Mutant IP(3) receptors attenuate store-operated Ca(2+) entry by destabilizing STIM–Orai interactions in Drosophila neurons

Store-operated Ca(2+) entry (SOCE) occurs when loss of Ca(2+) from the endoplasmic reticulum (ER) stimulates the Ca(2+) sensor, STIM, to cluster and activate the plasma membrane Ca(2+) channel Orai (encoded by Olf186-F in flies). Inositol 1,4,5-trisphosphate receptors (IP(3)Rs, which are encoded by a single gene in flies) are assumed to regulate SOCE solely by mediating ER Ca(2+) release. We show that in Drosophila neurons, mutant IP(3)R attenuates SOCE evoked by depleting Ca(2+) stores with thapsigargin. In normal neurons, store depletion caused STIM and the IP(3)R to accumulate near the plasma membrane, association of STIM with Orai, clustering of STIM and Orai at ER–plasma-membrane junctions and activation of SOCE. These responses were attenuated in neurons with mutant IP(3)Rs and were rescued by overexpression of STIM with Orai. We conclude that, after depletion of Ca(2+) stores in Drosophila, translocation of the IP(3)R to ER–plasma-membrane junctions facilitates the coupling of STIM to Orai that leads to activation of SOCE.