Showing papers by "Université de Sherbrooke published in 1993"

Vortex-induced vibrations of a long flexible circular cylinder

Abstract: In an experimental study of the vortex-induced oscillations of a long flexible circular cylinder, the observed stationary amplitudes describe an hysteresis loop partially different from earlier studies. Each branch of the loop is associated with a vortex shedding mode and, as a jump from one branch to the other occurs, the phase difference between the cylinder displacement and the vortex shedding undergoes an abrupt change. The critical flow velocities at which the jump occurs concur with the flow visualization observations of Williamson & Roshko (1988) on the vortex shedding modes near the fundamental synchronization region. Impulsive regimes, obtained at a given flow velocity with the cylinder initially at rest or pre-excited, and progressive regimes resulting from a variation of the flow velocity, are examined. The occurrence of bifurcations is detected for a flow velocity range in the case of the impulsive regimes. The coordinates of the bifurcations define a boundary between two vortex shedding modes, a boundary that verifies the critical curve obtained by Williamson & Roshko (1988). The experimental set-up of this study simulates half the wavelength of a vibrating cable, eliminates the end effects present in oscillating rigid cylinder set-up and has one of the lowest damping ratios reported for the study of this phenomenon.

A Comparison of Management Patterns after Acute Myocardial Infarction in Canada and the United States

Abstract: Background There are major differences in the organization of the health care systems in Canada and the United States. We hypothesized that these differences may be accompanied by differences in patient care. Methods To test our hypothesis, we compared the treatment patterns for patients with acute myocardial infarction in 19 Canadian and 93 United States hospitals participating in the Survival and Ventricular Enlargement (SAVE) study, which tested the effectiveness of captopril in this population of patients after a myocardial infarction. Results In Canada, 51 percent of the patients admitted to a participating coronary care unit had acute myocardial infarctions, as compared with only 35 percent in the United States (P<0.001). Despite the similar clinical characteristics of the 1573 U.S. patients and 658 Canadian patients participating in the study, coronary arteriography was more commonly performed in the United States than in Canada (in 68 percent vs. 35 percent, P<0.001), as were revascularization pro...

The effect of improved glycemic control on cognitive functions in the elderly patient with diabetes.

Abstract: BACKGROUND A number of studies have found that cognitive function is impaired in elderly patients with non-insulin dependent diabetes mellitus (NIDDM) when compared with age-matched non-diabetic controls. In addition, it has been reported that elderly NIDDM patients who have poor glycemic control have a greater impairment in cognition that elderly NIDDM patients with good control. We conducted the following prospective study to determine if improved glycemic control would result in an improvement in cognitive function in elderly patients with NIDDM: METHODS Sixteen untreated elderly patients with NIDDM underwent a battery of neuropsychologic tests on two occasions, separated by at least two weeks. They were then started on an oral hypoglycemic agent. After they had been on a stable dose of medication for 6 months the neuropsychologic tests were repeated. RESULTS Fasting glucose decreased significantly after treatment (before: 13.8 +/- 1.2 mmol/l; after 8.4 +/- 0.4 mmol/l, p < .01). After 6 months of treatment patients had improvement in their scores on the Grooved Pegboard, Trail Making-Part A, Stroop-Word Naming, Cued Recall and Picture Arrangement tests (all p < .05). CONCLUSIONS Improved glycemic control in the elderly patient with NIDDM may have beneficial effects on selective areas of cognition.

Release of interleukin-8, interleukin-6, and colony-stimulating factors by upper airway epithelial cells: implications for cystic fibrosis.

Abstract: Cystic fibrosis (CF) is characterized by a dramatic neutrophil recruitment and repeated Pseudomonas infections in the lungs. To evaluate cytokine releasability by airway epithelial cells in the context of CF, we studied primary nasal epithelial cells isolated from the upper airways and continuous epithelial cell lines from normal and CF subjects. Relatively low levels of interleukin (IL)-8, IL-6, and granulocyte/macrophage colony-stimulating factor (GM-CSF) were produced spontaneously by primary epithelial cells (< 50 pg/106 cells) and higher levels of colony-stimulating factor-1 (CSF-1) (1 to 2 ng/106 cells). Cells were stimulated with substances that are likely to be present in the inflamed lungs of CF patients—namely, the proinflammatory monokines IL-1 and tumor necrosis factor-α (TNFα) as well as neutrophil elastase and bacterial products from Pseudomonas (mucoid exopolysaccharide [MEP] and rhamnolipids). Both IL-1 and TNFα induced a dose-dependent release of IL-6 (5 to 10 ng/106 cells) and GM-CSF (2 ...

