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Intracellular pathways regulating ciliary beating of rat brain ependymal cells
T Nguyen1, W C Chin, J A O'Brien
1Departments of Bioengineering, Physiology & Biophysics and Medicine, University of Washington, Box 357962, Seattle, Washington 98195, USA.
The Journal of Physiology
|February 17, 2001
Summary
Serotonin (5-HT) increases cilia beat frequency in brain ventricles via calcium signaling, while ATP decreases it through a cAMP-dependent pathway. These findings reveal neurotransmitter regulation of ependymal cell function in the central nervous system.
Area of Science:
- Neuroscience
- Cell Biology
- Neurophysiology
Background:
- Mammalian brain ventricles are lined by ciliated ependymal cells, crucial for cerebrospinal fluid (CSF) dynamics.
- Mechanisms by which neurotransmitters regulate cilia beat frequency (CBF) in these cells are largely unknown.
- Understanding neurotransmitter control of ependymal cells is vital for comprehending central nervous system (CNS) signaling and CSF flow.
Purpose of the Study:
- To investigate the effects of serotonin (5-HT) and adenosine triphosphate (ATP) on the cilia beat frequency (CBF) of mammalian brain ependymal cells.
- To elucidate the intracellular signaling pathways, including calcium (Ca2+) and cyclic adenosine monophosphate (cAMP), involved in mediating these responses.
- To determine if neurotransmitters act directly on ependymal cells to modulate CBF.
Main Methods:
- Cultured rat brainstem slices and acutely isolated ciliated ependymal cells were used to measure CBF.
- Neurotransmitters (5-HT, ATP) were applied, and their effects on CBF were quantified.
- Intracellular Ca2+ levels ([Ca2+]c) were measured using fluorescence microscopy.
- Experiments were conducted in Ca2+-free solutions, and forskolin and caged cAMP were used to probe cAMP-mediated pathways.
Main Results:
- Serotonin (5-HT) significantly increased CBF in a dose-dependent manner, mediated by a rise in intracellular Ca2+ involving IP3-sensitive stores and CRAC channels.
- ATP significantly decreased CBF, independent of extracellular Ca2+ and intracellular Ca2+ changes, suggesting a Ca2+-independent pathway.
- Forskolin and uncaged cAMP also decreased CBF, supporting a cAMP-mediated mechanism for ATP's effect.
- Responses observed in isolated cells mirrored those in brain slices, indicating direct neurotransmitter action on ependymal cells.
Conclusions:
- Neurotransmitters 5-HT and ATP exert opposing effects on mammalian brain ependymal cell CBF.
- 5-HT increases CBF via a Ca2+-dependent pathway, while ATP decreases CBF through a Ca2+-independent cAMP-mediated pathway.
- These findings highlight a novel mechanism for active CNS signaling involving direct neurotransmitter modulation of ependymal cell function and CSF dynamics.