The Drosophila retinal-specific protein, TRP (transient receptor potential), is the founding member of a family of store-operated channels (SOCs) conserved from C. elegans to humans. In vitro studies indicate that TRP is a SOC, but that the related retinal protein, TRPL, is constitutively active. In the current work, we report that coexpression of TRP and TRPL leads to a store-operated, outwardly rectifying current distinct from that owing to either TRP or TRPL alone. TRP and TRPL interact directly, indicating that the TRP-TRPL-dependent current is mediated by heteromultimeric association between the two subunits. We propose that the light-activated current in photoreceptor cells is produced by a combination of TRP homo- and TRP-TRPL heteromultimers.