Ca2+ Influx in T Cells: How Many Ca2+ Channels?

Ca2+ signals are critical for T cell function. A number of ion channels regulate Ca2+ influx from the extracellular space in T cells, either by conducting Ca2+ ions or by modulating the membrane potential that provides the driving force for Ca2+ influx (Cahalan and Chandy, 2009; Feske et al., 2012). The best characterized Ca2+ channel in T cells is the Ca2+ release-activated Ca2+ (CRAC) channel, which mediates store-operated Ca2+ entry (SOCE) in response to T cell receptor (TCR) activation and is composed of ORAI and stromal interaction molecules (STIM) family proteins. Several other channels may also mediate Ca2+ influx directly in T cells including members of the transient receptor potential (TRP) family, P2X receptors, and voltage-gated Ca2+ (Cav) channels. Compared to CRAC channels, however, their contribution to TCR-induced Ca2+ influx and immunity is less well defined.