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Serotonin-storing secretory granules from thyroid parafollicular cells
J M Barasch1, H Tamir, E A Nunez
1Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York, NY 10032.
Summary
Sheep thyroid parafollicular cells store serotonin (5-HT) in granules containing a specific binding protein. These granules may be analogous to synaptic vesicles in serotonergic neurons.
Area of Science:
- Neuroscience
- Cell Biology
- Endocrinology
Background:
- Sheep thyroid parafollicular cells, derived from neural crest, serve as a model for studying serotonergic systems.
- Understanding the subcellular storage mechanisms of serotonin (5-HT) is crucial for neurobiology.
Purpose of the Study:
- To investigate the subcellular localization and storage of serotonin (5-HT) in sheep thyroid parafollicular cells.
- To characterize the 5-HT binding protein (SBP) and its role in granular storage within these cells.
Main Methods:
- Light and electron microscopic immunocytochemistry for 5-HT, 45/56 kDa SBP, and calcitonin.
- Granule isolation using metrizamide and Percoll density gradients.
- Affinity chromatography for cell purification, immunoblots, and 3H-5-HT uptake studies.
Main Results:
- Parafollicular cells contain calcitonin, 5-HT, and 45 kDa SBP, but not 56 kDa SBP.
- Secretory granules immunoreactive for calcitonin, 5-HT, and 45 kDa SBP were identified and isolated.
- Isolated granules demonstrated specific, reserpine-sensitive uptake of 3H-5-HT and lacked significant ATP stores.
Conclusions:
- Sheep parafollicular cell granules store serotonin (5-HT) via a mechanism distinct from ATP-dependent amine storage vesicles.
- The presence of 45 kDa SBP suggests functional analogy between these granular vesicles and synaptic vesicles of serotonergic neurons.