Figure 4.

Trans-stimulation and activation of MPP⁺ uptake into 293 cells expressing EMTr in K⁺ buffer. Shown is mean±s.e.mean (n=3) of specific uptake. Specific uptake is total uptake minus non-specific uptake. Non-specific uptake (0.58±0.01 pmol min⁻¹ mg protein⁻¹) was measured in parallel assays with 10 μmol l⁻¹ disprocynium24 both in preincubation and uptake buffers to inhibit EMTr. Stably transfected cells grown in dishes were preincubated for 24 min in K⁺ buffer (control), supplemented where indicated with 1 mmol l⁻¹ of unlabelled MPP⁺ for loading. After washing three times with each 4 ml ice-cold buffer to remove substrate from extracellular space, uptake of ³H-MPP⁺ (0.1 μmol l⁻¹, 1 min) in K⁺ buffer was measured. Parallel assays were performed with the addition of 50 μmol l⁻¹ unlabelled DMPBI solely to uptake buffer.