Lysophosphatidic acid‐induced Ca2+ 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 Ca²⁺ concentration ([Ca²⁺]_i) with Fura‐2 in the neural retina of chick embryo during neurogenesis. Bath application of LPA (1–100 μM) to the embryonic day 3 (E3) chick retina caused an increase in [Ca²⁺]_i in a dose‐dependent manner, with an EC₅₀ value of 9.2 μM. The Ca²⁺ rise was also evoked in a Ca²⁺‐free medium, suggesting that release of Ca²⁺ from intracellular Ca²⁺ stores (Ca²⁺ mobilization) was induced by LPA. U‐73122, a blocker of phospholipase C (PLC), inhibited the Ca²⁺ rise to LPA. Pertussis toxin partially inhibited the Ca²⁺ 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 Ca²⁺ 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 Ca²⁺ response to LPA were the same as those of the Ca²⁺ response to adenosine triphosphate (ATP), which enhances the proliferation of retinal progenitor cells. The coapplication of LPA with ATP resulted in enhancement of Ca²⁺ rise in the E3 chick retina. Our results show that LPA induces Ca²⁺ mobilization in the embryonic chick retina during neurogenesis. © 1999 John Wiley & Sons, Inc. J Neurobiol 41: 495–504, 1999