Receptor-mediated activation of a Cl^- current by LPA and S1P in cultured corneal keratocytes

PURPOSE. This study was designed to examine the effects of lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) on Cl^- currents (ICl_LPA) in cultured corneal keratocytes isolated from the corneas of New Zealand White rabbits. METHODS. ICl_LPA and resting voltages were recorded with the amphotericin perforated-patch technique. Phenotype was determined with antibodies to α-smooth muscle actin. RESULTS. Keratocytes cultured in serum have a phenotype (myofibroblast) and ionic currents similar to those of keratocytes isolated directly from corneas during wound healing. LPA and S1P both activated ICl_LPA in a dose-dependent manner, and the LPA receptor-specific antagonist dioctyl-glycerol pyrophosphate (DGPP) blocked the LPA response, but not the S1P response. In addition, a relatively inactive form of LPA (LPA 8:0) was relatively ineffective in activating ICl_LPA. Activation of ICl_LPA significantly depolarized the cells, and this depolarization was reversed by blocking ICl_LPA with 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) or 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). CONCLUSIONS. These results demonstrate that activation of ICl_LPA by LPA in cultured corneal keratocytes is receptor mediated and that ICl_LPA can also be activated by S1P. From a functional standpoint, this work confirms that the current, which is typically thought of as purely volume-activated, can be activated through a receptor. In addition, activation of ICl_LPA results in depolarization of the keratocyte. Finally, this work demonstrates that cultured corneal keratocytes can act as a model for the study of ion channel function in keratocytes during corneal wound healing.