LYSOPHOSPHATIDIC ACID DEPLETES INTRACELLULAR CALCIUM STORES DIFFERENTFROM THOSE MEDIATING CAPACITATIVE CALCIUM-ENTRY IN C6 RAT GLIOMA-CELLS

Lysophosphatidic acid (LPA) functions as an extracellular lipid mediat or stimulating phospholipase C and affecting the structure of the cyto skeleton in several cell types. In rat glioma C6 cells, LPA mobilizes calcium from intracellular calcium stores and reverts morphological ch anges induced by elevated cytosolic cAMP-concentrations. Here we show that LPA-stimulation of C6 cells loaded with the calcium-sensitive flu orescent dye indo-1 results in calcium release from a subset of intrac ellular calcium stores that are not sensitive to the tumor promoter th apsigargin and do not overlap with calcium stores depleted during puri nergic receptor stimulation with ATP. Furthermore, depletion of LPA-se nsitive calcium stores does not induce capacitative calcium entry from the extracellular space into the cytosol to the same extent as ATP. T hese results indicate that inositol phosphate signaling induced by LPA or ATP may differ in kinetics or in spatial organisation within the c ell. This may represent a possible explanation for the previous observ ation that only LPA, but not other calcium-mobilizing agonists, revert s cAMP-induced changes in the cytoskeletal organization in C6 cells. ( C) 1997 Wiley-Liss, Inc.