UPTAKE OF 5-HYDROXYTRYPTAMINE IN RAT ISOLATED ATRIA

1. The mode of 5-hydroxytryptamine (5-HT) uptake by the rat isolated atria was studied and compared to noradrenaline (NA) uptake. 2. Rat isolated atria were incubated with C-14-5-HT (46-mu-M) or H-3-NA (0.4-mu-M). After washing, the radioactivity fixed in atria was counted and the total NA, 5-HT and 5-hydroxyindol-3-acetic acid (5-HIAA) atria contents were measured by HPLC. 3. C-14-5-HT uptake was reduced in atria from 6-hydroxydopamine (100 mg/kg, i.p., 48 hr before experiments) or reserpine (2.5 mg/kg, i.p., 24 and 48 hr before experiments) pretreated rats. 4. The incubation of atria with 5-HT (50-mu-M) at the same time as H-3-NA reduced the H-3-NA value fixed. 5. Addition of desipramine (1-mu-M) or hydrocortisone (150-mu-M) before the incubation of atria with C-14-5-HT was without any effect on C-14-5-HT uptake. In contrast. fluvoxamine (1-mu-M) or indalpine (5-mu-M) caused a slight inhibition. 6. These data indicate that 5-HT is taken into the NA storage vesicles within the atria sympathetic nerves. This uptake does not use the NA carrier and involves partly the 5-HT carrier An extraneuronal accumulation was noticed and a part of it is intracellular.