Amylase release from streptolysin O-permeabilized pancreatic acini

Intracellular mediators of exocytosis were investigated using isolated mouse pancreatic acini permeabilized with the bacterial toxin streptolysin O (SLO). Permeabilization was demonstrated by fluorescent staining with ethidium bromide and fluorescein diacetate and release of cytoplasmic lactate dehydrogenase. When SLO-permeabilized acini were incubated at 37 degrees C in Ca2(+)-EGTA buffers containing MgATP, amylase secretion was Ca2+ dependent with an EC50 of 0.40 microM Ca2+ and a maximally effective Ca2+ concentration of 1 microM. Maximal amylase secretion was 330% of that in Ca2(+)-free buffer (basal). The nonhydrolyzable GTP analogue guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S; 30 microM) increased the maximal secretion to 451% of basal in the presence of 1 microM Ca2+ and decreased the EC50 to 0.14 microM Ca2+. Removal of ATP plus addition of antimycin A and 2-deoxy-D-glucose inhibited Ca2(+)-dependent, GTP gamma S-enhanced amylase secretion by 56%. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA; 1 microM) also enhanced maximal secretion to 450% of basal and decreased the EC50 to 0.18 microM Ca2+. Enhancement of amylase secretion by submaximal concentrations of GTP gamma S or TPA was inhibited by the protein kinase C inhibitor staurosporine. These results suggest that Ca2+ stimulation of amylase secretion is potentiated by activation of protein kinase C. However, the enhancement of secretion by GTP gamma S and TPA was additive at their maximally effective concentrations, suggesting that another G protein(s) maybe involved in the terminal steps of exocytosis.

Cholecystokinin: A Key Integrator of Nutrient Assimilation

Cholecystokinin regulates numerous gastrointestinal functions including pancreatic enzyme and fluid secretion and gastric emptying. Pleiotropic actions of cholecystokinin result in coordination of several aspects of ingestion, digestion, absorption, and metabolism. Integration of nutrient assimilation through regulation of these functions is an important physiological role of cholecystokinin.

Genetic and molecular analysis of vgU and vgW: two dominant vg alleles associated with gene fusions in Drosophila

In the absence of a vg+ gene, extensive cell death occurs in third instar imaginal discs, which results in a complete loss of adult wing margin structures. Essentially all molecularly characterized vg alleles are associated with deletions or insertions of DNA into the vg locus. These alterations reduce or eliminate a 3.8-kb vg-specific transcript, resulting in recessive loss of function alleles. We report here the analysis of two dominant vg alleles which have been identified (vgU and vgW). The vgU allele is associated with a chromosomal inversion which splits the vg locus, resulting in a gene fusion between vg and the mastermind (mam) neurogenic locus. Reversion analysis of vgU indicates that sequences from the mam locus are required for vgU dominance. The vgW allele is also the result of a chromosomal inversion, in this case resulting in a gene fusion between vg and the homeobox-containing invected (inv) gene. It is also associated with novel dominant homeotic transformations. Revertant analysis indicates that sequences from inv are required for the dominant wing and dominant homeotic effects of vgW. The vg dominance does not appear to be mediated through a reduction of vg expression or a novel fusion transcript in either vgU or vgW. The results are consistent with a model in which inappropriate expression of inv causes the dominant homeotic effects seen in vgW.

Growing pancreatic acinar cells (postpancreatitis and fetal) express a ductal antigen

Monoclonal antibodies specific for luminal plasma membranes of acinar and duct cells of the exocrine pancreas were used to investigate changes in antigen expression during regeneration of the pancreas after acute pancreatitis and during fetal pancreatic development in mice. During regeneration after acute pancreatitis induced by supramaximal injections of cerulein or by a choline-deficient, ethionine-supplemented diet, morphologically identifiable acinar cells expressed the ductal antigen on their luminal surface, but at a lower level than this antigen is expressed on duct cells. As the pancreas regenerated, the ductal antigen was lost from acinar cells and was found only on duct cells. Characteristic tubular complexes formed in both pancreatitis models and were positive for the acinar antigen, demonstrating their acinar origin. In fetal pancreas, acinar cells between prenatal days 3 through 1, when zymogen granules were already abundant, expressed the duct-cell antigen on their luminal surface. By birth duct antigen was mostly present on ducts with only occasional label on acinar cells. The presence of a ductal antigen on acinar cells is associated with acinar-cell growth during regeneration and during fetal development and may reflect a less differentiated state.

