Carbachol desensitizes pancreatic enzyme secretion by downregulation of receptors

1990 ◽  
Vol 258 (1) ◽  
pp. G107-G121 ◽  
Author(s):  
R. Vinayek ◽  
M. Murakami ◽  
C. M. Sharp ◽  
R. T. Jensen ◽  
J. D. Gardner
Keyword(s):  
Pancreatic Enzyme ◽  
Cholinergic Receptors ◽  
Single Class ◽  
Amylase Release ◽  
Pancreatic Acini ◽  
Cck Receptors ◽  
High Affinity ◽  
Kinase C ◽  
Pancreatic Enzyme Secretion ◽  
Bombesin Receptors

First incubating guinea pig pancreatic acini with carbachol reduced the subsequent stimulation of amylase release caused by carbachol, cholecystokinin octapeptide (CCK-8), and bombesin but not that caused by vasoactive intestinal peptide, substance P, 8-bromoadenosine 3',5'-cyclic monophosphate, A23187, or 12-O-tetradecanoylphorbol-13-acetate. Carbachol also reduced the subsequent binding of N-[3H]methylscopolamine, 125I-CCK-8, and 125I-[Tyr4]bombesin. Pancreatic acini possess a high-affinity class of cholinergic receptors and a low-affinity cholinergic receptors appears to produce the reduction in carbachol-stimulated amylase release and binding of N-[3H]methylscopolamine. First incubating acini with carbachol caused a complete loss of high-affinity cholinergic receptors with no change in the number or affinity of low-affinity cholinergic receptors. Carbachol occupation of low-affinity cholinergic receptors appears to produce the reduction in CCK-8- and bombesin-stimulated amylase release and in binding of 125I-CCK-8 and 125I-[Tyr4]bombesin. Acini possess two classes of CCK receptors. One class has a high affinity for CCK-8; the other class has a low affinity for CCK-8. First incubating acini with carbachol caused a 60% decrease in the number of high-affinity CCK receptors with no change in the number of low-affinity receptors or the affinities of either class of receptors for CCK-8. Acini possess a single class of bombesin receptors, and first incubating acini with carbachol caused a 40% decrease in the number of bombesin receptors with no change in their affinity for bombesin. 12-O-tetradecanoyl phorbol-13-acetate reproduced the action of carbachol on binding of N-[3H]methylscopolamine and 125I-CCK-8 but not on binding of 125I-[Tyr4]bombesin, suggesting that carbachol activation of protein kinase C may in some way mediate the effect of carbachol on receptors for carbachol and those for CCK but not that on receptors for bombesin.

Regulation of bombesin receptors on pancreatic acini by cholecystokinin

1989 ◽  
Vol 256 (2) ◽  
pp. G291-G298
Author(s):  
M. Younes ◽  
S. A. Wank ◽  
R. Vinayek ◽  
R. T. Jensen ◽  
J. D. Gardner
Keyword(s):  
Guinea Pig ◽  
Response Curve ◽  
Binding Capacity ◽  
The Other ◽  
Single Class ◽  
Pancreatic Acini ◽  
Cck Receptors ◽  
Cyclic Monophosphate ◽  
High Affinity ◽  
Bombesin Receptors

