Figure 5. a, Summary of effects of DTT (10 mm, 12 min) on αβmeATP-evoked currents recorded from cells coexpressing different combinations of wild-type or single mutant P2X2 and P2X3 receptors (n = 3-9 cells for each combination). Filled bars represent forms with cysteines in both subunits. Actual currents in those seven combinations in which DTT had no effect included the following (pA ± SEM for the number of cells in parentheses): P2X2[V48C] with P2X3[V42C], 1244 ± 358 (4); P2X2[I328C] with P2X3[I319C], 404 ± 61 (4); P2X2[V48C] with wild-type P2X3, 471 ± 122 (4); P2X2[I328C] with wild-type P2X3, 840 ± 215 (4); wild-type P2X2 with P2X3[V42C], 1399 ± 468 (3); wild-type P2X2 with P2X3[I319C], 692 ± 276 (4); and wild-type P2X2 with wild-type P2X3, 924 ± 258 (4). b, Schematic representation of subunit arrangements for forms with cysteines in both subunits, assuming that the channel is a trimer. Left, Channels containing one P2X3 subunit (black). Right, Channels containing one P2X2 subunit (gray). TM1 and TM2 of each subunit are indicated; cysteines that have been introduced are depicted by small filled circles. The arrows indicate the disulfides that have formed, based on an effect of dithiothreitol on the expressed currents.