Inhibition of platelet adhesion to surfaces of extracorporeal circuits by disintegrins. RGD-containing peptides from viper venoms

Previous studies indicate that exposure of fibrinogen receptors associated with glycoprotein IIb/IIIa complex contributes to platelet loss during cardiopulmonary bypass. Recently, we isolated a number of RGD (Arg-Gly-Asp)-containing, low molecular weight, cysteine-rich peptides from viper venoms. These peptides, which we propose to call "disintegrins," block platelet-fibrinogen interaction and platelet aggregation. We compared the effect of RGDS (Arg-Gly-Asp-Ser) and four disintegrins (echistatin, flavoridin, albolabrin, and bitistatin) on platelet behavior in a membrane oxygenator. During simulated extracorporeal circulation for 2 hours, platelet count decreased to about 30% of initial values. Addition of echistatin (60-200 nM), albolabrin (60-200 nM), bitistatin (60 nM), and flavoridin (45 nM) significantly inhibited platelet loss in the circuit. RGDS (33 microM) did not show any significant inhibitory effect. ADP-induced platelet aggregation was inhibited in samples of platelet-rich plasma taken from the circuits containing disintegrins. However, echistatin appeared to be a more potent inhibitor of platelet aggregation, whereas albolabrin and flavoridin interfered more selectively with platelet loss from the circuit. Echistatin prevented the accumulation of glycoprotein IIIa on the surface of the circuit. Echistatin (60-200 nM), flavoridin (45 nM), bitistatin (60 nM), and albolabrin (200 nM) significantly inhibited the loss of beta-thromboglobulin from platelets into circulating plasma. Electron microscopy studies demonstrated shape change but not degranulation in platelets circulating in the presence of 200 nM echistatin. On the other hand, this peptide (up to 1,000 nM) did not prevent loss of alpha granules and beta-thromboglobulin from thrombin-stimulated platelets, although it prevented their aggregation. In conclusion, disintegrins protect platelets in the circuit by preventing their adhesion to surfaces and, therefore, preventing fragmentation of adhered platelets under the shear stress of flowing blood. This study indicates that disintegrins may be potential candidates for platelet protection during cardiopulmonary bypass.

Gastrointestinal peptides activate Na(+)-H+ exchanger in AR42J cells by increasing its affinity for intracellular H+

Regulation of intracellular pH (pHi) was studied by dual wavelength fluorometry in monolayers of pancreatic AR42J cells loaded with the fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. In cells superfused with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solution at pH 7.40, basal pHi was determined to be 7.15 +/- 0.13. Na(+)-H+ exchange could be demonstrated in both resting cells and cells subjected to acid loading by use of transient exposure to NH4Cl. Na(+)-H+ exchange was completely blocked by 300 microM amiloride and was dependent on extracellular Na+ (apparent Km = 25 mM). When the concentration of the NH4Cl pulse was varied (0.5-25 mM), the rate of pHi recovery increased as pHi became acidic, reaching a maximum of 0.007 pH units/s at pHi of 6.4. Gastrointestinal hormones, including pentagastrin, cholecystokinin, and bombesin, increased the rate of Na(+)-H+ exchange without affecting cellular buffer capacity (21.5 +/- 1.8 mM/pH unit), thereby leading to an intracellular alkalinization. This was accompanied by a shift in the curve of Na(+)-H+ exchange as a function of pHi to more alkaline values, although the maximum rate of pH recovery was unchanged. Neither protein kinase C nor Ca2+ could be conclusively linked to activation of Na(+)-H+ exchange, raising the possibility of a more direct, receptor-controlled mechanism.

