Figure 2.

Overexpression of PIP5K:WT decreases the sensitivity of K_ATP channels to inhibition by ATP. (A) Representative wild-type K_ATP channel currents recorded in inside-out membrane patches from control cells, cells overexpressing PIP5K:WT (WT Kinase), or cells overexpressing PIP5K:Δ1–238 (ΔN Kinase). Currents were recorded at −50 mV and are shown as upward deflections. The patch was exposed to differing [ATP] as indicated by the bars above the record. (B) K_1/2 estimated for wild-type K_ATP channels in cells overexpressing PIP5K:WT or cells overexpressing PIP5K:Δ1–238, from fits of the Hill equation {I_rel = 1/[1 + ([ATP]/K_1/2)^H]}, with I_rel being the current in ATP, relative to the current in the absence of ATP. The Hill coefficient H was fixed at 1.3. Each data point represents the average of 15–26 patches. The error bar is the SEM. (Inset) PIP₂ levels measured in control cells, cells overexpressing PIP5K:WT, or cells overexpressing PIP5K:Δ1–238. Results represent the means ± SD of triplicate determinations.