Harmonic generation by the H 2 + molecular ion in intense laser fields

Abstract: The harmonic-generation (HG) spectra of the ${\mathrm{H}}_{2}^{+}$ molecular ion generated by short, intense, linearly polarized laser pulses are calculated nonperturbatively by solving a three-dimensional time-dependent Schr\"odinger equation. It is found that while ${\mathrm{H}}_{2}^{+}$ radiates in a similar manner to an atomic system such as H or ${\mathrm{He}}^{+}$ at high frequencies, the molecular ion in high-vibrational states or at large internuclear distances behaves analogously to a two-level system in an intense, relatively-long-wavelength laser field. It will be shown that symmetric molecular ions should in general produce more efficient harmonic generation than atoms, due to the presence of molecular charge-resonance (CR) states, which have no atomic analogues. Two HG plateaus, one molecular due to CR transitions and one atomiclike, appear for a long-wavelength excitation. Each plateau has its own maximum harmonic-number cutoff, which can be rationalized in terms of the maximum energy which can be acquired by an electron in the laser field.

Edge detection algorithms for two-dimensional ecological data

Abstract: The widely advocated statement that ecotone movement may be useful in studies of the impacts of global warming implies not only the ecotones exist but that they can be delineated spatially. With sampled field data, the accuracy of the detected ecotone is related to the data type and its spatiotemporal resolution. In the present study, I introduce two edge detection algorithms for regularly (lattice—wombling) and irregularly (triangulation—wombling) two—dimensional sampled data. I investigate the reliability of these algorithms in detecting potential ecotones using simulated vegetation data that follow the individualistic, continuum—gradient, and community—type patterns. Ecotones were defined quantitatively as long narrow regions of high rates of change. Under this definition, significant ecotones were found mostly in the community—type patterns using either of the edge detection algorithms (lattice—wombling or triangulation—wombling) and a systematic or random sampling design, respectively. See full-text ...

IL-10 neutralization augments mouse resistance to systemic Mycobacterium avium infections.

Abstract: In this contribution, we examined the involvement of the cytokine IL-10 in the progression of experimental murine Mycobacterium avium infections in susceptible BALB/c mice. Addition of anti-IL-10 antibodies in the supernatants of peritoneal macrophages infected with virulent M. avium resulted in a significantly enhanced mycobacteriostatic activity of macrophages. In BALB/c mice infected with the B101 or B102 virulent M. avium strains, examination of the cytokine release profile in splenocytes from infected mice showed that infection was associated with an initial copious release of both IFN-gamma and IL-10. IL-10 production increased as the infection progressed, whereas IFN-gamma levels diminished. Infected mice were given repeated infusions of a rat mAb against mouse IL-10 or rat IgM. Examination of IgM serum levels in anti-IL-10-treated mice (infected or not) showed that depletion of endogenous IL-10 resulted in much decreased IgM levels. Results showed that infusions of large dosages of the monoclonal anti-IL-10 resulted in a very significantly diminished bacterial growth in the spleens. These findings indicate that IL-10 may have a negative impact on resistance to M. avium infections, due, at least in part, to decreased macrophage activity.

Lepidopteran-specific crystal toxins from Bacillus thuringiensis form cation- and anion-selective channels in planar lipid bilayers.

