Purchase this article with an account.
J. D. Rhodes, S. L. Russell, C. D. Illingworth, I. M. Wormstone; Mechanisms of Calcium Entry in the Intact Human Lens. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4371.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Calcium (Ca2+) has been shown to have an important role in cataract. How Ca2+ enters the lens, however, is less well understood. We have, therefore, investigated Ca2+ influx in the intact human lens.
Ca2+ changes in equatorial (E) and central anterior (CA) epithelial cells of freshly isolated intact human lenses were monitored using a Ca2+-indicator (Fluo4) and confocal microscopy. Gene expression and protein levels were investigated by QRT PCR and Western blotting.
Un-stimulated Ca2+-influx was greater in E than CA cells. ATP (10 µM) induced Ca2+ responses were smaller in CA compared to E cells, indicating differences in store capacity and/or Ca2+-influx. Ca2+ store depletion by application of either ATP (100µM) or thapsigargin (TG; 1µM) in Ca2+-free conditions, revealed greater relative store capacity and Ca2+-influx in E than CA cells. However, major differences in the characteristics of Ca2+-influx were found between the 2 regions, that were dependent on the method used to deplete the Ca2+-stores. Ca2+-influx, induced following store depletion by ATP, was blocked by La3+ (0.5 µM) applied acutely to the Ca2+-influx, in both regions and was inhibited by 2APB (50 µM) only in E cells. Ca2+-influx in E cells, induced following store depletion by TG, however, was insensitive to La3+ (10uM) applied acutely to the Ca2+-influx and was stimulated by 2APB. In CA cells Ca2+-influx induced by TG was blocked by La3+ (0.5 µM) and was insensitive to 2APB. Interestingly, adding La3+ (0.5 µM) before Ca2+ was readmitted to the perusate greatly potentiated Ca2+-influx, induced by TG, in E but not in CA cells. RNA and protein for Orai1 and STIM1 were detected in CA and E epithelial samples. Expression of TRPC3 was restricted to E cells while there was greater expression of TRPC1 in CA cells.
Greater Ca2+ store capacity and Ca2+-influx in E compared to CA cells reflect underlying differences in proliferation and differentiation between the regions. Relatively small resting Ca2+-influx in CA epithelium suggests that store operated Ca2+-entry (SOCE) is the main route of Ca2+-influx in these cells. Major differences in the characteristics of Ca2+-influx between the regions of the epithelium indicate a complicated interplay between SOCE and TRPC channels. In vivo, receptor activation will modulate Ca2+-influx into the lens and inappropriate activity may be a contributory factor in cortical cataract.
This PDF is available to Subscribers Only