COEXPRESSION OF DROSOPHILA TRP AND TRP-LIKE PROTEINS IN XENOPUS OOCYTES RECONSTITUTES CAPACITATIVE CA2+ ENTRY

Capacitative Ca2+ entry is a component of the inositol-lipid signaling in which depletion of inositol 1,4,5-trisphosphate (InsP(3))-sensitiv e Ca2+ stores activates Ca2+ influx by a mechanism that is still unkno wn. This pathway plays a central role in cellular signaling, which is mediated by many hormones, neurotransmitters, and growth factors, Stud ies of Drosophila photoreceptors provided the first putative capacitat ive Ca2+ entry mutant designated transient receptor potential (trp) an d a Drosophila gene encoding TRP-like protein (trpl), It is not clear how the Ca2+ store depletion signal is relayed to the plasma membrane and whether both TRP and TRPL participate in this process. We report h ere that coexpressing Drosophila TRP and TRPL in Xenopus oocytes syner gistically enhances the endogenous Ca2+-activated Cl- current and prod uces a divalent inward current, Both of these currents are activated b y Ca2+ store depletion. In the absence of Ca2+, Mg2+ is the main charg e carrier of the divalent current, This current is characterized by la nthanum sensitivity and a voltage-dependent blocking effect of Mg2+, w hich Is relieved at both hyperpolarizing (inward rectification) and de polarizing (outward rectification) potentials. The store-operated diva lent current is neither observed in native oocytes nor in oocytes expr essing either TRP or TRPL alone, The production of this current implic ates a cooperative action of TRP and TRPL in the depletion-activated c urrent.