Figure 6.

K⁺ tolerance correlates with sequestration. (A) Growth sensitivity to extracellular KCl. The isogenic set of wild-type and null mutants was grown in synthetic APG medium supplemented with KCl as indicated. Growth was measured after 18 h and expressed as percent of growth in 1 mM KCl. (B) Uptake of ⁸⁶Rb into intact and permeabilized cells. The mutant nhx1Δnha1Δ strain was transformed with plasmid expressing wild-type NHX1 (NHX1) or empty vector (Δnhx1) and uptake of ⁸⁶Rb into intact or Cu²⁺-treated (plasma membrane permeabilized) cells was quantitated as described in Materials and Methods. (C) Efflux of ⁸⁶Rb from intact and permeabilized cells. Yeast strains described in B were preloaded with ⁸⁶Rb, CuSO₄ was added to one-half of the preloaded culture (+Cu²⁺), and at intervals, cells were collected by rapid filtration and the remaining radioactivity determined by liquid scintillation counting of filters. Efflux is presented as percent of cell-associated radioactivity measured immediately before Cu²⁺ addition. Means and calculated SEs are plotted from three independent experiments.