Dual pathways of internalization of the cholecystokinin receptor

Receptor molecules play a major role in the desensitization of agonist-stimulated cellular responses. For G protein-coupled receptors, rapid desensitization occurs via receptor phosphorylation, sequestration, and internalization, yet the cellular compartments in which these events occur and their interrelationships are unclear. In this work, we focus on the cholecystokinin (CCK) receptor, which has been well characterized with respect to phosphorylation. We have used novel fluorescent and electron-dense CCK receptor ligands and an antibody to probe receptor localization in a CCK receptor-bearing CHO cell line. In the unstimulated state, receptors were diffusely distributed over the plasmalemma. Agonist occupation stimulated endocytosis via both clathrin-dependent and independent pathways. The former was predominant, leading to endosomal and lysosomal compartments, as well as recycling to the plasmalemma. The clathrin-independent processes led to a smooth vesicular compartment adjacent to the plasmalemma resembling caveolae, which did not transport ligand deeper within the cell. Potassium depletion largely eliminated clathrin-dependent endocytosis, while not interfering with agonist-stimulated receptor movement into subplasmalemmal smooth vesicle compartments. These cellular endocytic events can be related to the established cycle of CCK receptor phosphorylation and dephosphorylation, which we have previously described (Klueppelberg, U. G., L. K. Gates, F. S. Gorelick, and L. J. Miller. 1991. J. Biol. Chem. 266:2403-2408; Lutz, M. P., D. I. Pinon, L. K. Gates, S. Shenolikar, and L. J. Miller. 1993. J. Biol. Chem. 268:12136-12142). The rapid onset and peak of receptor phosphorylation after agonist occupation correlates best with a plasmalemmal localization, while stimulated receptor phosphatase activity correlates best with receptor residence in intracellular compartments. We postulate that the smooth vesicular compartment adjacent to the plasmalemma functions for the rapid resensitization of the receptor, while the classical clathrin-mediated endocytotic pathway is key for receptor downregulation via lysosomal degradation, as well as less rapid resensitization.

Phosphopeptide mapping of cholecystokinin receptors on agonist-stimulated native pancreatic acinar cells

The cholecystokinin (CCK) receptor on the rat pancreatic acinar cell is a G protein-coupled receptor that is phosphorylated in response to homologous and heterologous agonist stimulation. In this work we have studied the stoichiometry of receptor phosphorylation and have utilized one-dimensional phosphopeptide mapping after cyanogen bromide cleavage to demonstrate that the third intracellular loop is the predominant domain of phosphorylation of this receptor in response to these treatments. Of the average 5 mol of phosphate/mol of receptor, greater than 95% was on the third loop, with the remainder residing on the carboxyl-terminal tail. Serine residues were the site of greater than 95% of phosphorylation, with threonine representing the remainder, and no phosphotyrosine was detected. Further, we have utilized two-dimensional phosphopeptide mapping after subtilisin cleavage to identify differing sites of CCK receptor phosphorylation which are dependent on the agonist utilized to stimulate this cell. Both qualitative and quantitative differences in phosphorylation sites were observed after acinar cell stimulation with different protein kinase C agonists. Further, distinct phosphopeptides on the map were identified as representing substrate(s) of a staurosporine-insensitive kinase activity stimulated only by receptor occupation with native CCK and were felt to represent site(s) of action of a member of the G protein-coupled receptor kinase family. This represents a sensitive and powerful approach that is applicable to sparse receptors residing in their native cellular environment to assess possible differences in patterns of phosphorylation which may be important in agonist-specific receptor regulation.

CCK-A receptor selective antagonists derived from the CCK-A receptor selective tetrapeptide agonist Boc-Trp-Lys(Tac)-Asp-MePhe-NH2 (A-71623)

Analogs of the CCK-A receptor selective agonist Boc-Trp-Lys(Tac)-Asp-MePhe-NH2 (A-71623) were prepared in which the lysine residue was replaced with L-4-aminophenylalanine and D-or L-3-aminophenylalanine. These new analogs were moderately potent antagonists of CCK-8 in the isolated guinea pig gallbladder with exceptional CCK-A receptor selectivity as evaluated in membrane preparations from CHO K1 cells stably transfected with human CCK-A and CCK-B receptors.

