AM546 activated the K69C receptor.

<p>A–B: Sample traces from oocytes expressing either wild type rP2X2 (WT) or K69C as they were exposed to 50 µM AM546 for 5 minutes and then washed with recording solution. The horizontal dotted lines indicate the pretreatment holding current levels. The vertical dashed lines to the right of each trace indicate the difference in holding current 2 min after washout from the holding current before exposure to the drug. For wild type the change was so small that the whiskers obscure the amplitude of the dashed line. C: AM546 treatment caused K69C expressing oocytes to become responsive to zinc and acidic pH in the absence of exogenous ATP, but had no effect on responses of wild type receptors. Note the change in holding current after AM546 treatment in K69C expressing oocytes but not wild type oocytes (vertical dashed lines to the right of the traces). D–E: Quantitative characterization of a series of oocytes studied as in C, as well as control oocytes exposed to the vehicle alone (0.5% DMSO) (N = 4–8). Asterisks indicate a statistically significant difference from the DMSO control tested on the same construct.