When guinea pig pancreatic acini are first incubated with the COOH-terminal octapeptide of cholecystokinin (CCK-8), washed, and then reincubated with 125I-[Tyr4]bombesin (125I-[Tyr4]BN) there is a significant decrease in binding of 125I-[Tyr4]BN compared with that observed with pancreatic acini that have been first incubated with no additions. The CCK-8-induced decrease in binding is maximal after 90 min of first incubation is abolished by reducing the temperature of the first incubation from 37 to 4 degrees C or by adding L364,718 to the first incubation and cannot be reproduced by first incubating acini with A23187, 8-bromoadenosine 3',5'-cyclic monophosphate (8Br-cAMP), 8-bromoadenosine 3',5'-cyclic monophosphate (8Br-cGMP), or 12-O-tetradecanoylphorbol 13-acetate. 125I-[Tyr4]BN interacts with a single class of receptors on pancreatic acini, and first incubating acini with CCK-8 decreases the affinity of BN receptors for BN with no change in the maximal binding capacity. CCK-8 does not alter the rate at which bound 125I-[Tyr4]BN dissociates from pancreatic acini; therefore, CCK-8 must alter the rate at which the radiolabeled BN analogue associates with its receptor. Pancreatic acini possess two classes of CCK receptors: one has a high affinity for CCK-8; the other has a low affinity for CCK-8. The dose-response curve for CCK-8-induced inhibition of binding of 125I-[Tyr4]BN appears to to reflect occupation of low-affinity CCK receptors by CCK-8.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbachol acts through protein kinase C to modulate cholecystokinin receptors on pancreatic acini

1991 ◽  
Vol 261 (6) ◽  
pp. G981-G986 ◽  
Author(s):  
D. S. Louie ◽  
O. Y. Chung
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Binding Capacity ◽  
Muscarinic Agonist ◽  
Amylase Release ◽  
Pancreatic Acini ◽  
Cck Receptors ◽  
High Affinity ◽  
Total Binding ◽  
Kinase C

Cholecystokinin (CCK) and cholinergic agonists are both major stimulants of pancreatic enzyme secretion and both utilize a common calcium-phosphoinositide-mediated receptor coupling system. In this study we investigated the modulation of pancreatic acinar CCK receptors by the muscarinic agonist carbachol (CCh) and investigated the intracellular mechanisms involved in the modulation. Acini were isolated from rat pancreas and dispersed in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-Ringer solution. Preincubation with 0.1 mM carbachol for 60 min reduced the CCK octapeptide (CCK-8; 100 pM)-stimulated amylase release by 43 +/- 5%. Binding of 125I-Bolton-Hunter-labeled CCK-8 (125I-BH-CCK-8) revealed two classes of CCK receptors, a high affinity with a dissociation constant (Kd) of 20 pM and a low affinity with a Kd of 2.3 nM. Pretreatment with 100 microM CCh decreased total binding by 35 +/- 6%, affecting the binding capacity of the high-affinity site, without change in the maximal binding capacity of the low-affinity site and no change in the Kd of either site. Preincubation of acini with 12-O-tetradecanoylphorbol 12,13-acetate (TPA, 1 microM), an activator of protein kinase C (PKC), decreased subsequent CCK-8-stimulated amylase release, and total binding of 125I-BH-CCK-8 to a similar extent as with pretreatment with CCh. The inhibitory effect of TPA or CCh on CCK-8-stimulated amylase release was reversed by simultaneous preincubation with H-7, an inhibitor of PKC. Pretreatment of acini with the calcium ionophore A23187, vasoactive intestinal peptide, or 8-bromoadenosine 3',5'-cyclic monophosphate had no effect on 125I-BH-CCK-8 binding. After CCh or TPA preincubation, CCK-8-stimulated production of [3H]inositol phosphates was inhibited by at least 49%.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor occupation, calcium mobilization, and amylase release in pancreatic acini: effect of CCK-JMV-180

1989 ◽  
Vol 257 (2) ◽  
pp. G202-G209 ◽  
Author(s):  
S. Sato ◽  
H. A. Stark ◽  
J. Martinez ◽  
M. A. Beaven ◽  
R. T. Jensen ◽  
...  
Keyword(s):  
Response Curve ◽  
Cytosolic Calcium ◽  
Calcium Mobilization ◽  
Amylase Release ◽  
Pancreatic Acini ◽  
Rat Pancreas ◽  
Cck Receptors ◽  
High Affinity ◽  
Low Concentrations ◽  
The Relationship