Targeting of human glioma xenografts in vivo utilizing radiolabeled antibodies

Radiolabeled antibodies provide a potential basis for selective radiotherapy of human gliomas. We have measured tumor targeting by radiolabeled monoclonal and polyclonal antibodies directed against neuroectodermal and tumor-associated antigens in nude mice bearing human glioma xenografts. Monoclonal P96.5, a mouse IgG2a immunoglobulin, defines an epitope of a human melanoma cell surface protein, and specifically binds the U-251 human glioma as measured by immunoperoxidase histochemistry. 111In-radiolabeled P96.5 specifically targets the U-251 human glioma xenograft and yields 87.0 microCuries (microCi) of tumor activity per gram per 100 microCi injected activity compared to 4.5 microCi following administration of radiolabeled irrelevant monoclonal antibody. Calculations of targeting ratios demonstrate deposited dose to be 11.6 times greater with radiolabeled P96.5 administration compared to irrelevant monoclonal antibody. The proportion of tumor dose found in normal organs is less than 10%, further supporting specific targeting of the human glioma xenograft by this antibody. Monoclonal antibody ZME018, which defines a second melanoma-associated antigen, and polyclonal rabbit antiferritin, which defines a tumor-associated antigen, demonstrate positive immunoperoxidase staining of the tumor, but comparatively decreased targeting. When compared to the 111In-radiolabeled antibody, 90Y-radiolabeled P96.5 demonstrates comparable tumor targeting and percentages of tumor dose found in normal organs. To test the therapeutic potential of 90Y-radiolabeled P96.5, tumors and normal sites were implanted with miniature thermoluminescent dosimeters (TLD). Seven days following administration of 100 microCi 90Y-radiolabeled P96.5, average absorbed doses of 3770, 980, 353, and 274 cGy were observed in tumor, liver, contralateral control site, and total body, respectively. Shared cell surface antigens among neuroectodermally derived neoplasms provide a basis for exploration of human glioma radioimmunotherapy.

Structural characterization of Y1 and Y2 receptors for neuropeptide Y and peptide YY by affinity cross-linking

Pharmacological studies indicate that peptide YY (PYY) and neuropeptide Y interact with multiple binding sites, categorized as Y1 and Y2 subtypes. In order to identify and structurally characterize the Y1 and Y2 receptors we covalently cross-linked [125I-Tyr36]PYY to its receptors. The Y2 receptor in rat hippocampus and rabbit kidney membranes was affinity labeled using different homo- and heterobifunctional cross-linking reagents. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography resulted in a major labeled protein band of Mr = 50,000 in both hippocampal and kidney membranes, which was unaffected by reducing agents. The Y1 receptor was analyzed in membranes from the MC-IXC human neuroblastoma cell line. Autoradiography revealed two labeled bands at Mr = 70,000 and 45,000. As the intensity of the Mr = 45,000 band was reduced by protease inhibitors, it is likely that this band is a degradation product of the larger band. Labeling of these proteins was obtained only when N-5-azido-2-nitrobenzoyloxysuccinimide was employed for cross-linking followed by exposure to UV light. Labeling of the two cross-linked bands was unaffected by reducing agents. The binding of radiolabeled PYY and the intensity of the cross-linked bands, for both the Y1 and Y2 receptors, were inhibited similarly in a dose-dependent manner by increasing concentrations of unlabeled PYY. When exposed to agarose-coupled lectins, the detergent-solubilized Y1 receptor-hormone complex was completely adsorbed by wheat germ agglutinin and partially by ricin communis II. The cross-linked Y2 receptor was almost totally adsorbed by wheat germ agglutinin-agarose and partially adsorbed by concanavalin A. The adsorptions were in all cases blocked by the appropriate hapten sugar. These results indicate that the Y1 receptor is a glycoprotein with a Mr = 70,000 binding subunit, whereas the Y2 receptor is a glycoprotein with a Mr = 50,000 binding subunit. These results provide evidence that the Y1 and Y2 subtypes of neuropeptide Y and PYY receptors, previously characterized pharmacologically, are structurally distinct glycoproteins, not disulfide-linked to other subunits.

