Lysophosphatidic acid (LPA)-mediated Ca2+ mobilization in human SH-SY5Y neu
roblastoma cells does not involve either inositol 1,4,5-trisphosphate (Ins(
1,4,5)P-3)- or ryanodine-receptor pathways, but is sensitive to inhibitors
of sphingosine kinase. This present study identifies Edg-4 as the receptor
subtype involved and investigates the presence of a Ca2+ signaling cascade
based upon the lipid second messenger molecule, sphingosine I-phosphate. Bo
th LPA and direct G-protein activation increase [H-3]sphingosine l-phosphat
e levels in SH-SY5Y cells. Measurements of Ca-45(2+) release in premeabiliz
ed SH-SY5Y cells indicates that sphingosine I-phosphate, sphingosine, and s
phingosylphosphorylcholine, but not N-acetylsphingosine are capable of mobi
lizing intracellular Ca2+. Furthermore, the effect of sphingosine was atten
uated by the sphingosine kinase inhibitor dimethylsphingosine, or removal o
f ATP. Confocal microscopy demonstrated that LPA stimulated intracellular C
a2+ "puffs," which resulted from an interaction between the sphingolipid Ca
2+ release pathway and Ins(1,4,5)P-3 receptors. Down-regulation of Ins(1,4,
5)P-3 receptors uncovered a Ca2+ response to LPA, which was manifest as a p
rogressive increase in global cellular Ca2+ with no discernible foci. We su
ggest that activation of an LPA-sensitive Edg-4 receptor solely utilizes th
e production of intracellular sphingosine l-phosphate to stimulate Ca2+ mob
ilization in SB-SY5Y cells. Unlike traditional Ca2+ release processes, this
novel pathway does not require the progressive recruitment of elementary C
a2+ events.