Calcium permeability in large unilamellar vesicles prepared from bovine lens cortical lipids

The loss of calcium homeostasis in the lens is thought to play an important role in cataract formation. Although both lens Ca(2+)-ATPase and membrane lipid permeability are essential to calcium homeostasis, membrane permeability has been studied less extensively. In the present study, the calcium permeability of large unilamellar vesicles (LUVs) prepared from bovine lens cortical lipids has been characterized. When a calcium gradient had been established by the addition of CaCl2 to the external medium, calcium influx through the membrane was monitored by calcium concentration sensitive changes in Fura-2 fluorescence as a function of time. The calcium permeability coefficient, P, was 4.46 x 10(-13) cm s-1 at 37 degrees C. This value was about 4 fold higher than that for LUVs prepared from egg phosphatidylcholine and many times higher than that for LUVs prepared from sphingomyelin. These results provide a basis for future studies of factors that influence the permeability of lens cell membranes to calcium.