FIGURE 2.

Adenine nucleotide sensitivity of wild-type Kir6.2+SUR1 channels. (A, B, and C) Inward currents measured in the absence of Mg²⁺ were progressively suppressed by increasing concentrations of ATP, ADP, and AMP with the IC₅₀ near 12 μM, 120 μM, and 1.85 mM, respectively. On average, ADP was 8- to 10-fold less potent than ATP in blocking the channel, and AMP 140-fold less potent. (D) Plot of ATP (•), ADP (○), and AMP (▴) sensitivity for Kir6.2+SUR1 in the absence of Mg²⁺. The data points were fit with the equation y = 1/(1 + (k/[ATP])ⁿ), which yielded k = 12.5 μM for ATP (n = 5), k = 115 μM (n = 5) for ADP, and k = 1.85 mM for AMP (n = 5). The three Hill coefficients were close to unity.