Naunyn-Schmiedeberg's Arch Pharmacol (1994) 350:130-142 Nau nyn-Sch m iedeberg's Archivesof Pharmacology © Springer-Verlag 1994 Uptake of 3H-catecholamines by rat liver cells occurs mainly through a system which is distinct from uptakea or uptake/* E Martel** I. Azevedo, W. Osswald Institute of Pharmacology and Therapeutics, Faculty of Medicine, P-4200 Porto, Portugal Received: 17 January 1994/Accepted: 14 March 1994 Abstract. Isolated rat hepatocytes were incubated with 200nmol/1 3H-(-)-noradrenaline or 50nmol/1 3H- (-)-adrenaline for 15 rain, in Krebs-Henseleit solution at 37°C, gassed with 95% 02 5% CO 2. Monoamine ox- idase and catechol-O-methyl transferase were inhibited with pargyline (500gmol/1) and Ro 01-2812 (3,5-dinitropyrocatechol; 2 gmol/1), respectively. Total ra- dioactivity present in the cells, which corresponded most- ly to intact 3H-amine, was measured. The content of 3H-noradrenaline increased with time of incubation, a plateau having been reached after 15 rain of incubation. After 15min of incubation, the cell:medium ratio for 3H-noradrenaline and 3H-adrena- line was 0.6-0.7. Desipramine (an inhibitor of the neuro- nal uptake of catecholamines - uptake1; 1 gmol/1) did not affect the 3 uptake of either H-noradrenaline or 3H- adrenaline into hepatocytes. Corticosterone (an inhibitor of the extraneuronal uptake of catecholamines - uptake2; 40 ~tmol/1) slightly inhibited (by 28%) the uptake of 3H- adrenaline, and did not significantly reduce 3H-nor- adrenaline uptake. Probenecid (an inhibitor of the renal transport of organic anions; 100 gmol/1) did not influ- ence the amount of either 3H-noradrenaline or 3H- adrenaline in hepatocytes. Cyanine 863 (an inhibitor of the renal transport of organic cations; 10 gmol/1) de- creased by 62% the uptake of 3H-adrenaline into cells but did not significantly affect 3H-noradrenaline uptake. Bilirubin (a substrate of a hepatic transport for organic anions; 200gmol/1) produced a significant increase (50%) in the amount of 3H-noradrenaline and 3H-adren- aline present in the cells. When isolated hepatocytes were incubated in a sodium-free medium (sodium being re- placed by choline or lithium) there was a very marked in- hibition of 3H-noradrenaline and 3H-adrenaline uptake Abbreviations: COMT, catechol-O-methyl transferase; MAO, mono- amine oxidase; RTOC, renal transport of organic cations * Supported by Programa STRIDE (STRDA/P/SAU/259/92) ** PhD student with a grant from JNICT (Programa Ci~ncia) Correspondence to: E Martel at the above address (by 85-97%). An increase in potassium content of the medium (from 6.6 to 50 mmol/1) did not affect the uptake of either 3H-amine into isolated cells. In conclusion, the uptake of catecholamines by isolat- ed liver cells possesses characteristics that distinguish it from the classic uptake systems for catecholamines (up- take1 and uptake2): (1) it is sodium-dependent but not affected by desipramine; (2) it is only slightly sensitive to corticosterone and not affected by potassium-induced de- polarization; (3) it is partially sensitive to cyanine 863. Moreover, the increase of 3H-amine content in the cells in the presence of bilirubin suggests the possibility of cat- echolamines being excreted from the hepatocytes through the bilirubin transporter. Key words: Hepatocyte - Catecholamines - Uptake 1 - Uptake 2 - Renal organic cation transport - Bilirubin Introduction Removal of catecholamines from the synaptic cleft or blood stream is accomplished by "metabolizing systems", a combination of an uptake system with subsequent in- tracellular metabolism by monoamine oxidase (MAO) and/or catechol-O-methyl transferase (COMT), responsi- ble for the termination of biological actions of these amines (Trendelenburg 1990). Two uptake systems have been described for noradren- aline: 1) uptakes, a desipramine-sensitive mechanism present in adrenergic nerve terminals (for review see Graefe and B6nisch 1988) and in some non-neuronal tis- sues such as the rat pulmonar endothelium (Bryan-Lluka et al. 1992), uterus and placenta (Kennedy and de la Lande 1988) and heart Purkinje fibres (Azevedo et al. 1983), and the glandular epithelium of endometrium (Kennedy and de la Lande 1986), fibroblasts of dental pulp (Parker et al. 1987) and oral and nasal mucosa (de la Lande et al. 1987) of the rabbit and astroglial cells in