GRP-preferring bombesin receptors increase generation of inositol phosphates and tension in rat myometrium

In the estrogen-treated rat myometrium, bombesin (Bn) and related agonists triggered contraction and the increased generation of inositol phosphates. The relative order of potencies was identical for both responses: Bn = gastrin releasing peptide (GRP) = litorin = neuromedin C >> neuromedin B. Two specific GRP-preferring receptor antagonists, namely [D-Phe6]Bn-(6-13) methyl ester and [Leu14,psi 13-14]Bn were inhibitory for both Bn-mediated tension and generation of inositol phosphates. [125I-Tyr4]Bn bound to myometrial membranes with high affinity (Kd = 104 pM) to a single class of sites in a saturable and reversible manner. The relative potencies for inhibiting binding were GRP = litorin = [Tyr4]Bn (Ki = 0.4 to 0.6 nM) >> neuromedin B (Ki = 10.3 nM). The high affinity displayed by [D-Phe6]Bn-(6-13) methyl ester (Ki = 2.8 nM) and [Leu14,psi 13-14]Bn (Ki = 35 nM) for competing for [Tyr4]Bn binding supported the involvement of a GRP-preferring Bn receptor. Guanine nucleotides decreased the binding of [125I-Tyr4]Bn and accelerated the rate of ligand dissociation, reflecting the coupling of receptors to guanine nucleotide regulatory proteins (G proteins). The results demonstrate that rat myometrium expresses functional GRP-preferring Bn receptors whose activation stimulates the phospholipase C pathway, pertussis toxin-insensitive event that contributes to Bn-mediated uterine contractions.

Download Full-text

Neuromedin B receptor in esophagus: evidence for subtypes of bombesin receptors

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1989.256.4.g747 ◽

1989 ◽

Vol 256 (4) ◽

pp. G747-G758 ◽

Cited By ~ 4

Author(s):

T. Von Schrenck ◽

P. Heinz-Erian ◽

T. Moran ◽

S. A. Mantey ◽

J. D. Gardner ◽

...

Keyword(s):

Muscularis Mucosae ◽

Pancreatic Acini ◽

Tissue Sections ◽

High Affinity ◽

Neuromedin B ◽

Specific Receptors ◽

Relative Potencies ◽

Single Binding Site ◽

Bombesin Receptors ◽

Stimulation Of

To identify receptors for bombesin-related peptides in the rat esophagus, we measured binding of 125I-Bolton-Hunter neuromedin B (125I-BH-neuromedin B) and 125I-[Tyr4]bombesin to tissue sections from the rat esophagus and compared the results with those for rat pancreas. Esophagus bound both tracers, whereas pancreas bound only 125I-[Tyr4]bombesin. In each tissue binding was saturable, dependent on pH, on time, and on temperature, reversible, and specific. Autoradiography demonstrated binding of both tracers only to the muscularis mucosae of the esophagus and binding of 125I-[Tyr4]bombesin diffusely over pancreatic acini. In the esophagus, the relative potencies for inhibition of binding of both tracers were as follows: neuromedin B greater than bombesin greater than GRP = neuromedin C; similar relative potencies were found for causing contraction of muscle strips from whole esophagus and from the isolated muscularis mucosae. In pancreas tissue sections and dispersed acini, the relative potencies for inhibition of binding of 125I-[Tyr4]bombesin were as follows: bombesin greater than GRP = neuromedin C much greater than neuromedin B. Similar relative potencies were found for stimulation of enzyme secretion from dispersed pancreatic acini. Computer analysis in both tissues demonstrated only a single binding site. The present study demonstrates that rat esophagus muscle possesses specific receptors for bombesin-related peptides. Furthermore, this study shows that the esophageal bombesin receptors represent a previously unidentified class of bombesin receptors in that they have a higher affinity for neuromedin B than for bombesin. In contrast, the pancreatic bombesin receptors have, like all other bombesin receptors described to date, a high affinity for bombesin, but low affinity for neuromedin B.

