Figure 3.

Effect of histidine mutation on ethanol inhibition of ATP-activated current in rat P2X₄ receptors expressed in Xenopus oocytes. (a) Records showing currents activated by 9, 0.6 and 10.2 μM ATP before, during and after the application of 50 and 100 mM EtOH in three oocytes expressing H140A, H241A or H286A mutated rat P2X₄ receptors, as labelled. (b) Graph plotting average percentage inhibition of the amplitude of current activated by 9, 0.6 and 10.2 μM ATP as a function of EtOH concentration for H140A, H241A and H286A mutants. The dashed curve for the wild-type (WT) receptor is from Figure 1b and is shown for comparison. The magnitude of ethanol inhibition is calculated as percentage inhibition of ATP-activated current; this was determined for each cell studied. As ATP sensitivity was different in wild-type and mutated receptors, an ATP concentration that was close to the EC₄₀ value of each ATP concentration–response curve was used for each mutant (9, 0.6 and 10.2 μM for H140A, H241A and H286A, respectively). Each data point is the average of 5–11 cells; error bars not visible are smaller than the size of the symbols. Values obtained were: IC₅₀=88±10.5 mM; n=1.1±0.2, and E_max=93±6.7% for H140A; IC₅₀=29.6±4.6 mM; n=1.0±0.1, and E_max=100% for H241A; IC₅₀=103.6±9.3 mM; n=1.1±0.2, and E_max=95±6.1% for H286A.