Regional differences in store-operated Ca2+ entry in the epithelium of the intact human lens.
OBJECTIVE
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.
Rhodes
Jeremy D
JD
School of Biological Sciences, University of East Anglia, Norwich, United Kingdom. j.rhodes@uea.ac.uk
Russell
Sarah L
SL
Illingworth
Christopher D
CD
Duncan
George
G
Wormstone
I Michael
IM
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000814:Aniline Compounds / Q000378:metabolism; D001693:Biological Transport, Active; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics; D002454:Cell Differentiation; D049109:Cell Proliferation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D007908:Lens, Crystalline / Q000187:drug effects / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D018613:Microscopy, Confocal; D009363:Neoplasm Proteins / Q000235:genetics; D000071740:ORAI1 Protein; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071737:Stromal Interaction Molecule 1; D019284:Thapsigargin / Q000494:pharmacology; D014966:Xanthenes / Q000378:metabolism
D000814:Aniline Compounds; D015220:Calcium Channels; D004791:Enzyme Inhibitors; C409648:Fluo 4; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D012333:RNA, Messenger; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; D014966:Xanthenes; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D002118:Calcium