Plasma membrane Ca-ATPase isoform expression in human cataractous lenses compared to age-matched clear lenses.

The plasma membrane calcium ATPase (PMCA) pump is the major mechanism by which calcium is removed from the lens. The aim of this study was to determine if mRNA and proteins levels of PMCA isoforms changed with age or lens opacity. mRNA was quantified using a quantitative real-time reverse transcription polymerase chain reaction assay (RT-PCR). PMCA protein levels were quantified using Western blot analysis. No PMCA mRNA or proteins were detected in human lens fiber cells. The mRNA and protein levels of PMCA1, 3 and 4 in the epithelium of cataractous lenses were similar to those of epithelium from age-matched clear lenses and were also the same in younger lenses. PMCA2 mRNA and protein levels were 1.6-2.5 times higher, respectively, in cataractous lenses compared to age-matched clear lenses. Elevated PMCA2 expression in cataractous lenses might be a compensatory mechanism to overcome higher intracellular calcium levels in cataract.