Performance of Israeli versus U.S. preschool children on the Miller Assessment for Preschoolers

OBJECTIVES

The Miller Assessment for Preschoolers (MAP) is a scale that can be used to evaluate preschool children with suspected preacademic problems. Before implementing the MAP in Israel, it was necessary to determine whether the U.S. norms were applicable to the Israeli preschool population.

METHOD

In a pilot study carried out in Israel, the Hebrew version of the MAP was administered to 2 age groups of 30 children each. The scores of Israeli children were compared with the U.S. norms on each of the MAP's 27 subtests, the five performance indices, and the total score.

RESULTS

There were no significant differences between the Israeli sample and the U.S. standardization sample in either age group on the MAP total score; significant differences were found in both age groups on the Foundations Index and on some specific subtests. Israeli children performed below U.S. norms on the Foundations Index.

CONCLUSION

These findings indicate that the performance of Israeli children overall in these two age groups is not significantly different from the performance of U.S. children. If future research demonstrates that these findings are stable across all age groups and for larger samples, the implication is that the MAP can be administered and scored in Israel with the scoring methodology and normative information developed in the United States. However, because of the poorer performance of Israeli children on the Foundations Index, we recommend that specific Israeli norms be developed.

Quality improvement in the cutaneous micrographic surgery laboratory

A nationwide advocacy for improving health-care quality--including the dimensions of efficiency, productivity, and customer satisfaction--is rapidly growing. This initiative is evolving in an environment of total quality management (TQM) and continuous quality improvement (CQI). Quality assessment and improvement (QI) is a quality management program through which laboratories ensure the quality of their health-care services by continually monitoring, evaluating, and resolving opportunities for improvement. Using a systematic, FOCUS-PDCA approach, the Mohs histology laboratory implemented improvement of the quality management of frozen-section slide production and turnaround time (TAT). The Mohs laboratory achieved improved technical process performance, faster TAT time, more efficacious patient care support, and increased customer satisfaction. Using a comprehensive quality assessment and improvement process can overwhelm quality management assets if it is not approached in a systematic, prioritized manner. However, when judiciously used, the process can become a key instrument for ensuring and improving high-quality laboratory services in an efficient manner.

A nonradioactive fluorescent gel-shift assay for the analysis of protein phosphatase and kinase activities toward protein-specific peptide substrates

Synthetic peptides are important tools with which to study the activities of protein kinases and phosphatases toward specific substrate sequences which are present within selected regions of a protein. Most existing assays for the phosphorylation or dephosphorylation of such peptides utilize 32P and either affinity chromatography or HPLC separation and require extensive characterization and validation. Here, we describe a method for monitoring the phosphorylation or dephosphorylation of almost any peptide of interest which does not require the use of radioactivity, making its reagents stable for a prolonged period, and which can be performed in any standard laboratory. For this, after performance of kinase or phosphatase reactions with the peptide of interest, products are derivatized with fluorescamine and are separated according to charge by agarose gel electrophoresis. Phosphorylated and nonphosphorylated peptides are readily separated and can be both identified and quantified by uv detection. The lower limit for detection of peptide in the agarose gel was 0.02 nmol using the gel-shift kinase assay with cAMP-dependent kinase and Kemptide as substrate. This had sensitivity and reproducibility similar to those of a standard assay using [gamma-32P]ATP with this substrate. Dephosphorylation of a synthetic phosphopeptide corresponding to a segment of the cholecystokinin receptor was tested in an analogous assay with known amounts of protein phosphatase 2A. Phosphopeptide and dephosphopeptide were easily detected and quantified with as little as 0.03 mU/ml protein phosphatase 2A activity. Therefore, with this assay, most synthetic peptides and phosphopeptides can be used as substrates without further modification. This will be of particular interest for monitoring the purification of highly specific protein kinase and phosphatase activities.

