Figure 1.

Effects of extracellular UTP on α,β-meATP-induced currents in HEK293 cells permanently transfected with the human P2X₃ receptor (HEK293-hP2X₃ cells). The whole-cell variant of the patch-clamp method was used to record membrane currents. Cells were held at -60 mV. Both α,β-meATP and UTP were locally applied by means of a rapid superfusion system. α,β-meATP was applied six times for 1 s each with an interval of 5 min between two applications, with the exception of the second and third application, which were spaced apart by 10 min. Superfusion with UTP started 5 min (A, B, Ca) or variable intervals before the third application of α,β-meATP (1-5 min; Cb) and was stopped immediately after the fourth application of α,β-meATP. Aa, Original tracing recorded with a patch pipette filled with GTP (300 μm)-containing solution. UTP (3 μm) did not alter the α,β-meATP (3 μm) current. Ab, Mean ± SEM of eight experiments similar to that shown in Aa. Ba, Original tracing recorded with a patch pipette filled with solution containing GDP-β-S (3 μm) instead of GTP. UTP (3 μm) markedly facilitated the α,β-meATP (3 μm)-induced current. Bb, Mean ± SEM of seven experiments similar to that shown in Ba. ^*p < 0.05, statistically significant difference from the preceding column. Ca, Concentration-response relationship for the potentiating effect of UTP on the α,β-meATP (3 μm)-induced current. Mean ± SEM of four to eight experiments. Cb, Dependence of the potentiating effect of UTP (3 μm) on its superfusion time before the application of α,β-meATP. Mean ± SEM of four to seven experiments. ^*p < 0.05, statistically significant difference from 100%.