Novel effect of N-palmitoyl-L-serine phosphoric acid on cytosolic Ca2+ levels in human osteoblasts

The effect of N-palmitoyl-L-serine phosphoric acid (L-NASPA), which has been used as an inhibitor of lysophosphatidic acid receptors, on intracellular Ca2+ concentration (Ca2+]i) in human osteosarcoma MG63 cells was measured by using fura-2. L-NASPA (0.1-10 microM) caused a rapid and transient plateau Ca2+]i rise in a concentration-dependent manner (EC50=0.5 microM). The L-NASPA-induced Ca2+]i rise was partly reduced by removal of extracellular Ca2+ but was not altered by L-type voltage-gated Ca2+ channel blockers. In Ca2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, induced a Ca2+]i rise, after which the increasing effect of L-NASPA on Ca2+]i was completely inhibited; also, pretreatment with L-NASPA partly reduced thapsigargin-induced Ca2+]i rise. U73122, an inhibitor of phospholipase C, abolished histamine (but not L-NASPA)-induced Ca2+]i rise. Overnight incubation with 1 microM L-NASPA did not affect cell proliferation, but 10-20 microM L-NASPA exerted 4% and 15% inhibition, respectively. Collectively, L-NASPA rapidly increased Ca2+]i in MG63 cells by evoking both extracellular Ca2+ influx and intracellular Ca2+ release, and is cytotoxic at higher concentrations.