We examined the relationships between receptor occupation, calcium mobilization, and stimulated amylase release for cholecystokinin octapeptide (CCK-8) and for CCK-JMV-180, an analogue of the COOH-terminal heptapeptide of CCK having the structure Boc-Tyr(SO3)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester using dispersed acini from rat pancreas. CCK-8 and CCK-JMV-180 each bind to two classes of CCK receptors: one class has a high affinity for CCK-8 and CCK-JMV-180 and the other class has a low affinity for CCK-8 and CCK-JMV-180. Mobilization of cellular calcium was assessed by measuring cytosolic calcium with a fluorescent indicator and by measuring outflux of radioactive calcium from preloaded cells. In terms of causing an increase in cytosolic calcium or an increase in calcium outflux, CCK-JMV-180 was 50-60% as efficacious as CCK-8. Analysis of the relationship between receptor occupation and calcium mobilization caused by CCK-8 and CCK-JMV-180 in combination indicates that calcium mobilization is caused by occupation of low-affinity CCK receptors. Comparison of the dose-response curve for calcium mobilization and amylase release stimulated by CCK-8 or CCK-JMV-180 indicates that very low concentrations of each peptide stimulate amylase release without causing detectable calcium mobilization. At these very low concentrations, CCK-8 or CCK-JMV-180 do not cause potentiation of amylase release when combined with vasoactive intestinal peptide.

Pancreastatin inhibits pancreatic enzyme secretion by presynaptic modulation of acetylcholine release

1992 ◽  
Vol 262 (1) ◽  
pp. G113-G117 ◽  
Author(s):  
K. H. Herzig ◽  
D. S. Louie ◽  
K. Tatemoto ◽  
O. Y. Chung
Keyword(s):  
Acetylcholine Release ◽  
Pancreatic Enzyme ◽  
Exocrine Secretion ◽  
Enzyme Secretion ◽  
Neural Pathways ◽  
Amylase Release ◽  
Pancreatic Acini ◽  
Presynaptic Modulation ◽  
Pancreatic Enzyme Secretion ◽  
Pancreatic Fistulas

Pancreastatin (PST), a 49-amino acid polypeptide, inhibits endocrine and exocrine pancreatic functions. In this study, we examined the mechanism of the inhibitory action of PST on exocrine pancreatic secretion in the rat. In anesthetized rats prepared with pancreatic fistulas, intravenous administration of PST (500 pM.kg-1.h-1) completely inhibited 2-deoxyglucose (75 mg/kg)-stimulated amylase output to below basal levels. Because 2-deoxyglucose acts to stimulate the vagus, we assessed the ability of PST to inhibit carbachol-stimulated amylase release from isolated rat pancreatic acini. PST suppressed neither carbachol- nor cholecystokinin-stimulated amylase release, indicating that PST inhibits exocrine secretion via indirect mechanisms. To examine neural pathways for inhibition, we used pancreatic lobules to examine the action of PST on intrapancreatic neurons. Incubation of pancreatic lobules in 75 mM potassium buffer stimulated amylase release by a cholinergic pathway. PST dose dependently inhibited potassium-evoked amylase release, with maximal inhibition of 49.6 +/- 11%. In addition, when lobules were incubated with [3H]choline, PST inhibited KCl-stimulated release of synthesized [3H]acetylcholine by 43 +/- 5.7%. Other studies demonstrate that PST inhibits rat pancreatic enzyme secretion via presynaptic modulation of acetylcholine release.

