Functional significance of human trp1 and trp3 in store-operated Ca(2+) entry in HEK-293 cells.

The Drosophila trp (transient receptor potential) gene appears to encode the Drosophila store-operated channel (SOC), and some mammalian trp homologues have been proposed to encode mammalian SOCs. This study provides evidence for the expression of three trp homologues (Mtrp2, Mtrp3, and Mtrp4) in fibroblasts from wild-type and src knockout mice, and four trp homologues (Htrp1, Htrp3, Htrp4, and Htrp6) in human embryonic kidney (HEK-293) cells based on RT-PCR techniques. In HEK-293 cells stably transfected with a 323-bp Htrp3 antisense construct (Htrp3AS), Northern blot analysis revealed that the expression of a 4-kb transcript was dramatically suppressed in comparison to that observed in cells stably transfected with a short Htrp3 sense construct (Htrp3S). Activity of SOCs, monitored as Ba(2+) influx following Ca(2+) store depletion with thapsigargin, was reduced by 32% in Htrp3AS cells in comparison with Htrp3S cells. Transient transfection of a 369-bp Htrp1 antisense construct in cells stably expressing Htrp3AS induced a higher level of inhibition (55%) of store-operated Ca(2+) entry. These data suggest that Htrp1 and Htrp3 may be functional subunits of SOCs.