MR angiography of peripheral posterior inferior cerebellar artery aneurysms

OBJECTIVE

A small subset of posterior inferior cerebellar artery (PICA) aneurysms arise distal to the vertebral artery origin of the PICA. We present two such cases seen on conventional angiography and MR angiography (MRA).

MATERIALS AND METHODS

The findings in two patients are presented. In one the aneurysm presented with subarachnoid hemorrhage. The second was found incidentally but later ruptured.

RESULTS

There was good agreement between the appearance of the aneurysms on MRA and conventional angiography.

CONCLUSION

Awareness of the possibility of peripheral PICA aneurysms and their features is important. The positioning of the volume of excitation for MRA may have to be adjusted to include a very low PICA caudal loop.

Characterization of protein serine/threonine phosphatases in rat pancreas and development of an endogenous substrate-specific phosphatase assay

Protein phosphatases have recently been recognized to represent an important, independently regulated portion of cellular signaling cascades. Although reversible phosphorylation of multiple pancreatic proteins has been described, suggesting a role for these enzymes, little is known about the characteristics of protein phosphatases in this organ. In this work, we have characterized and quantified the serine/threonine phosphatases present in pancreatic cytosol and plasma membranes. Using a sensitive and specific in vitro assay with standard substrates (phosphorylase a and phosphocasein), the predominant enzymes represented protein phosphatase 2A in cytosol and protein phosphatase 1 in plasma membranes, with both compartments having substantial amounts of both of these enzymes. Both compartments also had protein phosphatase 2B activity, whereas protein phosphatase 2C was only measurable in the plasma membrane fraction. Further, a novel assay was developed and validated in which the action of an endogenous protein phosphatase on a specific cellular phosphoprotein was studied. For this, we utilized as substrate the cholecystokinin receptor which had been phosphorylated in response to agonist stimulation of the intact acinar cell. This type of assay will be key for the analysis of the mediation and regulation of dephosphorylation events which actually occur in the cell.

Low concentrations of protein kinase C-activating agonists suppress cholecystokinin-OPE-evoked Ca2+ mobilization in rat pancreatic acini

The phenethyl ester analogues of cholecystokinin, OPE and JMV-180, are fully efficacious rat pancreatic secretagogues which, unlike cholecystokinin (CCK), do not elicit supramaximal inhibition of secretion, and stimulate a sustained rise of cytosolic calcium ([Ca2+]i) above basal levels. We have recently shown that low-level protein kinase C (PKC) activation by preincubation of acini with 1 nM 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or minimally secreting concentrations of PKC-activating receptor agonists (1 pM CCK-8, 0.1 microM carbachol or 10 pM bombesin) cause supramaximal inhibition of OPE-stimulated enzyme secretion. We now show that treatment of acini under these conditions also suppresses the sustained rise of [Ca2+]i stimulated by OPE to basal levels in these cells, without changing the initial OPE-stimulated [Ca2+]i peak. The resultant pattern of calcium signalling is similar to that evoked by supramaximal concentrations of native CCK. This suggests that even low concentrations of PKC-activating agonists have the potential to induce inhibitory effects on Ca2+ mobilization and that this kinase is important in generating the supramaximal inhibition observed in response to CCK.

Suppression of Ca2+ oscillations induced by cholecystokinin (CCK) and its analog OPE in rat pancreatic acinar cells by low-level protein kinase C activation without transition of the CCK receptor from a high- to low-affinity state

