Effect of other Mg-nucleotides. (A) Mean increase in Kir6.2-G334D/SUR1 current in the presence of different nucleotides (refer to Materials and methods). White bar, 1 mM MgATP (n = 13); pale gray bar, 1 mM MgATPγS (n = 6); dark gray bar, 1 mM MgADP (n = 7); black bar, 1 mM MgAMP-PNP (n = 6); crosshatched bar, 1 mM MgAMP-PNP plus 1 mM MgATP (n = 6). ***, P < 0.001 (against MgATP). (B) Mean time constants (τ) of current activation (τ_ON-1 and τ_ON-2) and deactivation (τ_OFF) by MgATP (white bars, n = 13), MgATPγS (pale gray bars, n = 6), and MgADP (dark gray bars, n = 7). *, P < 0.5; ***, P < 0.001 (against MgATP). (C) Time course of current activation and deactivation by 1 mM MgADP (top) and 1 mM MgATP (bottom). Nucleotide application is indicated by the bar, and the dotted line represents the zero current level. The white lines are the best fit of one (MgADP) or two (MgATP) exponential components for activation (⁠$A1*e−t/τ1+A2*e−t/τ2$⁠) and one for deactivation (A*e^−t/τ). For MgADP: A_ON-1 = 680 pA, τ_ON-1 = 330 ms; A_OFF = 680 pA, τ_OFF = 1,320 ms. For MgATP: A_ON-1 = 490 pA, τ_ON-1 = 730 ms; A_ON-2 = 180 pA, τ_ON-2 = 4,060 ms; A_OFF = 670 pA; τ_OFF = 1,835 ms.