Fig. 6.

Ouabain-resistant influx and efflux measured through ⁸⁶Rb movement. A: K⁺ and Rb⁺ influx was measured in NKCC1 cRNA-injected oocytes in the presence and absence of 20 μM bumetanide in isosmotic or hyperosmotic media containing either 4 mM KCl or 4 mM RbCl. Bars represent means ± SE (n = 20–25 oocytes). B: oocytes injected with NKCC1 cRNA were preloaded with ⁸⁶Rb, and washout kinetics was measured in hyperosmotic solutions containing 4 mM K⁺ or 4 mM Rb⁺. After reconstituting the content of ⁸⁶Rb in the oocytes at each time point and plotting the data [exponential decrease: ⁸⁶Rb(t) = ⁸⁶Rb_t=0 e^−kt] in semi-logarithmic form, the first-order rate constant for K⁺ efflux in the absence (○) or presence of 20 μM bumetanide (■) was measured as the slope of the linear component. Arrow indicates a change in external solution. Experiments were done in duplicate.