The radiopacity of glass ionomer dental materials

Although some glass ionomer dental materials are described as radiopaque by the manufacturer, it is rare for the actual degree of radiopacity to be specified. Using a technique previously described for measurement of the radiopacity of enamel, dentine and composite resin dental materials, the radiopacity of a number of glass ionomer materials, including restorative, lining and luting cements, was determined.

Hours, volume, and type of work of preregistration house officers

OBJECTIVE

To determine the hours, volume, and type of work undertaken by preregistration house officers.

DESIGN

Continuous observation of 472 hours of work performed by 12 preregistration house officers based in medical wards, using standard procedures for studying work patterns.

SETTING

A teaching hospital with 340 beds assigned to general medicine and coronary care.

SUBJECTS

12 Of the 16 preregistration house officers in medicine at the hospital.

MAIN OUTCOME MEASURES

The hours, volume, and type of work undertaken by preregistration house officers in February 1989, as recorded by trained observers on a one to one basis.

RESULTS

The hours of duty ranged from 83 to 101 hours each week, the longest period of continuous duty being 58 hours. Each shift, house officers spent up to 25 minutes travelling between wards and an average of 85 minutes treating patients in wards that were cross covered. Between 50% and 71% of house officers' time was spent on patient oriented duties during the day; this fell to between 21% and 53% at night. Each doctor spent an average of 40 minutes filing when off duty after 6 pm.

CONCLUSIONS

Established procedures for studying workload were effective in monitoring doctors' hours, providing accurate information on the volume and type of work, which is essential to resolve the problems of medical staffing. The study showed that more house officers were needed and that the cross cover system should be stopped. As a result three extra preregistration house officers were appointed.

Two functionally distinct cholecystokinin receptors show different modes of action on Ca2+ mobilization and phospholipid hydrolysis in isolated rat pancreatic acini. Studies using a new cholecystokinin analog, JMV-180

A new hepatapeptide cholecystokinin (CCK) analog, JMV-180 (Boc-Tyr(SO3-)-Nle-Gly-Trp-Nle-Asp-2-phenylethylester), acts as an agonist at high affinity CCK receptors on rat pancreatic acini to stimulate amylase release but unlike cholecystokinin octapeptide (CCK8) does not act on low affinity CCK receptors to inhibit amylase release (Galas, M. D., Lignon, M. F., Rodriguez, M., Mendre, C., Fulcrand, P., Laur, J., and Martinez, J. (1988) Am. J. Physiol. 254, G176-G188). To investigate the biochemical mechanisms initiated by CCK acting on each class of CCK receptor, the effects of JMV-180 and CCK8 on amylase release, Ca2+ mobilization, and phospholipid hydrolysis were studied in isolated rat pancreatic acini. When acini were loaded with the intracellular Ca2+ chelator BAPTA, amylase release stimulated by both JMV-180 and CCK8 was reduced. Measurement of 45Ca2+ efflux and cytosolic free calcium concentration ([Ca2+]i) by the fluorescence of fura-2-loaded acini in a stirred cuvette showed that JMV-180 induced a concentration-dependent increase but with a maximal response only two-thirds that induced by CCK8. When [Ca2+]i of individual fura-2-loaded acinar cells was measured by microspectrofluorometry, all concentrations of JMV-180 (1 nM-10 microM) induced repetitive transient [Ca2+]i spikes (Ca2+ oscillations). By contrast, stimulation with a high concentration of CCK8 (1 nM) caused a large increase in [CA2+]i followed by a small sustained elevation of [Ca2+]i. The measurement of inositol trisphosphate (IP3) production by both [3H]inositol labeling and 1,4,5-IP3 radioreceptor assay showed that JMV-180 had only minimal effects at 10 microM in contrast to the large increase induced by high concentrations of CCK8 (more than 1 nM). JMV-180 blocked the effect of a high concentration of CCK8 on both [Ca2+]i and 1,4,5-IP3 productions but did not affect the response to carbamylcholine. JMV-180 caused a delayed monophasic stimulation of 1,2-diacylglycerol (DAG) sustained to 60 min without the early increase in DAG observed in response to CCK8. Furthermore, JMV-180 stimulated the release of [3H]choline metabolites, primarily phosphorylated choline, from [3H]choline-labeled acini at low concentrations and to the same extent as CCK8. Since JMV-180 interacts not only with high affinity CCK receptors as an agonist but also with low affinity CCK receptors as a functional antagonist, the present results indicate that the occupancy of high affinity state receptors by CCK induces Ca2+ oscillations, DAG formation from phosphatidylcholine hydrolysis, and amylase release with minimal phosphatidylinositol 4,5-bisphosphate hydrolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of cholecystokinin secretion by food, hormones, and neural pathways in the rat

