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John Cuppoletti, Danuta H. Malinowska, Kirti P. Tewari, Jayati Chakrabarti, Ryuji Ueno; Unoprostone Isopropyl and Metabolite M1 Activate BK Channels and Prevent ET-1–Induced [Ca2+]i Increases in Human Trabecular Meshwork and Smooth Muscle. Invest. Ophthalmol. Vis. Sci. 2012;53(9):5178-5189. doi: https://doi.org/10.1167/iovs.11-9046.
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Effects of cis-unoprostone isopropyl, its primary metabolite M1, trans-unoprostone isopropyl, latanoprost free acid, andfluprostenol were studied on Ca2+-activated K+ (BK) channels, plasma membrane potential, [cAMP]i, [cGMP]i, and steady state [Ca2+]i, and protection against endothelin-1 (ET-1)–induced steady state [Ca2+]i increases in human cortical neuronal (HCN-1A), trabecular meshwork (HTMC), and pulmonary artery smooth muscle (PASMC) cells. Effects on recombinant human prostaglandin (PG) receptors were determined.
BK channel currents were measured using whole-cell patch clamp; [cAMP]i, [cGMP]i with ELISAs; [Ca2+]i with indo-1; plasma membrane potential using diBAC4(3); and PG receptor effects with PG receptor-expressing cells and FLIPR fluo-4 Ca2+ assays.
Unoprostone isopropyl and M1 activated sustained iberiotoxin (IbTX)-sensitive, AL-8810 (FP receptor antagonist)-insensitive BK channel currents with EC50s of 0.51 ± 0.03 nM (n = 5) and 0.52 ± 0.03 nM (n = 6) in HTMCs; 0.61 ± 0.06 nM (n = 8) and 0.46 ± 0.04 nM (n = 5) for M1 in HCN-1A cells and PASMC, respectively. They caused AL-8810–insensitive, IbTX-sensitive membrane hyperpolarization at 10 nM; up to 100 nM had no effect on or decreased [cAMP]i, [cGMP]i, and [Ca2+]i; and prevented ET-1–induced [Ca2+]i increases. In contrast, 10 nM latanoprost free acid and fluprostenol caused membrane depolarization; increased [cAMP]i, [cGMP]i, and [Ca2+]i; and did not prevent ET-1–induced [Ca2+]i increases. Trans-unoprostone isopropyl had no effects. Unoprostone isopropyl (1.25 μM) had no effect on PG receptors, and neither did M1, except for activating the FP receptor with EC50 = 557.9 ± 55.2 nM (n = 4).
Prostones, unoprostone isopropyl and M1, are potent AL-8810–insensitive, stereospecific BK channel activators, without [cAMP]i, [cGMP]i, or [Ca2+]i involvement, and prevent ET-1–induced steady state Ca2+ increases in HTMCs.
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