Cholecystokinin (CCK) analogs, JMV-180 and OPE, release Ca2+ from intracellular stores and induce oscillations in the concentration of cytosolic Ca2+ ([Ca2+]i), but do not generate a detectable rise in inositol 1,4,5-trisphosphate (InsP3) levels. In contrast, high concentrations of CCK elevate InsP3, as well [Ca2+]i, to a peak which decreases to near basal levels without oscillations. The mechanisms which underlie inhibition of [Ca2+]i oscillations observed with high CCK concentrations are unclear, but are believed to involve a low-affinity CCK receptor state. Alternately, CCK analogs may be weak partial agonists of the phospholipase C pathway, whereas native CCK, as a full agonist of this pathway, stimulates low levels of protein kinase C (PKC) activity. Preincubation of acini with 1 nM 12 O-tetradecanoyl-phorbol 13-acetate (TPA) for 15 min at 37 degrees C did not affect OPE binding to acini, but abolished OPE-induced (at 1 microM) [Ca2+]i oscillations without affecting the initial [Ca2+]i spike. These transformed OPE-induced [Ca2+]i responses mimicked those induced by supramaximal CCK octapeptide (CCK-8) concentrations. Inhibition of [Ca2+]i oscillations by 1 nM TPA was reversed by the PKC inhibitor staurosporine (0.2 microM). After [Ca2+]i oscillations were induced with OPE or low concentrations of CCK-8 (20 pM), 1 nM TPA caused a gradual slowing of oscillation frequency over 15-20 min without affecting [Ca2+]i spike amplitude. In contrast, 1 microM TPA inhibited OPE binding and caused a more generalized inhibition of OPE- and CCK-evoked Ca2+ signals.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of cyclophosphamide-induced hemorrhagic cystitis with prostaglandins

OBJECTIVE

To report a case of cyclophosphamide-induced hemorrhagic cystitis, discuss prevention, and review treatment options, particularly the use of intravesicular prostaglandins.

DATA SOURCES

Literature obtained through a computerized search, with subsequent bibliography scanning. Information on the individual case was obtained from the patient's medical record and the Pharmacy Clinical Research Specialist.

CASE SUMMARY

A 29-year-old woman who had a postallogeneic bone marrow transplantation was hospitalized because of graft-versus-host disease. During hospitalization, she developed a cyclophosphamide-induced hematuria that, despite hydration and transfusions of blood products, progressed to refractory hemorrhagic cystitis. A response was prompted ultimately by a regimen consisting of continuous bladder irrigation and intermittent intravesical instillation of carboprost.

DISCUSSION

The best treatment for hemorrhagic cystitis remains prevention. Therapies for established cystitis are varied; the choice depends on the degree of hematuria present. Therapies are often temporary or ineffective, and themselves cause significant morbidity. One promising treatment option involves the intravesicular administration of prostaglandins. Reports in the literature discuss a variety of products, dosages, and treatment schedules that have been used with some success. The available data on this technique are presented.

CONCLUSIONS

Prostaglandins appear to be effective in resolving established hemorrhagic cystitis; however, their place in therapy remains unclear. Before this class can be employed routinely, several basic issues remain. These include optimal dosage, dosing schedule, duration of treatment, and comparative efficacy with other agents.

Upregulation of secretin receptor gene expression in rat cholangiocytes after bile duct ligation

Secretion stimulates ductular bile secretion by binding to receptors on intrahepatic bile duct epithelial cells (i.e., cholangiocytes). In the rat, this choleretic effect increases after bile duct ligation (BDL). Although cholangiocyte proliferation induced by BDL contributes to secretin-induced hypercholeresis, the mechanisms modulating these alterations in secretin-induced ductular bile secretion are obscure. Thus we studied the expression of secretin receptor mRNA (SR-mRNA) in purified liver cells from normal and BDL rats. Northern blot analysis and RNase protection assays with mRNA from purified liver cells demonstrated SR-mRNA only in cholangiocytes; moreover, SR gene expression showed a seven- to ninefold increase in individual cholangiocytes from BDL rats compared with controls. This increase in SR-mRNA expression was related to a similar increase in the rate of transcription of SR-mRNA in cholangiocytes from BDL rats. Thus our studies indicate that 1) SR-mRNA is detected in liver only in cholangiocytes; 2) BDL causes an increase in SR-mRNA in individual cholangiocytes; and 3) the increase in SR-mRNA after BDL is partly related to an increase in the rate of transcription of SR-mRNA by cholangiocytes after BDL. Our data suggest that upregulation of the SR gene may contribute to secretin-induced hypercholeresis.

Use of electroconvulsive therapy during pregnancy

OBJECTIVE

Untreated major mood disorders during pregnancy pose significant risks. The author reviews case reports of the use of electroconvulsive therapy (ECT) during pregnancy to clarify potential risks and modifications of ECT techniques that make the procedure safer for pregnant women.

