Sensitizing effect of lysophosphatidic acid on Ca2+ response to hypotonic stress in cultured lens epithelial cells.

The effects of lysophosphatidic acid (LPA), a bioactive phospholipid, on the response of the cytosolic free Ca2+ concentration (Ca2+]i) to hypotonic stress were studied in cultured bovine lens epithelial cells, to test whether LPA affects cellular swelling-mediated increase in Ca2+]i, which may relate to formation of sugar cataracts. Exposure of the cells to a 30% hypotonic stress caused only a slight increase in Ca2+]i. Pretreatment with LPA (10 microM) significantly augmented the hypotonic stress-induced Ca2+]i response, whereas addition of LPA to the cells did not affect Ca2+]i. The hypotonic stress-induced increase in Ca2+]i in the presence of LPA was inhibited by Gd3+, a blocker of mechanosensitive cation channels, but not by nicardipine, a L-type Ca2+ channel blocker, or thapsigargin, an inhibitor of endoplasmic reticulum-ATPase pump. These results show that LPA sensitizes the response to hypotonic stress via increase in Ca2+ influx through Gd3+-sensitive stretch-activated ion channels, and not via Ca2+ release from intracellular stores. On the other hand, LPA did not affect the Ca2+]i response to ATP, a Ca2+ mobilizing agonist. Therefore, LPA sensitizes the hypotonic stress-induced Ca2+]i response in lens epithelial cells, suggesting that LPA potentiates the development of cataracts induced by cellular swelling such as sugar cataract.