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Journal of Cell Science, Vol 109, Issue 2 355-365, Copyright © 1996 by Company of Biologists
JOURNAL ARTICLES |
GC Churchill, MM Atkinson and CF Louis
Department of Biochemistry, University of Minnesota, St Paul 55108, USA.
Although abnormalities in calcium regulation have been implicated in the development of most forms of cataract, the mechanisms by which Ca2+ is regulated in the cells of the ocular lens remain poorly defined. Cell-to-cell Ca2+ signaling was investigated in primary cultures of ovine epithelial cells using the Ca(2+)-reporter dye fura-2 and fluorescence microscopy. Mechanical stimulation of a single cell with a micropipette initiated a propagated increase in cytosolic free Ca2+ that spread from the stimulated cell through 2-8 tiers of surrounding cells. During this intercellular Ca2+ wave, cytosolic Ca2+ increased 2- to 12-fold from resting levels of approximately 100 nM. Nanomolar extracellular Ca2+ did not affect the cell-to-cell propagation of the Ca2+ wave, but reduced the magnitude of the cytosolic Ca2+ increases, which was most evident in the mechanically-stimulated cell. Depletion of intracellular Ca2+ stores with thapsigargin eliminated the propagated intercellular Ca2+ wave, but did not prevent the cytosolic Ca2+ increase in the mechanically-stimulated cell, which required extracellular Ca2+ and was attenuated by the addition of the Ca2+ channel blockers Ni2+, Gd3+ and La3+ to the medium. These results are most easily explained by a mechanically-activated channel in the plasma membrane of the stimulated cell. The propagated increase in cytosolic Ca2+ appeared to be communicated to adjacent cells by the passage of an intracellular messenger other than Ca2+ through gap junction channels. However, if the plasma membrane of the mechanically-stimulated cell was ruptured such that there was loss of cytosolic contents, the increase in cytosolic Ca2+ in the surrounding cells was elicited by both a messenger passing through gap junction channels and by a cytosolic factor(s) diffusing through the extracellular medium. These results demonstrate the existence of intercellular Ca2+ signaling in lens cells, which may play a role in regulating cytosolic Ca2+ in the intact lens.
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