103.
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 (EC
50) 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-Arg
9-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;pA
2n=8.97–9.21,
n=3–4) and byD-Arg
0[Hyp
3,-Thi
5,8,-DPhe
7]-BK (molar potency=251 nM;-log potency, pK
b=6.6), two selective B
2-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 B
2-receptor subtype.
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