Figure 5. Trans-stimulation by potential OCT substrates.

A-D, effects of potential OCT substrates on [³H]-MPP⁺ outflow tested in the absence (○) or presence (•) of 0.5 μM desipramine. Desipramine was added to the superfusion buffer 10 min before and during the collection of 4 min fractions. Data are plotted as fractional rates (means ± s.e.m., n = 3 for each individual data point). The following substances were used (applications indicated by bars): 10 mm guanidine (A); 10 mm choline (B); 50 μM amantadine (C); and 10 mm tetraethylammonium Cl⁻ (TEA; D). E, summary of effects of potential OCT substrates on [³H]-MPP⁺ outflow with the experimental protocol shown in A-D. Pattern-filled bars show trans-stimulation by potential substrates: guanidine (Guan) 1.0, 3.0 and 10 mm, n = 6, 12 and 25 individual cultures, respectively; 10 mm choline (n = 6); 50 μM amantadine (Amant, n = 6); 10 mm TEA (n = 17); 100 μM carnitine (n = 9). Filled bars (Des-Guan 10, Des-Choline, Des-Amant and Des-TEA) demonstrate effects of desipramine (added 10 min before and during collection of fractions) on trans-stimulation (n = 6, 6, 6 and 11 individual cultures, respectively). Data are AUC values (means ± s.e.m.), calculated as shown in Fig. 2B. Significantly different from zero: * P < 0.05, ** P < 0.01 (Mann-Whitney U test).