Involvement of integrins in mechanical stress-induced local Ca<SUP>2+</SUP> influx, Ca<SUP>2+</SUP> spots, in the presence of lysophosphatidic acid in cultured lens epithelial cells

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The mechanisms of mechanical stress-induced local Ca2+ influx through mechanosensitive (MS) channels, e.g., Ca2+ spots, which are enhanced by lysophosphatidic acid (LPA), were examined by real-time confocal microscopy in cultured bovine lens epithelial cells loaded with a fluorescent Ca2+ indicator, fluo-4. The starting region of Ca2+ spots was located predominantly on the end of actin filaments stained with phalloidin-oregon green 488. Pretreatment with C3 ADP ribosyl-transferase, which inactivates rho protein, inhibited the formation of actin stress fibers; however, the density of LPA-induced Ca2+ spots was unaffected. Neither an inhibitor of rho-associated protein kinase (Y-27632), nor an inhibitor of actin polymerization (cytochalasin D), affected the density of LPA-induced Ca2+ spots, suggesting that rho-related cytoskeletal changes are not involved in the generation of LPA-induced Ca2+ spots. The pretreatment of extracellular matrix proteins with an inhibitor of integrin binding (GRGDNP) significantly inhibited LPA-induced Ca2+ spots. In contrast, similar treatment with an inactive control peptide (GRGESP) did not. Immunoreactivity with anti-integrin β1 chain antibody was observed at the starting regions of Ca2+ spots. These findings demonstrate the involvement of the mechanotransducer function of integrins, but not the formation of actin stress fibers, in LPA-induced Ca2+ spots, which are a result of mechanical stress-induced local [Ca2+]i influx. LPA may sensitize MS channels via activation of this integrin function. In addition, these results strongly suggest that LPA functions as an endogenous mechanosensitizer, which enhances the mechanical stress-induced pathogenesis, including cataract formation.

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  • bioimages

    bioimages 16 (0), 19-29, 2008

    Bioimaging Society

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