Calcium ATPase activity and membrane structure in clear and cataractous human lenses.
OBJECTIVE
Maintenance of calcium homeostasis is imperative for the clarity of the lens. Ca(2+)-ATPase is essential for the removal of cytosolic calcium, either across the plasma membrane or through intracellular organelles such as the endoplasmic reticulum. In this study, membranes prepared from clear lens epithelium were compared to membranes prepared from cataractous lens epithelium.


METHODS
Human lens membranes were prepared by a protocol utilizing homogenization and centrifugation. Ca(2+)-ATPase activity was measured biochemically using Gamma-32P labeled ATP. Lipid order was measured using infrared and Raman spectroscopy.


RESULTS
Ca(2+)-ATPase activity was similar in membranes prepared from cataractous lenses that were classified as nuclear subcapsular, nuclear and brunescent cataracts. Ca(2+)-ATPase activity was approximately 50% less in membranes prepared from cataractous lenses in comparison to clear lenses. Because clear lenses from Indian donors was unavailable, clear human lenses were used as a qualitative control for the measurement for Ca(2+)-ATPase activity. Lipid order was measured in lens fibers from cataractous and clear lenses from the United States donors. Lipid order increased from 55% in the hydrocarbon chains from clear lens fibers to 84% in cataractous lens fibers.


CONCLUSIONS
These findings support the hypothesis that membranes are deranged in cataractous tissue, which should lead to altered levels of calcium.
Paterson
C A
CA
Department of Ophthalmology and Visual Sciences, Kentucky Lions Eye Research Institute, University of Louisville School of Medicine 40202, USA.
Zeng
J
J
Husseini
Z
Z
Borchman
D
D
Delamere
N A
NA
Garland
D
D
Jimenez-Asensio
J
J
D000328:Adult; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism*; D002386:Cataract / Q000378:metabolism*; D005260:Female; D006801:Humans; D007908:Lens, Crystalline / Q000378:metabolism*; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008297:Male; D008566:Membranes / Q000378:metabolism; D008875:Middle Aged; D012016:Reference Values; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman
D008055:Lipids; D000252:Calcium-Transporting ATPases