2,3-Butanedione monoxime (BDM) inhibition of delayed rectifier DRK1 (Kv2.1) potassium channels expressed in Xenopus oocytes

DRK1 is a cloned K⁺ channel from rat brain with consensus sites for protein kinase-dependent phosphorylation that might be expected to be functionally regulated by phosphorylation. 2,3-Butane-dione-monoxime (BDM) chemically removes phosphate groups from many proteins, and its action on DRK1 channels was examined after expression of DRK1 cRNA in Xenopus oocytes. In two-microelectrode voltage-clamp experiments, the application of BDM to the bath inhibited DRK1 current (k₁ = 16.6 mM, H = 0.96) rapidly and reversibly, with a time course similar to the time course of solution change within the bath. DRK1 current was inhibited at all potentials; the time course of current activation, deactivation and inactivation were unaffected by BDM. In inside-out patch-clamp experiments, the application of BDM to the cytoplasmic surface similarly inhibited channel activity rapidly and reversibly (k₁ = 10.7 mM, H = 1.01) in the absence of rephosphorylating substrates. These results are inconsistent with a phosphatase effect, because such an effect should be irreversible in cell-free, ATP-free patches. Instead, the results suggest that BDM can inhibit DRK1 channels directly from inside or outside of the membrane.