September 1993
Volume 34, Issue 10
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Articles  |   September 1993
Calcium regulation in tissue-cultured human and bovine lens epithelial cells.
Author Affiliations
  • G Duncan
    School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
  • S F Webb
    School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
  • A P Dawson
    School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
  • M D Bootman
    School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
  • A J Elliott
    School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
Investigative Ophthalmology & Visual Science September 1993, Vol.34, 2835-2842. doi:
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    • Get Citation

      G Duncan, S F Webb, A P Dawson, M D Bootman, A J Elliott; Calcium regulation in tissue-cultured human and bovine lens epithelial cells.. Invest. Ophthalmol. Vis. Sci. 1993;34(10):2835-2842.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

PURPOSE: To study calcium regulatory mechanisms in lens cells with particular reference to the relative contributions from the calcium adenosine triphosphatase of plasma and endoplasmic reticulum membranes, respectively. METHODS: The calcium-sensitive fluorescent dye, Fura 2, was incorporated into tissue-cultured human and bovine epithelial cells and internal calcium was calibrated using the ionomycin (1 microM) method. The dynamics of calcium release from the endoplasmic reticulum were also studied in digitonin-permeabilized bovine cells. RESULTS: Tissue-cultured bovine and human lens cells have very similar resting calcium levels (235 +/- 22 nM and 216 +/- 12 nM, respectively). Thapsigargin caused an increase in cytoplasmic calcium both in the presence and absence of external calcium, but the calmodulin antagonist W7 only initiated an increase in the presence of external Ca2+. The effects of thapsigargin and W7 were additive. Exposing lens cells to Na(+)-free perfusing solutions caused a transient increase in internal Ca2+. Bovine lens cells permeabilized by digitonin-released Ca2+ when exposed to inositol (1,4,5) triphosphate and the effect was maximal at 1 microM. CONCLUSIONS: Lens cytoplasmic calcium is controlled by calcium adenosine triphosphatases at the plasma and endoplasmic reticulum membranes. The former is inhibited by W7 and insensitive to thapsigargin whereas the latter is inhibited by thapsigargin, but insensitive to W7. The lens endoplasmic reticulum store is also controlled by an inositol (1,4,5) trisphosphate calcium-release mechanism. Na+/Ca2+ exchange plays a relatively minor role in calcium regulation, at least at resting calcium levels.

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