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Naj Sharif, Julie Crider; Signal Transduction in Cultured Human Iridial Melanocytes and Fibroblasts. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2055.
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© ARVO (1962-2015); The Authors (2016-present)
Receptor-coupled signaling systems in human iridial fibroblasts (HIF) and human iridial melanocytes (HIM) were investigated to better understand their involvement in the iridial hyper-pigmentation observed during treatment of ocular hypertension with FP-class prostaglandin analogs.
[3H]-inositol phosphates ([3H]-IPs) generated were measured by ion-exchange chromatography and liquid scintillation spectroscopy. cAMP generated was quantified using an enzyme immunoassay.
HIF cells exhibited a robust phosphoinositide (PI) hydrolysis response to FP-class PG analogs: cloprostenol (potency, EC50 = 2.4 ± 0.5 nM, n = 5), fluprostenol (EC50 = 5.3 ± 0.6 nM, n = 3), PGF2α (EC50 = 54 ± 18 nM, n = 5), and latanoprost acid (EC50 = 121 ± 17 nM, n = 4). Other PGs exhibited the following potencies (EC50) fin the PI assays in HIF cells: PGD2 EC50 = 327 ± 195 nM; PGE2 EC50 = 550 ± 50 nM; and two TP-receptor agonists (I-BOP, EC50 = 23 ± 8 nM; U-46619 EC50 = 1.1 ± 0.4 µM; all n = 3). Endothelin-1 (ET-1) and histamine increased [3H]-IPs production in HIF and HIM cells. HIM cells exhibited minimal PI turnover response to cloprostenol, latanoprost acid, latanoprost, PGF2α, PGE2 and histamine, but there were robust responses to ET-1 (EC50 = 4.6 nM, n = 2) and an ETB-receptor agonist (BQ-3020, EC50 = 5 nM, n = 2) that were blocked by an ETB-antagonist (BQ-788, IC50 = 21 ± 6 nM, n = 3). In the adenylyl cyclase activation assay, numerous PGs (1 and 10 µM) stimulated cAMP production in HIF cells yielding the following rank order of efficacy: PGI2 > PGE2 > misoprostil > isoproterenol = BW245C > PGD2 = PGF2α = fluprostenol. In HIM cells, PGE2 (EC50 = 1.3 ± 0.3 nM) and isoproterenol ((β-agonist; EC50 = 89 ± 13 nM) potently and efficaciously stimulated cAMP production and ICI-118851 (β2-antagonist) attenuated the effects of isoproterenol. However, latanoprost acid, latanoprost, ET-1 and BW245C (DP-receptor agonist) were relatively less efficacious than isoproterenol and PGE2 in HIM cells at stimulating cAMP production.
These studies have shown that while HIF cells express FP prostaglandin and histamine receptors coupled to phospholipase C to produce [3H]-IPs, the HIM cells lack such functionally active FP-receptors. In contrast, HIF and HIM cells express functional ET-1 receptors coupled to [3H]-IPs production and both cell-types respond to PGE2, BW245C and isoproterenol by generating cAMP. It is concluded that human iridial fibroblasts and melanocytes respond differently to PGs and histamine, but in the same manner to ET-1, isoproterenol and BW245C. This may have relevance to the intercellular communication within the iris relative to the melanogenic processes.
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