Modulation of SCO by P2 receptor agonists and antagonists. (A and B) Bath application of suramin (50 μM) facilitated the SCO but PPADS (10 μM) and MRS2179 (10 μM) were ineffective. Data shown in B are mean ± SEM from 20–40 cells from at least three experiments for each drug. SCO before drug addition were treated as control. Bath application of 100 μM ATP (C) or 30 μM UTP (E) blocked the SCO. UTP inhibited SCO more potently than ATP (G and H). The SCO persisted upon application of 100 μM ATP or 30 μM UTP along with 50 μM suramin (D and F). Data shown in G and H are mean ± SEM for 20–30 neurons from three experiments. (*, P < 0.01; **, P < 0.001).