Evidence for uptake2-mediated O-methylation of noradrenaline in the human amnion FL cell-line |
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Authors: | V Marino I S de la Lande M Newlyn D A S Parker |
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Institution: | (1) Department of Dentistry, The University of Adelaide, G.P.O. Box 498, 5001 Adelaide, South Australia, Australia;(2) Department of Clinical and Experimental Pharmacology, The University of Adelaide, G.P.O. Box 498, 5001 Adelaide, South Australia, Australia |
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Abstract: | Summary The uptake and metabolism of 3H-noradrenaline has been examined in the FL cell-line derived originally from human amnion. Cell cultures metabolised 3H-noradrenaline (1.0 mol/l) to 3H-normetanephrine and, to a lesser extent, to metabolites (not distinguished) of the O-methylated deaminated fraction; primary deaminated metabolites were not detected.
3(H-normetanephrine formation a) was not saturable in the noradrenaline concentration range 0.2–150 mol/l, b was decreased to 20%–30% of control levels by uptake2 inhibitors (O-methylisoprenaline, 20 and 100 mol/l; cimetidine, 10 mol/l; hydrocortisone, 200 mol/l) and c, was almost insensitive to uptake1 inhibitors (cocaine, 30 mol/l; desipramine, 3 mol/l).Uptake of noradrenaline was manifested after 30 minutes as a 6-fold increase in the cell content of the amine following inhibition of catechol-O-methyl transferase, either alone or in conjunction with inhibition of monoamine oxidase. Uptake was decreased maximally to 40% of control levels by O-methylisoprenaline. IC50 values for inhibition of the O-methylisoprenaline-sensitive component of uptake were (in mol/l): corticosterone (0.3), papaverine (1.1), O-methylisoprenaline (3.0), cimetidine (6.0), (–)noradrenaline (460), and tetraethylammonium (2230). Except for the last agent, for which a comparative value is not available, the IC50's are in good agreement with those for inhibition of uptake2 in the Caki-1 cell-line reported by other investigators.The component of uptake resistant to O-methylisoprenaline was depressed by papaverine (a 50% decrease at 50 mol/l), but was not affected by the other uptake2 inhibitors or by cocaine (30 mol/l).It is concluded that the FL cell possesses an extraneuronal metabolising system very similar to the system in tissues such as heart and smooth muscle where transport of noradrenaline into the cell by uptake2 is followed by rapid O-methylation via catechol-O-methyl transferase. The only difference appears to be the absence of saturation of 3H-normetanephrine formation in the FL cell at low micromolar concentrations of 3H-noradrenaline. The presence of a second uptake process is suggested by the inhibitory effect of papaverine on uptake resistant to O-methylisoprenaline; lack of effect of cocaine implies that this second process is not uptake,.Abbreviations COMT
catechol-O-methyl transferase
- DOMA
dihydroxymandelic acid
- DOPEG
dihydroxyphenylethylene glycol
- MAO
monoamine oxidase
- NMN
normetanephrine
- OMDA
O-methylated and deaminated metabolite fraction
- OMI
3-O-methylisoprenaline
- TEA
tetraethylammonium
Correspondence to I. S. de la Lande at the above address |
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Keywords: | Human amnion FL cells Noradrenaline Uptake2 O-methylation Papaverine |
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