Figure 1 - Coupling models for activation of store-operated channels (SOCs).

a, 'Chemical coupling', involving the release of a diffusible calcium influx factor (CIF) from the ER in response to release detected by a presumed luminal calcium sensor. b, 'Direct physical coupling', involving a direct interaction between components of the ER and PM, shown hypothetically as a complex between calcium release and entry channels. c, d, Two variations on the physical coupling theme. 'Induced coupling' (c), in which a dynamic process concomitant with store-depletion induces the formation of new conformationally coupled ER–PM junctions. d, 'Spatial coupling', in which a spatially close organization exists between ER and PM, permitting short-range signalling to effect SOC activation within a restricted space (shaded).