Regulation of cholecystokinin (CCK) secretion was studied in conscious unrestrained rats by simultaneous duodenal perfusion with foodstuffs, intravenous infusion of hormones or neural agents, and arterial blood sampling for CCK bioassay. Duodenal infusion of casein resulted in elevation of plasma CCK from fasting level of 0.5 +/- 0.1 to 3.8 +/- 0.4 pM. Casein hydrolysate, calcium, and glucose did not elevate plasma CCK. Infusion of intact fat had a small, but nonsignificant, effect (1.4 +/- 0.4 pM), whereas infusion of oleate increased plasma CCK to 3.7 +/- 0.6 pM. Thus intact protein and fatty acids are the major dietary intestinal stimuli for CCK release in the rat. The CCK response to protein could be inhibited by somatostatin but not by peptide YY (0.2, 2, or 20 micrograms.kg-1.h-1); intravenous infusion of 1 or 10 micrograms.kg-1.h-1 somatostatin decreased casein-stimulated CCK levels to 1.5 +/- 0.2 and 0.9 +/- 0.3 pM, respectively. Stimulation of vagal discharge with 2-deoxy-D-glucose had no effect on basal or protein-stimulated plasma CCK levels; thus CCK release in the rat does not appear to be modulated by central vagal pathways. Gastrin-releasing peptide increased fasting plasma CCK levels to 1.6 +/- 0.1 pM. Administration of the cholinergic agonist bethanechol, while having no effect on fasting CCK level, inhibited protein-stimulated plasma CCK from 3.9 +/- 0.6 to 1.3 +/- 0.3 pM. Cholinergic blockade with atropine, in contrast, had no effect on basal or protein-stimulated plasma CCK. Thus CCK release is stimulated by dietary protein or fatty acid and by gastrin-releasing peptide and inhibited by somatostatin and bethanechol.

The functional organization of the vestigial locus in Drosophila melanogaster

Vestigial mutants are associated with imaginal disc cell death which results in the deletion of adult wing and haltere structures. The vestigial locus has previously been cloned, and mutational lesions associated with a number of vg alleles were mapped within a 19 kb DNA region defined as essential for vg function. Herein we report the identification and characterization of a developmentally regulated 3.8 kb vg transcript which is spliced from exons distributed throughout the essential interval defined above. All the characterized classical alleles have predictable effects on this transcription unit, and the severity of this effect is directly proportional to the severity of the wing phenotype. A repetitive domain within this transcription unit was identified and may serve as a tag to isolate other genes with functions related to vg. We also report an exceptional vg allele (vg83b27) that produces an extreme wing and haltere phenotype, but which defines a second vg complementation unit. This allele is associated with a 4 kb deletion entirely within a 4.5 kb vg intron as defined by the 3.8 kb transcription unit. Molecular and genetic evidence indicates that the vg83b27 mutation has a functional 3.8 kb transcription unit, thus accounting for its ability to complement classical alleles. The results indicate that sequences within a vg intron are essential for normal wing and haltere development.

