Lysophosphatidic Acid Induces a Sustained Elevation of Neuronal Intracellular Calcium

Abstract: Lysophosphatidic acid (LPA) is a lipid biomediator enriched in the brain. A novel LPA-induced response in rat hippocampal neurons is described herein, namely, a rapid and sustained elevation in the concentration of free intracellular calcium (Ca²⁺]_i). This increase is specific, in that the related lipids phosphatidic acid and lysophosphatidylcholine did not induce an alteration in Ca²⁺]_i. Moreover, consistent with a receptor-mediated process, there was no further increase in Ca²⁺]_i after a second addition of LPA. The LPA-induced increase in Ca²⁺]_i required extracellular calcium. However, studies with Cd²⁺, Ni²⁺, and nifedipine and nystatin-perforated patch clamp analyses did not indicate involvement of voltage-gated calcium channels in the LPA-induced response. In contrast, glutamate appears to have a significant role in the LPA-induced increase in Ca²⁺]_i, because this increase was inhibited by NMDA receptor antagonists and α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptor antagonists. Thus, LPA treatment may result in an increased extracellular glutamate concentration that could stimulate AMPA/kainate receptors and thereby alleviate the Mg²⁺ block of the NMDA receptors and lead to glutamate stimulation of an influx of calcium via NMDA receptors.