Search PubMed⌕ Search

Biomedical subjects

T B Chen

Publications and source records attributed to T B Chen.

62 records · Page 4Linked to original sources
PubMed1986

Characterization of the binding of [3H]-(+/-)-L-364,718: a new potent, nonpeptide cholecystokinin antagonist radioligand selective for peripheral receptors.

[3H]-(+/-)-L-364,718 a new, potent and selective nonpeptide peripheral cholecystokinin (CCK) antagonist bound saturably and reversibly to rat pancreatic membranes. The radioligand recognized a single class of binding sites with a high affinity (Kd = 0.23 nM). The binding of [3H]-(+/-)-L-364,718 was stereospecific in that the more biologically active (-)-enantiomer demonstrated greater potency than the (+)-enantiomer. The rank order of potency of various CCK agonists and antagonists in displacing [3H]-(+/-)-L-364,718 correlated with their ability to displace [125I]CCK-8 and their known pharmacological activities in peripheral tissues. However, the absolute potencies of agonists were greater in displacing [125I]CCK-8 than [3H]-(+/-)-L-364,718. As described for other physiologically relevant receptor systems, the potency for displacement of [3H]-(+/-)-L-364,718 binding by CCK agonists, but not antagonists, was reduced by guanosine 5'-(beta, gamma-imido)triphosphate and NaCl and enhanced by MgCl2. [3H]-(+/-)-L-364,718 also demonstrated specific binding to bovine gall bladder tissue but not guinea pig brain or gastric glands, consistent with its selectivity as a peripheral CCK antagonist. [3H]-(+/-)-L-364,718 binding to pancreatic membranes was not affected by various pharmacological agents known to interact with other common peptide and nonpeptide receptor systems. These data indicate that [3H]-(+/-)-L-364,718 represents a new potent nonpeptide antagonist radioligand for the study of peripheral CCK receptors which may allow differentiation of agonist and antagonist interactions.

Animals↗
PubMed1985

Neuropeptide Y (NPY) binding sites in rat brain labeled with 125I-Bolton-Hunter NPY: comparative potencies of various polypeptides on brain NPY binding and biological responses in the rat vas deferens.

The binding of biologically active 125I-Bolton-Hunter (BH)-NPY to rat brain membranes was saturable and reversible and regulated by inorganic cations and guanyl nucleotides consistent with other neurotransmitter receptor systems. The concentration of specific 125I-NPY binding differed in various brain regions, being highest in the hippocampus and lowest in the cerebellum. Scatchard analysis of 125I-NPY binding showed a single class of receptor sites with a Kd = 0.1 nM and Bmax of 3 pmole/g tissue in hippocampus. Peptide YY, porcine and human NPY inhibited the specific 125I-BH-NPY binding with IC50 values of 50-120 pM. In contrast, human NPY free acid and pancreatic polypeptides from human (HPP), rat (RPP) and avian (APP) sources were much weaker (IC50 greater than or equal to 300 nM). The rank order of potencies for NPY analogs and the inactivity of APP and HPP fragment (31-36) on brain binding appeared to correlate with their relative activities in inhibiting contractions of the field-stimulated rat vas deferens. However, PYY, HPP and RPP exhibited activity in the field-stimulated rat vas deferens indicative of a possible action upon sites distinct from the brain NPY binding site.

Animals↗
PubMed1985

Cholecystokinin receptor mediated hydrolysis of inositol phospholipids in guinea pig gastric glands.

CCK-octapeptide (CCK-8) (EC50 = 0.5 nM), in the presence of Li+, increased 3H-inositol phosphate (IP) accumulation in guinea pig gastric glands prelabeled with 3H-inositol. CCK-8 desulfate, human gastrin I and pentagastrin were much less potent than CCK-8. Antagonists of CCK receptors such as proglumide, dibutyryl-c-GMP and CBZ-Tyr (SO3H)-Met-Gly-Trp-Met-AspNH2 shifted the CCK dose response curve to the right. However, histamine (H1 and H2), cholinergic, substance P and alpha- and beta-adrenergic receptor antagonists had no effect on 3H-IP accumulation induced by CCK. The results suggest that CCK receptor activation in gastric glands leads to an enhanced breakdown of inositol phospholipids which may relate to calcium mobilization and pepsinogen secretion.

Animals↗
PubMed1984

Further evidence that substance P partly mediates the action of cholecystokinin octapeptide (CCK-8) on the guinea pig ileum but not gall bladder: studies with a substance P antagonist.

The substance P antagonist, [D-Pro4-D- Trp7 ,9,10]substance P4-11, caused a pig parallel shift to the right of the cholecystokinin (CCK-8) dose-response curve in guinea pig ileum longitudinal muscle without changing the maximal contraction. The shift of the CCK-8 dose response was markedly reduced after desensitization of the tissues to substance P (SP). The SP antagonist had no effect upon CCK-8 responses of the guinea pig gall bladder, [125I]CCK pancreatic binding or contractions of the guinea pig ileum produced by acetylcholine or electrical stimulation. The data provide additional evidence for the involvement of SP in the action of CCK-8 on the guinea pig ileum but not the gall bladder.

Animals↗
PubMed1983

Increase in brain 125I-cholecystokinin (CCK) receptor binding following chronic haloperidol treatment, intracisternal 6-hydroxydopamine or ventral tegmental lesions.

Specific 125I-CCK receptor binding was significantly increased in brain tissue taken from guinea pig or mouse following chronic (2-3 week) daily administration of haloperidol (2-3 mg/kg/day). Scatchard analysis indicated the increase in CCK binding was due to an increased receptor number (B max) with no change in affinity (Kd). In guinea pigs, the increased CCK binding was observed in the mesolimbic regions and frontal cortex, but not in striatum, hippocampus nor posterior cortex. In mice, however, the increases occurred in both pooled cerebral cortical-hippocampal tissue, and in the remainder of the brain. Enhanced CCK receptor binding was also observed in membranes prepared from whole brain of mice one month following intracisternal injection of 6-hydroxydopamine. Additionally, an increase in CCK binding was observed in mesolimbic regions and frontal cortex, but not striatum or hippocampus, of guinea pigs 3 weeks after an unilateral radiofrequency lesions of the ipsilateral ventral tegmentum. The present studies demonstrate that three different procedures which reduce dopaminergic function in the brain enhance CCK receptor binding. The data provide further support for a functional interrelationship between dopaminergic systems and CCK in some brain regions and raise the possibility that CCK may play a role in the antipsychotic action of neuroleptics.

Animals↗
PubMedDate not supplied

RUBIDIUM, a program for computer-aided assignment of two-dimensional NMR spectra of polypeptides.

Taking advantage of the rule-based expert system technology, a program named RUBIDIUM (Rule-Based Identification In 2D NMR Spectrum) was developed to accomplish the automatic 1H NMR resonance assignments of polypeptides. Besides noise elimination and peak selection capabilities, RUBIDIUM detects the cross-peak patterns of amino acid residues in the COSY spectrum, assigning these patterns to amino acid types, performing sequential assignments using combined COSY/NOESY spectra, and finally, achieving the total assignment of the 1H NMR spectrum.

Amino Acid Sequence↗