Fig. 4.

ATP induces calcium influx in human kidney proximal tubule (HK-2) cells via P2X7 receptor activation. Representative relative delta fluorescent unit (RFU) tracing of Fluo-4 (A) over time as an indicator of calcium influx as well as averaged maximal delta RFU (B) in HK-2 cells (N = 4). HK-2 cells were treated with vehicle or with 50 μM iso-PPADS (a P2X receptor antagonist) 15 min before 1 mM ATP treatment. *P < 0.05 vs. vehicle group. Red arrow indicates when ATP or vehicle was injected to the cells. C: averaged maximal delta RFU (normalized to vehicle) indicating calcium influx in HK-2 cells treated with ATP (500 µM or 1 mM), ATPγS (500 µM), and BzATP (50 µM, a selective P2X7 receptor agonist). Some cells were pretreated with A804598 (a P2X7 receptor antagonist, 20 µM) before ATP treatment. Calcium ionophore (10 µM) was used as a positive control. ATP-mediated calcium influx in HK-2 cells is mediated by P2X7 receptor activation as a selective P2X7 antagonist, A804598, blocked and a selective P2X7 agonist, BzATP, mimicked the effects of ATP on calcium influx in HK-2 cells. *P < 0.01 vs. vehicle. #P < 0.05 vs. ATP 1 mM. N = 4–8.