Figure 2.

Principle of cell-based assay of K⁺ transport. (a) K⁺ efflux measurement method showing accumulation of K⁺ in an initially K⁺-free extracellular solution resulting from K⁺ efflux from cells. (b) Single measurement of ATP-induced K⁺ efflux in HT-29 cells (cell density 6.3 × 10⁵ cells/cm², cell/bath volume ratio 0.27). (c) K⁺ efflux in HT-29 cells under control conditions, and after incubations with a K⁺ ionophore (valinomycin) or K⁺/H⁺ antiporter (nigericin). Cells were preincubated in high K⁺ buffer where indicated. Each data point is mean ±SE (n ) 3). (d) Deduced K⁺ efflux rates, d[K⁺]/dt, from data in (c). *P < 0.05.