FIGURE 5.

Adenine nucleotide sensitivity of R50G, K185Q, R192C, and R201A mutants coexpressed with SUR1, compared with wild-type Kir6.2+SUR1 channels. As already shown with wild-type channels, the ADP sensitivity was ninefold lower than ATP sensitivity and AMP 100-fold lower. As compared to wild-type, K185Q mutation decreased the ATP and ADP sensitivity by 35-fold, but had minimal effect on AMP sensitivity. In contrast, the R192C mutation had similar effects on ATP, ADP, and AMP sensitivities and caused a 12- to 15-fold decrease. R50G behaved like K185Q and decreased the ATP and ADP sensitivity by ∼120- to 140-fold, but the AMP sensitivity decreased by only 11-fold. R201A behaved like R192C and decreased the sensitivity to all three nucleotide. The sensitivity to ATP and ADP decreased by 60-fold. The AMP sensitivity with R201A+SUR1 could not be measured accurately, but 20 mM AMP caused 15% channel inhibition. Thus, assuming a Hill coefficient of 1, the IC₅₀ for channel inhibition by AMP would be close to 100 mM and the AMP sensitivity decreased by a similar amount (60-fold).