6. From these results, we propose that the Ca 2+ spot is an elementary Ca 2+ -influx event through MS channels directly coupled with the first step in mechanoreception In addition, our results strongly suggest that LPA functions as an endogenous factor affecting mechanotransduction systems.

ABSTRACT-The mechanotransduction mechanism is believed to play an important role in maintenance of cellular homeostasis in a wide variety of cell types. In particular, the mechanotransduction system in vascular endothelial cells may be an essential mechanism for local hemodynamic control. Elevations in intracellular free Ca]i) are an important signal in the initial step of mechanotransduction and mechanosensitive (MS) cation channels are thought to be a putative pathway; however, the molecular mechanisms remain unclear. We found that lysophosphatidic acid (LPA), a bioactive phospholipid, sensitizes the response of [Ca 2+ ]i to mechanical stress in several cell types. Employing real-time confocal microscopy, local increases in [Ca 2+ ]i in several regions within the cell during application of mechanical stress were clearly visualized in bovine lens epithelial and endothelial cells in the presence of LPA. The phenomenon was termed "Ca 2+ spots". Pharmacological studies revealed that Ca 2+ spots arise due to influx through MS channels. In this report, our data indicating the possible significance of LPA as an endogenous factor involved in regulation of mechanotransduction is reviewed. Furthermore, our findings suggest that the Ca 2+ spot is a novel phenomenon occurring as an elementary Ca 2+-influx event through MS channels directly coupled with the initial step in mechanotransduction.

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