Polycystin-1 (PC1) is a membrane protein expressed in tubular epithelia of developing kidneys and in other ductal structures. Recent studies indicate this protein to be putatively important in regulating intracellular Ca2+ levels in various cell types, but little evidence exists for kidney epithelial cells. Here we examined the role of the PC1 cytoplasmic tail on the activity of store operated Ca2+ channels in human kidney epithelial HEK-293 cell line. Cells were transiently transfected with chimeric proteins containing 1-226 or 26-226 aa of the PC1 cytoplasmic tail fused to the transmembrane domain of the human Trk-A receptor: TrkPC1 wild-type and control Trk truncated peptides were expressed at comparable levels and localized at the plasma membrane. Ca2+ measurements were performed in cells co-transfected with PC1 chimeras and the cytoplasmic Ca2+-sensitive photoprotein aequorin, upon activation of the phosphoinositide pathway by ATP, that, via purinoceptors, is coupled to the release of Ca2+ from intracellular stores. The expression of TrkPC1 peptide, but not of its truncated form, enhanced the ATP-evoked cytosolic Ca2+ concentrations. When Ca2+ assays were performed in HeLa cells characterized by Ca2+ stores greater than those of HEK-293 cells, the histamine-evoked cytosolic Ca2+ increase was enhanced by TrkPC1 expression, even in absence of external Ca2+. These observations indicate that the C-terminal tail of PC1 in kidney and other epithelial cells upregulates a Ca2+ channel activity also involved in the release of intracellular stores. (C) 2003 Elsevier Science (USA). All rights reserved.