FIGURE 7.

Diazoxide does not further increase ⁸⁶Rb⁺ efflux by increasing activity of channels already activated by metabolic inhibition. A, schematic of the rubidium efflux experiment. COSm6 cells expressing WT or various mutant channels were loaded with ⁸⁶Rb⁺ overnight without CBZ rescue (only 0.1% DMSO vehicle was added to the medium). Metabolic inhibition and efflux were carried out in the presence of 200 μm diazoxide. B, efflux over a 40-min period is expressed as percentage of total ⁸⁶Rb⁺ counts. Note that diazoxide did not significantly enhance efflux activity of WT or mutant channels present in the membrane, suggesting that existing channels were already maximally activated by metabolic inhibition. Each bar represents mean ± S.E. (error bars) of three independent experiments. No statistically significant difference was found between the two treatment groups in all mutants by Student's t test.