Membrane lipid biosynthesis in the Philly mouse lens. I. The major phospholipid classes

The presence of toluidine blue-staining vesicles and leaky membranes in the Philly mouse lens as early as 10 days after birth led us to investigate the phospholipid metabolism of these lenses. On a dry weight, or per lens, basis, the Philly mouse lens had a slightly higher than normal concentration of phosphatidyl choline (PC), phosphatidyl ethanolamine (PE), sphingomyelin (S) and cholesterol (C) at 10 days. The levels of PC and PE dropped between 10 and 30 days in the Philly mouse, while in the control lenses the amounts of both phospholipids, on a per lens basis, was increasing. 32P incorporation indicated an increased rate of turnover in the Philly lenses. Cholesterol and sphingomyelin concentrations closely paralleled the dry weight per lens curves in the Philly and control, Swiss-Webster, lenses. Sphingomyelin specific activity dropped rapidly in the first 10 day period, possibly reflecting the lowered PC pool available for S biosynthesis. These results suggest a lower utilization of biosynthesized lipids for membrane assembly in the Philly lens. The observed higher turnover of metabolically-active phospholipid supports the presence of increased degradative activity which may, in turn, result in leaky membranes and, thus, contribute to cataract development.