METHODS

A total of 300 case reports of ECT during pregnancy drawn from the literature from 1942 through 1991 were reviewed.

RESULTS

Twenty-eight of the 300 cases reported complications associated with ECT during pregnancy, including transient, benign fetal arrhythmias; mild vaginal bleeding; abdominal pain; and self-limited uterine contractions. Without proper preparation, there was also increased likelihood of aspiration, aortocaval compression, and respiratory alkalosis.

CONCLUSIONS

Electroconvulsive therapy is a relatively safe and effective treatment during pregnancy if steps are taken to decrease potential risks. Preparation for ECT during pregnancy should include a pelvic examination, discontinuation of nonessential anticholinergic medication, uterine tocodynamometry, intravenous hydration, and administration of a nonparticulate antacid. During ECT, elevation of the pregnant woman's right hip, external fetal cardiac monitoring, intubation, and avoidance of excessive hyperventilation are recommended. Informed consent for ECT should include the patient's capacity to understand and rationally evaluate risks and benefits to herself and the fetus.

Mechanisms of heterologous agonist-stimulated phosphorylation of cholecystokinin receptor

The phosphorylation of one receptor that occurs as a result of the stimulation of a different receptor on a cell is a common mechanism for heterologous regulation or "cross-talk," which has been implicated in desensitization. In this work, we focus on the mechanisms of phosphorylation of the rat pancreatic acinar cell cholecystokinin (CCK) receptor that occur upon stimulation of this cell by various agonists. Phosphorylation was allowed to occur in dispersed intact acinar cells in response to the experimental manipulation, and the phosphoreceptor was subsequently purified and quantified as an indication of response. Agonists such as vasoactive intestinal polypeptide and secretin, which act via activation of adenylate cyclase, had no effect on CCK receptor phosphorylation, whereas carbamylcholine and bombesin stimulated increased phosphorylation of the CCK receptor. Because these agents would be expected to activate protein kinase C (PKC) as well as a number of calcium-sensitive kinases and phosphatases, these activities were further dissociated by using more direct activators and inhibitors acting intracellularly. Manipulation of calcium independent of PKC by using a calcium ionophore, inhibition of calcium/calmodulin-dependent kinase II, and inhibition of calcium-dependent protein phosphatase type 2B had no effect on the state of CCK receptor phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

The preparation of frozen sections for micrographic surgery. A review of current methodology

BACKGROUND

Various methods are currently in use for preparing histological slides for micrographic surgery.

OBJECTIVE

Because many variables contribute to the quality preparation of frozen sections, a review of techniques available is useful to the Mohs surgeon. TECHNICAL METHODS AND RESULTS: Our techniques as well as the published work of others regarding mounting, embedding, freezing, slides, fixation, staining, and clearing are reviewed in detail. By the use of the options selected we were able to produce, in a short turn-around time, frozen sections with excellent quality and minimal artifact.

CONCLUSION

Presently all preparation techniques may introduce some degree of artifact. However, we feel the process described herein is adaptable to all Mohs surgery laboratories and will result in high quality specimens with minimal artifact.

Intrinsic photoaffinity labeling of native and recombinant rat pancreatic secretin receptors

BACKGROUND

Structural characterization of pancreatic secretin receptors has been limited by difficulties in generating suitable radioligands and obtaining sufficient substrate. The aims of this study were to design, synthesize, and characterize high affinity radiolabeled analogues of secretin suitable for "intrinsic" photoaffinity labeling and to clone, express, and characterize the recombinant rat pancreatic secretin receptor.

METHODS

The ability of synthetic analogues to stimulate amylase secretion by pancreatic acini was studied. Receptor complementary DNA (cDNA) was cloned by screening a rat pancreatic library with a probe based on the sequence of a neural cell secretin-binding protein. Competition binding and affinity labeling were performed with membranes prepared from rat pancreas and transfected cells.

