Channels 129 I CRAC mediates SOCE in microglia [Channels 3:2, 129-139; March/April 2009]; ©2009 Landes BioscienceCa 2+ signaling plays a central role in microglial activation, and several studies have demonstrated a store-operated Ca 2+ entry (SOCE) pathway to supply this ion. Due to the rapid pace of discovery of novel Ca 2+ permeable channels, and limited electrophysiological analyses of Ca 2+ currents in microglia, characterization of the SOCE channels remains incomplete. At present, the prime candidates are 'transient receptor potential' (TRP) channels and the recently cloned Orai1, which produces a Ca 2+ -release-activated Ca 2+ (CRAC) current. We used cultured rat microglia and real-time RT-PCR to compare expression levels of Orai1, Orai2, Orai3, TRPM2, TRPM7, TRPC1, TRPC2, TRPC3, TRPC4, TRPC5, TRPC6 and TRPC7 channel genes. Next, we used Fura-2 imaging to identify a store-operated Ca 2+ entry pathway that was reduced by depolarization and blocked by Gd 3+ , SKF-96365, diethylstilbestrol (DES), and a high concentration of 2-aminoethoxydiphenyl borate (50 μM 2-APB). The Fura-2 signal was increased by hyperpolarization, and by a low concentration of 2-APB (5 μM), and exhibited Ca 2+ -dependent potentiation. These properties are entirely consistent with Orai1/CRAC, rather than any known TRP channel and this conclusion was supported by patch-clamp electrophysiological analysis. We identified a store-operated Ca 2+ current with the same properties, including high selectivity for Ca 2+ over monovalent cations, pronounced inward rectification and a very positive reversal potential, Ca 2+ -dependent current potentiation, and block by SKF-96365, DES and 50 μM 2-APB. Determining the contribution of Orai1/CRAC in different cell types is crucial to future mechanistic and therapeutic studies; this comprehensive multi-strategy analysis demonstrates that Orai1/CRAC channels are responsible for SOCE in primary microglia.