Figure 4.

ORK1-dependent yeast cell growth and K⁺ uptake are inhibited barium. (a) Inhibition of ORK1 or KAT1-dependent yeast growth by three common K⁺ channel blockers. CY162 cells (10⁵) expressing the designated channels were plated in RPD medium with 1 mM KCl. Sterile filter disks were placed on the surface of the agar and saturated with 20 μl of solutions containing chloride salts of barium (5 μmol), TEA (20 μmol), or cesium (2 μmol). The plates were incubated for 36 hr at 30°C. (b) Uptake of rubidium by CY162 cells carrying pRAD-ORK1 (•) or pRAD (○) at various concentrations of unlabeled rubidium chloride. (c) Inhibition of rubidium uptake by barium (○) or TEA (•) at 50 μM rubidium chloride. The solid curve is fitted to the data according to (1 + [blocker]/K_i)⁻¹, where K_i is the equilibrium dissociation constant; under these conditions 0.15 mM external barium decreases flux ≈50%.