RESULTS

Two probes were fully efficacious secretagogues, which bound in a specific, high-affinity, rapid, and temperature-dependent manner. Only ([125I]Tyr10, pNO2-Phe22) rat secretin 27 covalently labeled a 50,000-62,000-molecular weight pancreatic membrane protein, with labeling inhibited in a concentration-dependent manner by secretin but not vasoactive intestinal polypeptide. Hybridization screening yielded a full-length cDNA identical to the neural clone. Photoaffinity labeling of this recombinant receptor identified a 57,000-62,000-molecular weight protein with specificity similar to that of native pancreas. Both native and recombinant receptors migrated at a molecular weight of 42,000 after endoglycosidase F deglycosylation.

CONCLUSIONS

This study provides evidence for the molecular identity of the pancreatic secretin receptor and presents a novel probe important in structural characterization of its agonist-binding domain.

Control of cholecystokinin receptor dephosphorylation in pancreatic acinar cells

Phosphorylation of cell surface receptors regulates the physiological response to many hormones and neurotransmitters. We have demonstrated that the receptor for cholecystokinin (CCK), the major secretagogue for the exocrine pancreas, is phosphorylated on serines in response to CCK (Klueppelberg, U.G., Gates, L.K., Gorelick, F.S., and Miller, L.J. (1991) J. Biol. Chem. 266, 2403-2408). Receptor phosphorylation was transient, even in the continued presence of agonist, and suggested a role for pancreatic protein phosphatases (PP) in regulating receptor phosphorylation in the intact cell. Treatment of acinar cells with okadaic acid increased the extent and duration of receptor phosphorylation induced by CCK. Receptor phosphorylated in the intact cell in response to CCK was used as substrate to analyze protein phosphatases in pancreatic acinar cell extracts. The predominant CCK receptor phosphatase activity was found in the cytosol and was potently inhibited by okadaic acid (IC50 = 0.2 nM). This phosphatase activity was unaffected by inhibitor-2, Ca2+, or Mg2+, suggesting that the major receptor phosphatase was PP-2A. Stimulation of cells with CCK resulted in a 3-fold increase in protein phosphatase activity toward the CCK receptor, at the same time that phosphorylase a phosphatase activity was unchanged. This increase in receptor phosphatase activity was reflected only in the cytosol, with the particulate activity unchanged. Consistent with this subcellular localization, the hormone-regulated receptor phosphatase activity was PP-2A, with chromatographic separation demonstrating activity in both PP-2A1 and PP-2A2 forms. These data suggest that CCK coordinates the activity of both protein kinases and phosphatases acting on the CCK receptor to control the extent and duration of receptor phosphorylation in the pancreatic acinar cell.

Molecular cloning and functional expression of the human gallbladder cholecystokinin A receptor

Through binding to cholecystokinin (CCK) A receptors, CCK is an important physiologic regulator of both gallbladder contraction and pancreatic enzyme secretion. In this work, we have used a combination of hybridization screening of a cDNA library and polymerase chain reaction to clone a 2.1 kb cDNA which encodes the human gallbladder CCKA receptor. Nucleotide sequence analysis revealed an open reading frame encoding a 428 amino acid protein, with seven putative transmembrane domains and a high degree of homology with the rat CCKA receptor. COS cells transfected with this cDNA clone bound CCK-8 and L-364,718 with high affinities appropriate for the CCKA receptor, and exhibited a transient increase in intracellular calcium in response to CCK. This should provide an important resource for the analysis of the role of this receptor in human physiology and pathophysiology.

A role for cholecystokinin-stimulated protein tyrosine phosphorylation in regulated secretion by the pancreatic acinar cell

