Pharmacological Characterization of Bradykinin Receptors Coupled to Phosphoinositide Turnover in SV40-Immortalized Human Trabecular Meshwork Cells |
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Authors: | NA SHARIF SX XU |
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Institution: | Molecular Pharmacology Unit, Alcon Laboratories, Inc. (R2–19), 6201 South Freeway, Fort Worth, TX, 76134, U.S.A. |
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Abstract: | This study sought to pharmacologically characterize bradykinin receptors on SV40-immortalized human trabecular meshwork (HTM3) cells. Phosphoinositide (PI) turnover studies were conducted using 3H]myo-inositol-labeled HTM3 cells and anion exchange chromatography to quantify 3H]inositol phosphates generated in response to bradykinin (BK) and various BK analogs. The blockade of these responses was studied using two potent and receptor-subtype selective antagonists. BK and T-kinin (Ile-Ser-BK; TK) induced a 4.2–4.4 fold stimulation of PI turnover above base levels at 1–10 μM. Several other peptides unrelated to BK, including angiotensin II, endothelin, cholecystokinin, bombesin and peptide YY tested at 1–10 μMwere essentially inactive. The molar potencies (EC50) of BK, TK and close analogs were: BK=4.5±0.5 nM(n=6), Lys-BK=6.5±0.7 nM(n=3), TK=38.8±6.6 nM(n=8), Met-Lys-BK=41.5±13.4 nM(n=4), Des-Arg9-BK=2093±626 nM(n=4). All the latter BK-related peptides>were full agonists. The actions of BK and TK were potently and competitively antagonized by Hoe-140 (molar potency=0.6–1 nM;pA2n=8.97–9.21,n=3–4) and byD-Arg0Hyp3,-Thi5,8,-DPhe7]-BK (molar potency=251 nM;-log potency, pKb=6.6), two selective B2-type BK antagonists. In conclusion, rank order of potency of BK agonists and the blockade of BK- and TK-induced PI turnover by the selective antagonists are consistent with the classification of the BK receptors on HTM3 cells as the B2-receptor subtype. |
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Keywords: | bradykinin T-kinin trabecular meshwork cells phosphoinositide turnover inositol phosphates Hoe-140 outflow |
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