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Ca2+ mobilization in nontransformed ciliary nonpigmented epithelial cells
T Ohuchi1, N Yoshimura, H Tanihara
1Department of Ophthalmology, Kyoto University Faculty of Medicine, Japan.
Investigative Ophthalmology & Visual Science
|April 1, 1992
Summary
This study confirms that nonpigmented epithelial cells in humans and rabbits utilize a calcium signaling system. Different drugs trigger distinct calcium (Ca2+) responses in these cells, indicating varied cellular mechanisms.
Area of Science:
- Ophthalmology
- Cell Biology
- Physiology
Background:
- Nonpigmented epithelial (NPE) cells play a crucial role in ocular physiology.
- Understanding the calcium second messenger system in NPE cells is vital for elucidating cellular functions and responses to stimuli.
- Previous research has suggested the presence of signaling pathways in these cells, but detailed characterization of calcium dynamics was needed.
Purpose of the Study:
- To investigate the drug-dependent calcium (Ca2+) signaling system in cultured human and rabbit nonpigmented epithelial (NPE) cells.
- To characterize the cytosolic free Ca2+ concentration ([Ca2+]i) transients induced by various agonists.
- To determine species-specific differences and agonist-specific response patterns in NPE cells.
Main Methods:
- Cultured human and rabbit NPE cells were utilized.
- A fluorescent Ca2+ indicator, fura-2, was employed to measure cytosolic free Ca2+ concentration ([Ca2+]i).
- Digital video-imaging systems were used to record drug-induced [Ca2+]i transients.
Main Results:
- Basal [Ca2+]i levels were established for both human (141.9 ± 1.2 nM) and rabbit (157.0 ± 1.4 nM) NPE cells.
- Norepinephrine and epinephrine significantly increased [Ca2+]i in rabbit NPE cells but had minimal effect in human cells.
- Carbachol induced a significant [Ca2+]i increase in NPE cells from both species, with distinct monophasic (norepinephrine) and biphasic (carbachol) response patterns observed.
- Agonist-induced responses were blocked by specific antagonists (phentolamine for norepinephrine, atropine for carbachol).
- Extracellular calcium chelation shortened the duration of carbachol- and norepinephrine-induced responses.
Conclusions:
- The study confirms the presence and functional significance of the calcium signaling system in cultured human and rabbit NPE cells.
- NPE cells exhibit differential responses to adrenergic and cholinergic agonists, suggesting distinct receptor-mediated calcium mobilization pathways.
- These findings provide a foundation for understanding the role of calcium signaling in NPE cell function and potential therapeutic interventions.