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RC Falcone, SJ Hubbs, JD Vanderloo, JC Prosser, J Little, B Gomes, D Aharony and RD Krell
Department of Pharmacology, Zeneca Pharmaceuticals Group, Business Unit of ZENECA Inc., Wilmington, Delaware.
Specific binding of [3H]bradykinin (BK) to guinea pig gall bladder (GPGB) membranes was protein dependent, rapid (Kon = 0.067 min-1) with high affinity (Kd = 0.45 +/- 0.02; n = 3), saturable (Bmax = 546 +/- 56 fmol/mg of protein) and showed no cooperativity (nH = 1.19 +/- 0.08). A BK B2 receptor type was indicated by the rank order of potency for inhibition of binding by B2 antagonists, [(D)Arg-[Hyp3,Thi5,(D)Tic7- Oic8]-bradykinin (HOE140) > (D)Arg-[Hyp3,(D)HypE(transpropyl)7-Oic8]- bradykinin (NPC17731) > (D)Arg-[Hyp3,Thi5, (D)Tic7-Tic8]-bradykinin (NPC16731) > (D)Arg-[Hyp3,(D)Phe7]-bradykinin (NPC567)] and agonists (BK = kallidin = Tyr(Me)8-BK > Tyr8-BK,> Hyp4-kallidin) as well as inactivity of the B1 agonist des(Arg9)-BK. Nonhydrolyzable GTP analogs (GTP-gamma-S and guanylyl-5'-imido-diphosphate) produced 80% inhibition of specific binding suggesting receptor coupling to guanine nucleotide- binding proteins. BK increased polyphosphoinositide hydrolysis in chopped GPGB in a concentration-dependent manner (0.01-300 microM; EC50 = 414 +/- 171 nM; n = 3-9 tissues/concentration). HOE140 and NPC16731, inhibited BK-induced polyphosphoinositide hydrolysis but only the latter appeared competitive (pKb 8.09 +/- 0.19, n = 3). U73122, an inhibitor of phospholipase C pathway, also inhibited BK-induced turnover in GPGB (IC50 = 46.9 +/- 17.3 nM). BK produced a concentration- related contraction of isolated strips of GPGB. Indomethacin significantly decreased both the potency and efficacy of BK whereas thiorphan, a neutral endopeptidase inhibitor, and/or captopril, an angiotensin-converting enzyme inhibitor, enhanced potency.(ABSTRACT TRUNCATED AT 250 WORDS)
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