Targeting and therapy of human glioma xenografts in vivo utilizing radiolabeled antibodies

Radiolabeled antibodies provide a potential basis for selective radiotherapy of human gliomas. We have measured tumor targeting by radiolabeled monoclonal antibodies directed against neuroectodermal and tumor-associated antigens in nude mice bearing human glioma xenografts. Monoclonal P96.5, a mouse IgG2a immunoglobulin, defines an epitope of a human melanoma cell surface protein and specifically binds the U-251 human glioma as measured by immunoperoxidase histochemistry. IIIIn-radiolabeled P96.5 specifically targets the U-251 human glioma xenograft and yields 87.0 microCi of tumor activity/g/100 microCi injected activity compared to 4.5 microCi following administration of 100 microCi radiolabeled irrelevant monoclonal antibody. Calculations of targeting ratios demonstrate the deposited dose to be 11.6 times greater with radiolabeled P96.5 administration compared to irrelevant monoclonal antibody. The dose found in normal organs is less than 20% of that in the tumor, further supporting specific targeting of the human glioma xenograft by this antibody. Monoclonal antibody ZME018, which defines a second melanoma-associated antigen, demonstrates positive immunoperoxidase staining of the tumor, but comparatively decreased targeting. To test the therapeutic potential of 90Y-radiolabeled P96.5 and ZME018, tumors and normal sites were implanted with miniature thermoluminescent dosimeters. Average absorbed doses of 3770 +/- 445 (SEM) and 645 +/- 48 cGy in tumor, 353 +/- 41 and 222 +/- 13 cGy in a contralateral control i.m. site, 980 +/- 127 and 651 +/- 63 cGy in liver, and 275 +/- 14 and 256 +/- 18 cGy in total body were observed 7 days following administration of 100 microCi 90Y-radiolabeled P96.5 and ZME018, respectively. Calculations of absorbed dose by the medical internal radiation dose method confirmed thermoluminescent dosimeter absorbed dose measurements. To test the therapeutic potential, tumor-bearing nude mice were given intracardiac injections of either buffer or 90Y-radiolabeled P96.5 or ZME018. Tumor regression was measured in 1 of 12, 9 of 10, and 12 of 12 compared to 0 of 10, 1 of 10, and 2 of 10 animals following administration of 50, 100, or 200 microCi 90Y-labeled P96.5 and ZME018, respectively. Average maximal decreases in tumor volume were 42.7 +/- 11.9 and 94.2 +/- 3.3% 28 and 58 days following 100 and 200 microCi 90Y-radiolabeled P96.5 administration, respectively. In contrast, no average decrease in tumor volume was noted following 50, 100, or 200 microCi 90Y-labeled ZME018.(ABSTRACT TRUNCATED AT 400 WORDS)

Oscillatory mode of calcium signaling in rat pancreatic acinar cells

Cytoplasmic free calcium concentration ((Ca2+]i) was evaluated by dual-wavelength microspectrofluorometry of fura-2-loaded individual rat pancreatic acinar cells. Resting [Ca2+]i in unstimulated acini was 94.1 +/- 4.1 nM. Stimulation with high concentrations of cholecystokinin (CCK, 100 pM to 1 nM) led to an immediate rise in [Ca2+]i to 400-1,000 nM followed by a fall within 2-5 min to a plateau only slightly above the prestimulation level. Lower and more physiological concentrations of CCK (1-30 pM), after a latent period of 60-90 s, induced a smaller sustained increase in [Ca2+]i (30-40 nM) with superimposed repetitive transient [Ca2+]i spikes. These oscillations averaged 120-150 nM in amplitude, occurred at a frequency which averaged 1.5 times/min, and were maintained as long as the stimulus was applied. Similar [Ca2+]i oscillations were observed when acini were stimulated with submaximal concentrations of carbamylcholine (0.1-1 microM) and neuromedin C (0.1-1 nM). Intracellular Ca2+ stores were not depleted during [Ca2+] oscillations, since a subsequent increase to 1 nM CCK led to an immediate rise in [Ca2+]i indistinguishable from the response of cells initially stimulated at this concentration. Although extracellular Ca2+ was required for maintenance of frequency of the spikes, the major source of Ca2+ utilized for oscillations was intracellular, since elimination of medium Ca2+ or Ca2+ entry blockade with lanthanum failed to inhibit oscillations. Vasoactive intestinal polypeptide (10 nM) and high K+ (50 mM) did not affect [Ca2+]i oscillations. Antimycin (10 microM), which depletes cytoplasmic ATP, increased basal [Ca2+]i and inhibited the oscillations.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of Ca2+ mobilizing receptors in Xenopus oocytes: a tool for receptor characterization

