Abstract
Purpose. To characterize the pharmacology of the carbachol-induced changes of phospholipase C (PLC) activity and intracellular calcium concentration ([Ca2+](i)) in cultured human ciliary muscle cells. Methods. Changes in PLC activity of cultured human ciliary muscle cells were determined by production of inositol phosphates. Single-cell dynamic fluorescence ratio imaging was used to determine [Ca2+](i). Results. Carbachol, oxotremorine-M, aceclidine, and pilocarpine stimulated PLC with mean EC50s of 20, 8, 17, and 2 μM, respectively. The effect of carbachol on PLC was partially suppressed by extracellular Ca2+ depletion. This muscarinic effect was blocked by muscarinic antagonists, such as atropine (apparent pK(i) = 9.12, nonselective for muscarinic receptor subtypes), pirenzepine (pK(i) = 6.76, selective for the M1 receptor subtype), 4DAMP (pK(i) = 9.25, selective for the M1 and M3 subtypes), and fHHSiD (pK(i) = 7.77, selective for the M3 subtype). In [Ca2+](i) experiments, carbachol increased [Ca2+](i) transients in human ciliary muscle cells in a dose-dependent manner with a mean EC50 of 7 μM. 4DAMP was approximately 100 times more potent than pirenzepine in the inhibition of the carbachol-induced [Ca2+](i) increase. [Ca2+](i) oscillations were observed after carbachol stimulation and persisted after extracellular Ca2+ depletion. Conclusions. Muscarinic agonists activate PLC and increase [Ca2+](i) in cultured human ciliary muscle cells through an M3-like muscarinic receptor subtype.
Original language | English |
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Pages (from-to) | 3732-3738 |
Number of pages | 7 |
Journal | Investigative Ophthalmology and Visual Science |
Volume | 35 |
Issue number | 10 |
State | Published - 1994 |
Keywords
- M- muscarinic receptor subtype
- human ciliary muscle cell
- intracellular calcium
- muscarinic agonist
- phospholipase C