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Serotonin uptake by isolated adipose capillary endothelium
The Journal of Pharmacology and Experimental Therapeutics
|January 1, 1981
Summary
Rat endothelial cells actively transport serotonin (5-hydroxytryptamine, 5-HT) via a carrier-mediated mechanism at low concentrations. At higher concentrations, nonfacilitative diffusion becomes the primary uptake pathway.
Area of Science:
- Endocrinology
- Vascular Biology
- Neuroscience
Background:
- Endothelial cells play a crucial role in regulating vascular tone and function.
- Serotonin (5-hydroxytryptamine, 5-HT) is a key neurotransmitter and vasoactive substance.
- Understanding 5-HT uptake in microvessels is vital for comprehending its physiological effects.
Purpose of the Study:
- To investigate the mechanism of serotonin (5-HT) uptake by endothelial cells in rat microvessels.
- To characterize the kinetic parameters of 5-HT transport.
- To identify factors influencing 5-HT uptake in this specific vascular bed.
Main Methods:
- Isolation of capillary and microvessel endothelium from rat epididymal fat pads.
- Incubation of endothelial cells with radiolabeled [3H]-5-HT.
- Measurement of 5-HT uptake and determination of kinetic parameters (Km, Vmax).
- Assessment of inhibition by metabolic inhibitors, temperature changes, and specific antagonists.
Main Results:
- Endothelial cells demonstrated significant uptake of [3H]-5-HT.
- Kinetic analysis revealed an apparent Km of 3 x 10(-7) M and Vmax of 20 pmol/mg protein.
- Uptake was inhibited by ouabain, metabolic inhibitors, low temperature, and 5-HT antagonists (fluoxetine, imipramine).
- At 5-HT concentrations above Km, uptake shifted towards nonfacilitative diffusion.
Conclusions:
- Rat microvessel endothelial cells possess a high-affinity, carrier-mediated system for serotonin (5-HT) uptake.
- This transport system is energy-dependent and sensitive to specific inhibitors.
- At supra-saturating concentrations, passive diffusion contributes significantly to 5-HT uptake by these cells.