Pancreatic polypeptide inhibits pancreatic enzyme secretion via a cholinergic pathway

1987 ◽  
Vol 253 (5) ◽  
pp. G706-G710 ◽  
Author(s):  
G. Jung ◽  
D. S. Louie ◽  
C. Owyang
Keyword(s):  
Pancreatic Polypeptide ◽  
Acetylcholine Release ◽  
Pancreatic Enzyme ◽  
Enzyme Secretion ◽  
Dependent Manner ◽  
Amylase Release ◽  
Opioid Receptor Antagonists ◽  
Cholinergic Pathway ◽  
Pancreatic Enzyme Secretion ◽  
Dose Dependent

In rat pancreatic slices, rat pancreatic polypeptide (PP) or C-terminal hexapeptide of PP [PP-(31-36)] inhibited potassium-stimulated amylase release in a dose-dependent manner. The inhibition was unaffected by addition of hexamethonium but blocked by atropine. In contrast, PP(31-36) did not have any effect on acetylcholine- or cholecystokinin octapeptide-stimulated amylase release. In addition, when pancreatic slices were incubated with [3H] choline, PP(31-36) inhibited the potassium-evoked release of synthesized [3H] acetylcholine in a dose-dependent manner. The inhibitory action of PP was unaffected by adrenergic, dopaminergic, or opioid receptor antagonists. Thus PP inhibits pancreatic enzyme secretion via presynaptic modulation of acetylcholine release. This newly identified pathway provides a novel mechanism for hormonal inhibition of pancreatic enzyme secretion via modulation of the classic neurotransmitter function.

Carbachol-induced down-regulation of high-affinity receptors for vasoactive intestinal peptide

1989 ◽  
Vol 257 (3) ◽  
pp. G402-G408
Author(s):  
M. Murakami ◽  
R. Vinayek ◽  
R. T. Jensen ◽  
J. D. Gardner
Keyword(s):  
Vasoactive Intestinal Peptide ◽  
Response Curve ◽  
Cholinergic Receptors ◽  
The Other ◽  
Tetraacetic Acid ◽  
Muscarinic Cholinergic Receptors ◽  
Pancreatic Acini ◽  
Vip Receptors ◽  
High Affinity ◽  
Muscarinic Cholinergic

When dispersed acini from guinea pig pancreas are first incubated with carbachol, the subsequent binding of 125I-vasoactive intestinal peptide (VIP) is inhibited during a second incubation. This inhibitory action of carbachol on binding of 125I-VIP depends on time, temperature, and the concentration of carbachol in the first incubation and can be blocked by atropine. First incubating acini with A23187, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), cholecystokinin octapeptide, bombesin, or 12-O-tetradecanoylphorbol-13-acetate does not alter binding of 125I-VIP. Adding EGTA to the first incubation medium abolishes the effect of carbachol on binding of 125I-VIP. In control acini or acini first incubated with carbachol, approximately half of the bound 125I-VIP can be stripped by acetic acid. 125I-VIP interacts with two distinct classes of receptors on pancreatic acini. One has a high affinity for VIP (Kd, 1 nM); the other has a low affinity for VIP (Kd, 2 microM). First incubating acini with carbachol decreases the number but not the affinity of high-affinity VIP receptors with no change in the number or affinity of low-affinity VIP receptors. Pancreatic acini possess two classes of muscarinic cholinergic receptors: one has a high affinity (Kd, 4 microM) and the other has a low affinity (Kd, 698 microM) for carbachol. The dose-response curve for carbachol-induced inhibition of binding of 125I-VIP and that for occupation of low-affinity muscarinic cholinergic receptors by carbachol are similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Bovine pancreatic polypeptide as an antagonist of muscarinic cholinergic receptors

1987 ◽  
Vol 252 (3) ◽  
pp. G384-G391
Author(s):  
G. Z. Pan ◽  
L. Lu ◽  
J. M. Qian ◽  
B. G. Xue
Keyword(s):  
Pancreatic Polypeptide ◽  
Pancreatic Enzyme ◽  
Cholinergic Receptors ◽  
Enzyme Secretion ◽  
Amylase Secretion ◽  
Enzyme Release ◽  
Muscarinic Cholinergic Receptors ◽  
Bovine Pancreatic Polypeptide ◽  
Pancreatic Enzyme Secretion ◽  
Muscarinic Cholinergic