Cholecystokinin (CCK) is a gastrointestinal hormone that acts through a G protein-coupled receptor to stimulate pancreatic enzyme secretion. In this work, we demonstrate that CCK stimulation of dispersed pancreatic acini results in increased tyrosine phosphorylation of several cellular proteins. This is mediated via a calcium-dependent pathway, also activated by a phenethyl ester analogue of CCK and calcium ionophores, and by a protein kinase C-dependent cascade, also activated by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate. All demonstrable stimulated tyrosine phosphorylation events were inhibited by genistein, with different subsets of proteins affected by staurosporine and H-7. The importance of tyrosine phosphorylation events in agonist-stimulated amylase secretion was studied using genistein and staurosporine as protein kinase inhibitors. Genistein inhibited the secretory response to CCK, its phenethyl ester analogue, and calcium ionophores, all known to stimulate secretion in a calcium-dependent fashion. In contrast, genistein had no effect on the secretory response to 12-O-tetradecanoylphorbol-13-acetate, suggesting that the protein kinase C-dependent tyrosine phosphorylation events were not involved in the secretory mechanism. Furthermore, CCK-induced secretion was not affected by relatively specific protein kinase C inhibition by H-7, but was decreased by staurosporine, an inhibitor of both protein kinase C and tyrosine kinase activities in these cells. These results provide evidence that acinar cell tyrosine phosphorylation is stimulated by agonists acting via calcium-dependent and protein kinase C-dependent pathways, with only the calcium-dependent tyrosine phosphorylation cascade involved in triggering hormone-induced amylase release.

Nedocromil sodium

OBJECTIVE

To summarize the available pharmacokinetic and pharmacologic data on nedocromil sodium and to present representative clinical trials of this new agent in both mild-to-moderate and severe chronic asthma and allergic rhinitis. Adverse effects are reviewed.

DATA SOURCES

A MEDLINE search was used to identify pertinent literature, excluding reviews and foreign-language articles. All available English-language studies were reviewed.

DATA EXTRACTION

Pivotal and representative studies are discussed relating to the following issues: pharmacology and pharmacokinetics, management of patients with non-steroid-dependent and steroid-dependent asthma, comparison with sodium cromoglycate (cromolyn), comparison with inhaled beclomethasone dipropionate, management of exercise-induced asthma, use in children with asthma, and use in allergic rhinitis.

DATA SYNTHESIS

Nedocromil sodium is chemically grossly unrelated to cromolyn but has similar pharmacology, pharmacokinetics, and therapeutic benefits. Although ineffective in relieving acute asthma attacks, nedocromil appears to be superior to placebo in lessening the severity of chronic asthma and protecting against allergen-induced asthma when taken as chronic prophylaxis. Single doses attenuate exercise-induced asthma. It is also effective in the management of allergic rhinitis. Results have varied when nedocromil has been compared with cromolyn or inhaled beclomethasone. Studies to date indicate that, overall, nedocromil is not significantly better than cromolyn and is no better than or is inferior to inhaled beclomethasone, although individual response appears to be variable, with no identifiable predictive factors.

CONCLUSIONS

Individual patients may receive marked improvement from nedocromil therapy, but there are no factors that identify which patients will respond. Nedocromil may be particularly useful in adults who frequently fail to respond to cromolyn.

Multiple kinases phosphorylate the pancreatic cholecystokinin receptor in an agonist-dependent manner

The cholecystokinin (CCK) receptor on the rat pancreatic acinar cell is a guanine nucleotide-binding protein (G protein)-coupled receptor, which was recently demonstrated to be phosphorylated in response to agonist stimulation (Klueppelberg et al., J. Biol. Chem. 266: 17744-17746, 1991). In this work, we establish that this receptor is phosphorylated in response to a variety of homologous and heterologous secretagogues and that these phosphorylation events represent action by more than one protein kinase. One subgroup of kinases includes one or more isotype of protein kinase C (PKC), and is capable of playing a role in homologous and heterologous desensitization. A second subgroup of kinases that acts on the CCK receptor was defined by its resistance to 10 microM staurosporine, which was shown to inhibit all PKC in these cells. The activity of the second group of kinases was observed only in response to occupation of the CCK receptor by high concentrations of native hormone, raising the possibility of a "receptor-specific kinase." Similar to the prototypical kinase, beta-adrenergic receptor kinase (beta-ARK), this activity was inhibited in permeabilized cells by heparin. Furthermore, like this enzyme activity, beta-ARK was shown to be resistant to staurosporine. Based on its action on a G protein-coupled receptor, its activation at high concentrations of native agonist, and its pattern of inhibition, we believe that the staurosporine-insensitive CCK receptor kinase activity represents either beta-ARK or a closely related member of the receptor-specific kinase enzyme family.