FIGURE 2.

Functional assay of CFP/YFP-tagged K_ATP channels. A, ⁸⁶Rb⁺ efflux from untransfected (mock) COSm6 cells and cells expressing SUR1 and Kir6.2 subunits. The graphs show percentages of ⁸⁶Rb⁺ released into the medium as a function of time in the presence of metabolic inhibitors, for one representative experiment. B, representative currents recorded from inside-out membrane patches containing double-tagged Y6.2C co-expressed with SUR1 at −50 mV. The patch was isolated at the arrow and exposed to differing [ATP] as indicated. C, steady-state dependence of membrane current (relative to current in zero ATP) on [ATP] for wild type K_ATP channels and channels formed from Y6.2C + SUR1 subunits (as indicated). The data points represent the means ± S.E. (n = 3 patches). The fitted lines correspond to least squares fits of the Hill equation (relative current = 100/(1 + ([ATP]/K_i)^H), where H = 1.3, and K_i = 12 μm (wild type) and 314 μm (Y6.2C + SUR1). D, representative currents recorded from inside-out membrane patches containing nSUR1Y and cSUR1C co-expressed with Kir6.2 at −50 mV. The patch was exposed to differing [nucleotide] as indicated. In this and the following figures, cartoon representations of different constructs are shown to aid interpretation.