Calcium-independent phospholipase A(2) mediates store-operated calcium entry in rat cerebellar granule cells

Store-operated Ca2+ entry (SOCE) has been extensively studied in non-neuronal cells, such as glial cells and smooth muscle cells, in which Ca2+-independent phospholipase A(2) (iPLA(2)) has been shown to play a key role in the regulation of SOCE channels. In the present study, we have investigated the role of iPLA(2) for store-operated Ca2+ entry in rat cerebellar granule neurons in acute brain slices using confocal Ca2+ imaging. Depletion of Ca2+ stores by cyclopiazonic acid (CPA) induced a Ca2+ influx, which could be inhibited by SOCE channel blockers 2-aminoethoxy-diphenylborate (2-APB) and 3,5-bistrifluoromethyl pyrazole derivative (BTP2), but not by the voltage-operated Ca2+ channel blocker diltiazem and by the Na+ channel blocker tetrodotoxin. The inhibitors of iPLA(2), bromoenol lactone (BEL) and 1,1,1-trifluoro-2-heptadecanone, and the selective suppression of iPLA(2) expression by antisense oligodeoxynucleotides, inhibited CPA-induced Ca2+ influx. Calmidazolium, which relieves the block of inhibitory calmodulin from iPLA(2), elicited a Ca2+ influx similar to CPA-induced Ca2+ entry. The product of iPLA(2), lysophosphatidylinositol, elicited a 2-APB- and BTP2-sensitive, but BEL-insensitive, Ca2+ influx. Spontaneous Ca2+ oscillations in granule cells in acute brain slices were reduced after inhibiting iPLA(2) activity or by blocking SOCE channels. The results suggest that depletion of Ca2+ stores activates iPLA(2) to trigger Ca2+ influx by the formation of lysophospholipids in these neurons.