Lysophosphatidic acid-induced Ca(2+) mobilization in the neural retina of chick embryo

Lysophosphatidic acid (LPA) plays various roles in the regulation of cell growth as a lipid mediator. We studied the effect of LPA on intracellular Ca(2+) concentration (Ca2+]i) with Fura-2 in the neural retina of chick embryo during neurogenesis. Bath application of LPA (1-100 microM) to the embryonic day 3 (E3) chick retina caused an increase in Ca2+](i) in a dose-dependent manner, with an EC(50) value of 9.2 microM. The Ca(2+) rise was also evoked in a Ca(2+)-free medium, suggesting that release of Ca(2+) from intracellular Ca(2+) stores (Ca(2+) mobilization) was induced by LPA. U-73122, a blocker of phospholipase C (PLC), inhibited the Ca(2+) rise to LPA. Pertussis toxin partially inhibited the Ca(2+) rise to LPA, indicating that G(i)/G(o) protein was at least partially involved in the LPA response. The developmental profile of the LPA response was studied from E3 to E13. The Ca(2+) rise to LPA declined drastically from E3 to E7, in parallel with decrease in mitotic activity of retinal progenitor cells. The signal transduction pathway and developmental profile of the Ca(2+) response to LPA were the same as those of the Ca(2+) response to adenosine triphosphate (ATP), which enhances the proliferation of retinal progenitor cells. The coapplication of LPA with ATP resulted in enhancement of Ca(2+) rise in the E3 chick retina. Our results show that LPA induces Ca(2+) mobilization in the embryonic chick retina during neurogenesis.