In order to investigate the molecular characteristics of gastrointestinal hormone receptors, we have expressed their mRNAs in Xenopus laevis oocytes. Xenopus oocytes possess intrinsic muscarinic cholinergic receptors which couple to intracellular Ca2+ release. Release of intracellular Ca2+ was detected by an increase in 45Ca2+ release from preloaded oocytes or by using the Ca2+-sensitive fluorescent dye fura-2. Similarly, cholecystokinin (CCK) receptors expressed on the surface of oocytes which were injected with mRNA prepared from rat pancreatic acinar AR42J cells were readily detected by their ability to mobilize intracellular Ca2+. The CCK receptors expressed in oocytes showed similar binding characteristics as the native receptors. CCK receptor expression in the oocytes could be specifically blocked by hybridizing the mRNA with antisense oligonucleotides based on the highly conserved second transmembrane region of the HM4 muscarinic cholinergic receptor before injection. These latter results strongly suggest that the CCK receptor is a member of the G protein-linked receptor family. Thus, expression in Xenopus laevis oocytes provides a powerful tool for elucidation of the molecular characteristics of gastrointestinal hormone receptors.

Endogenous cholecystokinin does not decrease food intake or gastric emptying in fasted rats

To investigate the hypothesized inhibitory effect of cholecystokinin (CCK) released from the small intestine on food intake and gastric emptying, we infused soybean trypsin inhibitor (STI) into the stomach or duodenum of male rats deprived of food for 17 h. Intraduodenal infusions of STI (100-200 mg) before real or sham feeding, or during sham feeding, had no effect on food intake. Intragastric infusions of STI (100-200 mg) also had no effect on gastric emptying. Identical infusions of STI, however, increased bioassayable plasma CCK six to ninefold. The failure of endogenous, small intestinal CCK released by STI to decrease food intake or to decrease gastric emptying is evidence against the hypothesis that the inhibitions of food intake and of gastric emptying are physiological functions of small intestinal CCK in food-deprived rats. In contrast to the negative results with STI, administration of exogenous CCK-8 (2-4 micrograms/kg ip) significantly inhibited food intake and gastric emptying despite producing smaller increases of plasma CCK than STI produced. The reason for the differential effects of exogenous and endogenous CCK is not clear and requires further investigation.

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

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.

Multiple sources of 1,2-diacylglycerol in isolated rat pancreatic acini stimulated by cholecystokinin. Involvement of phosphatidylinositol bisphosphate and phosphatidylcholine hydrolysis

