epithelium than in the cortex or the nucleus. Levels of sphingomyelin, phosphatidylserine, and PE plasmalogen (EPLAS) were less in the capsule plus epithelium than in the cortex or the nucleus. PC, PC plasmalogen-alkylacyl PC, EPLAS, and lyso PE had nearly equal amounts in the cortex and the nucleus. PI, lyso PC, and DPG could not be detected in the nucleus. DPG was only detected in the capsule plus epithelium. An unidentified phospholipid at 0.13 ppm was approximately equal in the cortex and the nucleus, but it could not be detected in the capsule plus epithelium.

These differences demonstrate a significant heterogeneity among these anatomic regions of the lens, and differences in the nucleus relative to other regions studied are consistent with those in membranes that less readily undergo transitions from the relatively impermeable lamellar phase to the more permeable hexagonal HII phase.