The PDZ scaffold protein INAD abolishes apparent store-dependent regulation of the light-activated cation channel TRP

SPECIFIC AIMSPhototransduction in fly eyes is mediated by a multiprotein complex assembled by the PDZ scaffold protein INAD. Phospholipase C, eye-specific protein kinase C, and TRP cation channel are tethered to INAD. To investigate whether the interaction with the scaffold protein INAD has any effect on the function of the bound proteins, we studied the activation properties of TRP in the presence and absence of INAD.PRINCIPAL FINDINGSHeterologously expressed Calliphora TRP was characterized as a cation channel activated by protocols applied to study store-activated regulation of cation channels. The application of thapsigargin in the presence of extracellular Ca2+ resulted in a twofold increase in intracellular Ca2+ (Fig. 1⤻ A). A twofold increase in [Ca2+]i was also detected after depletion of intracellular Ca2+ stores by preincubation with thapsigargin in the presence of EGTA and subsequent readdition of Ca2+ (Fig. 1B⤻ ). Thus, the activation mechanisms for Ca2+ entry into Sf9 cells expressing Calliph...