Changes in the cellular content of 1,2-diacylglycerol (DAG) in isolated rat pancreatic acini in response to agonist stimulation were studied using a sensitive mass assay. When acini were stimulated by 10 nM COOH-terminal cholecystokinin-octapeptide (CCK8), the increase in DAG was biphasic, consisting of an early peak at 5 s and a second, larger, gradual increase that was maximal by 15 min. The basal level of DAG in acini was 1.04 nmol/mg of protein, which was increased to 1.24 nmol/mg of protein at 5 s and 2.76 nmol/mg of protein at 30 min. In comparison, the increase in DAG stimulated by 30 pM CCK8, a submaximal concentration for amylase release, was monophasic, increasing without an early peak but sustained to 60 min. Other Ca2+-mobilizing secretagogues such as carbamylcholine and bombesin increased DAG in acini, whereas vasoactive intestinal peptide, which acts to increase cAMP, had no effect. Phorbol ester and Ca2+ ionophore also stimulated DAG production. Analysis of the mass level of inositol 1,4,5-trisphosphate (1,4,5-IP3) showed that the generation of 1,4,5-IP3 stimulated by 10 nM CCK8 peaked at 5 s, a finding consistent with the early peak of DAG. The basal level was 4.7 pmol/mg of protein, which was increased to 144.6 pmol/mg of protein at 5 s by 10 nM CCK8. The levels of 1,4,5-IP3 then returned toward basal in contrast to the gradual and sustained increase of DAG. The dose dependencies of 1,4,5-IP3 and DAG formation at 5 s with respect to CCK8 were almost identical. This suggests that phosphatidylinositol 4,5-bisphosphate hydrolysis is a major source of the early increase in DAG but not of the sustained increase in DAG. Therefore, a possible contribution of phosphatidylcholine hydrolysis to DAG formation was examined utilizing acini prelabeled with [3H]choline. CCK8 (1 nM) maximally increased [3H]choline metabolite release by 133% of control at 30 min. Separation of these metabolites by thin layer chromatography showed that the products of CCK8-stimulated release were almost entirely phosphorylcholine, indicating the activation of a phospholipase C specific for phosphatidylcholine. By comparison, 1 nM CCK8 stimulated [3H]ethanolamine metabolite release from [3H]ethanolamine-labeled acini by only 22% of control. These data suggest that CCK stimulates both phosphatidylinositol 4,5-bisphosphate and phosphatidylcholine hydrolysis; the latter may contribute to the sustained generation of DAG and hence the maintained activation of protein kinase C.

Human insulin receptor radioimmunoassay: applicability to insulin-resistant states

A radioimmunoassay of the human insulin receptor was developed employing a potent rabbit polyclonal antibody to the human insulin receptor and a highly purified human placental insulin receptor preparation. The receptor, obtained by sequential affinity chromatography with insulin receptor monoclonal antibody-agarose and wheat germ agglutinin-agarose, was radiolabeled with 125I-Bolton-Hunter reagent at specific activities of 2,100-3,300 Ci/mmol. Over 75% of this ligand was immunoprecipitable with the polyclonal antireceptor antibody and remained immunoprecipitable for greater than 45 days. The assay was sensitive to unlabeled receptor concentrations as low as 0.2 ng/0.5 ml; unlabeled insulin did not cross-react and unlabeled insulin-like growth factor (IGF)-I receptor cross-reacted weakly. The radioimmunoassay was applicable to the measurement of insulin receptors in tissues and cells that were extracted by solubilization in 1% Triton X-100; no purification of the extracted receptor was necessary. Of the three major target tissues for insulin action studied, liver had the highest concentration of receptors (47.6 ng/mg protein); fat and muscle had lower levels. Other studies with the radioimmunoassay indicated that insulin receptors were decreased both in monocytes from obese hyperinsulinemic subjects and in fibroblasts from patients with leprechaunism.

Increase in compressive strength of glass ionomer restorative materials with respect to time: a guide to their suitability for use in posterior primary dentition

Glass ionomer restorative cements have been used in anterior restorations for a number of years but have not been considered strong enough for use in posterior restorations. The compressive strengths of a number of materials currently available were measured at 30 min, 1 hour and 24 hours. It was concluded that some of the materials might be considered for posterior restorations in deciduous teeth where no other considerations, such as radiopacity, apply.

Femtosecond pulse generation from a titanium-doped sapphire laser using nonlinear external cavity feedback

A continuous-wave, argon-ion-pumped, titanium-doped sapphire laser has been constructed. Pulses of 80-psec duration obtained through active mode locking have been compressed to less than 800 fsec using nonlinear external cavity feedback.