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S Matsumoto, T Yorio, L DeSantis, I H Pang; Muscarinic effects on cellular functions in cultured human ciliary muscle cells.. Invest. Ophthalmol. Vis. Sci. 1994;35(10):3732-3738.
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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 microM, 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 pKi = 9.12, nonselective for muscarinic receptor subtypes), pirenzepine (pKi = 6.76, selective for the M1 receptor subtype), 4DAMP (pKi = 9.25, selective for the M1 and M3 subtypes), and fHHSiD (pKi = 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 microM. 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.
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