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The force driving the extraneuronal transport mechanism for catecholamines (uptake2)
E Schömig1, J Babin-Ebell, H Russ
1Institut für Pharmakologie und Toxikologie, Universität Würzburg, Federal Republic of Germany.
Naunyn-Schmiedeberg'S Archives of Pharmacology
|April 1, 1992
Summary
Uptake2 transports protonated noradrenaline into cells. Membrane potential, influenced by cell depolarization, drives this uptake by affecting transport rates and accumulation.
Area of Science:
- Pharmacology
- Cell Biology
- Neuroscience
Background:
- Uptake2, a transporter system, has been identified in the Caki-1 cell line.
- Caki-1 cells possess a metabolizing system where catechol-O-methyl transferase (COMT) activity dominates over monoamine oxidase (MAO).
Purpose of the Study:
- To investigate the intracellular fate of 3H-noradrenaline following uptake2 translocation in Caki-1 cells.
- To analyze the driving force behind the uptake2 transport mechanism.
Main Methods:
- Enzyme inhibition of COMT and MAO.
- Measurement of initial uptake rates of 3H-noradrenaline across varying extracellular pH.
- Cell depolarization experiments using three distinct methods.
- Time-course analysis of 3H-noradrenaline and 3H-isoprenaline accumulation in Caki-1 cells and perfused rat heart, respectively.
Main Results:
- Uptake2 in Caki-1 cells transports the protonated form of 3H-noradrenaline.
- Cellular depolarization significantly inhibited inward transport.
- Depolarization reduced the rate constant for inward transport (kIN) and increased the rate constant for outward movement (kOUT).
- Depolarization led to a reduced steady-state accumulation factor.
Conclusions:
- The membrane potential is proposed as the primary driving force for uptake2.
- Experimental results, including altered transport rates and accumulation factors upon depolarization, support the role of membrane potential in uptake2.
- Uptake2's substrate specificity for protonated species is crucial for its function, modulated by membrane potential.
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