Author(s): Rhodes JD, Russell SL, Illingworth CD, Duncan G, Wormstone IM
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Abstract PURPOSE: An elevated level of Ca(2+) is an important factor in cataract, yet precisely how Ca(2+) enters the lens is unknown. Lens epithelial cells contain a range of G-protein-coupled receptors and receptor tyrosine kinases that induce increases in intracellular Ca(2+). Receptor-associated Ca(2+) influx is, therefore, likely to be an important route for Ca(2+) influx to the lens. The authors investigated stimulated and passive Ca(2+) influx in in situ human lens epithelium. METHODS: Ca(2+) changes in equatorial (E) and central anterior (CA) epithelial cells were monitored with the use of a Ca(2+) indicator (Fluo4) and confocal microscopy. Gene expression was monitored by RT-PCR and immunoblotting. RESULTS: Adenosine triphosphate (ATP) induced Ca(2+) responses that were smaller in CA than E. Ca(2+) store depletion, using ATP (100 microM) or thapsigargin (1 microM), revealed greater relative store capacity and Ca(2+) influx in E. Ca(2+) influx was blocked by La(3+) (0.5 microM) in both regions. Unstimulated Ca(2+) influx was greater in E than CA. Greater expression of Orai1 and STIM1 was detected in E than in CA. CONCLUSIONS: Greater Ca(2+) store capacity and Ca(2+) influx in E compared with CA reflects underlying differences in proliferation and differentiation between the regions. The relatively small resting Ca(2+) influx in CA epithelium suggests that store-operated Ca(2+) entry (SOCE) is the main route of Ca(2+) influx in these cells. Greater resting influx and SOCE in E cells suggests that these are a major route for Ca(2+) influx into the lens. Increased expression of Orai1 and STIM1 in E could account for the differences in Ca(2+) entry. Receptor activation will modulate Ca(2+) influx, and inappropriate activity may contribute to cortical cataract.
This article was published in Invest Ophthalmol Vis Sci
and referenced in Journal of Clinical & Experimental Ophthalmology