In dispersed acini from rat pancreas, it was found that bovine pancreatic polypeptide (BPP) and its C-fragment hexapeptide amide (PP-6), at concentrations of 0.1 and 30 microM, respectively, could significantly inhibit amylase secretion stimulated by carbachol (P less than 0.01 or 0.05, respectively), and this inhibition by BPP was dose dependent. 45Ca outflux induced by carbachol was also inhibited by BPP or PP-6, but they had no effect on cholecystokinin octapeptide- (CCK-8) or A23187-stimulated 45Ca outflux. BPP was also capable of displacing the specific binding of [3H]quinuclidinyl benzilate to its receptors, and it possessed a higher affinity (ki 35 nM) than carbachol (Ki 1.8 microM) in binding with M-receptors. It is concluded from this study that BPP acts as an antagonist of muscarinic cholinergic receptors in rat pancreatic acini. In addition, BPP inhibited the potentiation of amylase secretion caused by the combination of carbachol plus secretin or vasoactive intestinal peptide. This may be a possible explanation of the inhibitory effect of BPP on secretin-induced pancreatic enzyme secretion shown in vivo, since pancreatic enzyme secretion stimulated by secretin under experimental conditions may be the result of potentiation of enzyme release produced by the peptide in combination with a cholinergic stimulant.

A new CCK analogue differentiates two functionally distinct CCK receptors in rat and mouse pancreatic acini

1989 ◽  
Vol 257 (4) ◽  
pp. G594-G600 ◽  
Author(s):  
T. Matozaki ◽  
J. Martinez ◽  
J. A. Williams
Keyword(s):  
Competitive Inhibition ◽  
Inhibitory Effect ◽  
Leucine Incorporation ◽  
Amylase Release ◽  
Pancreatic Acini ◽  
Cck Receptors ◽  
Partial Agonists ◽  
Low Concentrations ◽  
Phenylalanine Residue ◽  
Stimulation Of

Analysis of the competitive inhibition of 125I-labeled cholecystokinin octapeptide (CCK-8) binding to isolated rat or mouse pancreatic acini showed that in both species CCK-8 interacts with two different affinity sites. A newly synthesized CCK analogue modified at the COOH-terminal phenylalanine residue totally inhibited 125I-CCK binding. This interaction occurred with sites of a single affinity in rat acini but with two different affinity sites in mouse acini. When acini were incubated with increasing concentrations of CCK-8, a biphasic stimulation of amylase release was observed. By use of rat acini, the analogs stimulated amylase release but caused no inhibition at supramaximal concentrations. By contrast, in mouse pancreatic acini, analogues showed a biphasic stimulation of amylase release similar to CCK-8. Both CCK-8 and the analogue stimulated [3H]leucine incorporation into protein at low concentrations in rat pancreatic acini. Higher concentrations of CCK-8 profoundly inhibited [3H]leucine incorporation, whereas the analogue had no inhibitory effect. Moreover, the analogue at higher concentrations blocked the inhibition of [3H]leucine incorporation caused by CCK-8 but did not affect carbamylcholine-induced inhibition. In mouse acini, however, the CCK analogue inhibited [3H]leucine incorporation similar to the effect of CCK-8. The results support the concept that occupancy of distinct affinity sites or states of the CCK receptor is associated with specific biological actions. A model of the CCK receptor is proposed in which two interchangeable affinity states exist. By occupying all the receptors in only one state, the new CCK analogues serve as partial agonists of some and antagonists of other actions of CCK.

Cholecystokinin (CCK)-induced desensitization of pancreatic enzyme secretion is mediated by low affinity CCK receptors

Peptides ◽  
1989 ◽  
Vol 10 (2) ◽  
pp. 337-341 ◽  
Author(s):  
D. Menozzi ◽  
H.A. Stark ◽  
J. Martinez ◽  
R.T. Jensen ◽  
J.D. Gardner
Keyword(s):  
Pancreatic Enzyme ◽  
Enzyme Secretion ◽  
Cck Receptors ◽  
Pancreatic Enzyme Secretion
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