Download Full-text

Receptor for myo-inositol trisphosphate from the microsomal fraction of Vigna radiata

Biochemical Journal ◽

10.1042/bj3060631 ◽

1995 ◽

Vol 306 (3) ◽

pp. 631-636 ◽

Cited By ~ 17

Author(s):

S Biswas ◽

B Dalal ◽

M Sen ◽

B B Biswas

Keyword(s):

Molecular Mass ◽

Vigna Radiata ◽

Mung Bean ◽

Microsomal Fraction ◽

Inositol Phosphates ◽

Binding Activity ◽

Low Density ◽

Native Form ◽

Single Class ◽

High Affinity

The microsomal fraction from mung-bean (Vigna radiata) hypocotyl was found to contain Ins (1,4,5)P3- and Ins(2,4,5)P3-binding activity. Preincubation of the microsomal fraction with thiol-containing reagents reduced specific InsP3 binding. A single class of binding site with a Kd value of 1.5 nM and Bmax. of 1.1 pmol/mg of protein was detected. Other myo-inositol phosphates exhibited little affinity for this protein. The binding protein was purified to homogeneity and the molecular mass of the native form recorded as 400 kDa. However, under denaturing conditions the molecular mass was 110 kDa, suggesting that the protein is a homotetramer. That this protein is associated with Ca2+ release was confirmed by including it in proteoliposomes and adding Ins(1,4,5)P3 or Ins(2,4,5)P3. The affinity of Ins(1,4,5)P3 is 3-fold higher than that of Ins(2,4,5)P3. The binding affinity of InsP3 is also reflected in the extent of Ca2+ released from the microsomal fraction. Heparin inhibits binding of InsP3 to the protein, the K1/2 being 0.26 microM. It is also shown that the protein acts as a receptor for InsP3 with characteristics of high affinity and low density.

Download Full-text

Membrane reconstitution of high-affinity .alpha.2-adrenergic agonist binding with guanine nucleotide regulatory proteins

Biochemistry ◽

10.1021/bi00386a061 ◽

1987 ◽

Vol 26 (12) ◽

pp. 3664-3672 ◽

Cited By ~ 38

Author(s):

Marian H. Kim ◽

Richard R. Neubig

Keyword(s):

Regulatory Proteins ◽

Guanine Nucleotide ◽

Agonist Binding ◽

Adrenergic Agonist ◽

Membrane Reconstitution ◽

High Affinity ◽

Guanine Nucleotide Regulatory Proteins

Download Full-text

Contractile effect of bombesin on guinea pig lung in vitro: involvement of gastrin-releasing peptide-preferring receptors

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1993.264.1.l80 ◽

1993 ◽

Vol 264 (1) ◽

pp. L80-L86 ◽

Cited By ~ 3

Author(s):

E. Lach ◽

E. B. Haddad ◽

J. P. Gies

Keyword(s):

Methyl Ester ◽

Guinea Pig ◽

Binding Studies ◽

Gastrin Releasing Peptide ◽

Peripheral Airways ◽

Neuromedin B ◽

Specific Antagonist ◽

Acid Metabolites ◽

The Right

Bombesin (Bn) and related agonists produce a potent contractile response in guinea pig peripheral airways in vitro, with the following relative potencies: bombesin > gastrin-releasing peptide (GRP) > neuromedin C ≫ neuromedin B. Specific GRP-preferring receptor antagonists, namely [D-Phe6]Bn-(6–13)methyl ester and [D-Phe6,Cpa14,psi 13–14]Bn(6–14)-NH2, inhibited bombesin-induced lung contraction with high potencies [negative logarithm of the molar concentration of antagonist that produces a twofold shift to the right in the agonist dose-response curve (pA2) of 7.1 and 7.2, respectively], whereas the less-specific antagonist [Leu14,psi 13–14]Bn has a lower one (pA2 of 5.6). In binding studies, the high affinities of GRP, [D-Phe6]Bn(6–13)methyl ester and [D-Phe6,Cpa14,psi 13–14]Bn(6–14)NH2 in contrast with the low affinity of neuromedin B agree with the hypothesis that GRP-preferring receptors are involved in bombesin-induced bronchoconstriction. Bombesin-induced bronchoconstriction is unaffected by atropine, hexamethonium, propranolol, triprolidine, methysergide, Ro 19–3704, and indomethacin or AA-861, suggesting that the Bn response does not occur via a mechanism involving the corresponding endogeneous agents or via the release of arachidonic acid metabolites. Moreover, the effect of Bn is insensitive to capsaicin pretreatment, excluding the involvement of endogeneous neuropeptides. Present results provide evidence that Bn-induced bronchoconstriction results from a direct effect of Bn on bronchial smooth muscle GRP-preferring receptors.

Download Full-text