Abstract: Previous studies in our laboratory have shown that CryIC, a lepidopteran-specific toxin from Bacillus thuringiensis, triggers calcium and chloride channel activity in SF-9 cells (Spodoptera frugiperda, fall armyworm). Chloride currents were also observed in SF-9 membrane patches upon addition of CryIC toxin to the cytoplasmic side of the membrane. In the present study the ability of activated CryIC toxin to form channels was investigated in a receptor-free, artificial phospholipid membrane system. We demonstrate that this toxin can partition in planar lipid bilayers and form ion-selective channels with a large range of conductances. These channels display complex activity patterns, often possess subconducting states and are selective to either anions or cations. These properties appeared to be pH dependent. At pH 9.5, cation-selective channels of 100 to 200 pS were most frequently observed. Among the channels recorded at pH 6.0, a 25-35 pS anion-selective channel was often seen at pH 6.0, with permeation and kinetic properties similar to those of the channels previously observed in cultured lepidopteran cells under comparable pH environment and for the same CryIC toxin doses. We conclude that insertion of CryIC toxin in SF-9 cell native membranes and in artificial planar phospholipid bilayers may result from an identical lipid-protein interaction mechanism.

Hydrogen evolution reaction on Ni-Al electrodes

Abstract: The hydrogen evolution reaction (h.e.r) was studied in alkaline solutions on two types of electrodes: (1) obtained by alloying Raney nickel without or with nickel and (ii) by pressing Raney nickel and nickel powders at room temperature. The obtained electrodes are usually very active for the h.e.r. The most active electrode was obtained by pressing Raney nickel with nickel powder (50 wt %). It was characterized by a large roughness factor, R ∼ 10 000 and a very low overpotential at the current density of 250 mA cm−2, η250 = 56 mV. The mechanism of the h.e.r. was studied using a.c. impedance measurements. The high electrode activity is connected with the increase in the intrinsic activity of the porous electrode surface.

Receptors for bradykinin and related kinins: a critical analysis.

Abstract: Kinins exert a variety of biological actions and have been implicated in the pathogenesis of inflammation, pain, asthma, and other diseases. Kinins act through specific receptors that are widespread and belong to two major categories, B1 and B2. B2 has been cloned and shown to be of the rhodopsin type, consisting of seven hydrophobic membrane domains connected by extracellular and intracellular loops. Recent pharmacological findings from various laboratories suggest the existence of new receptor types, which have been named B3, B4, and B5. These findings are analysed critically, especially with respect to the criteria that have been used for affirming the existence of new receptor entities. The analysis is restricted to data obtained in isolated organs, almost exclusively smooth muscle preparations. Criteria for receptor characterization and classification are the order of potency of agonists and the apparent affinities of antagonists. The analysis reveals that receptors for bradykinin and related kinins are of two types, B1 and B2. B1 mediates the rapid acute response (smooth muscle contraction or relaxation) as well as some effects occurring more slowly (e.g., collagen synthesis). B1 receptor functions have been shown to be modulated by interleukins. B2 receptors are responsible for most of the kinins' biological effects, including arterial vasodilatation, plasma extravasation, venoconstriction, activation of sensory fibers (e.g., fibers for pain), and stimulation of the release of prostaglandins, endothelium-dependent relaxing factor (from endothelia), noradrenaline (from nerve terminals and adrenals), and other endogenous agents. The pharmacological characteristics of the receptor sites (B2) mediating this array of biological effects show differences between species, and two B2 receptor subtypes are proposed, namely B2A (rabbit, dog, and possibly man) and B2B (guinea pig, hamster, rat). B2A and B2B receptor subtypes have been characterized by using fairly selective agonists and competitive antagonists (e.g., D-Arg[Hyp3, D-Phe7,Leu8]BK). Noncompetitive antagonists (non-equilibrium), such as HOE 140, do not discriminate between B2A and B2B subtypes. Species differences cannot account for the multiplicity of receptors that have been proposed for rat vas deferens, pre- and post-junctional sites, and rat uterus, guinea pig ileum, and rat blood pressure. The existence of hypothetical new receptor sites was based on data obtained with partial agonists and have not been substantiated by data obtained with potent pure antagonists. The B3 receptor, proposed to explain the unusual behaviour of the guinea pig tracheal response to kinins, has to be carefully reconsidered after the finding that HOE 140 acts as a pure antagonist on this tissue and shows a fairly high affinity for the tracheal site.(ABSTRACT TRUNCATED AT 400 WORDS)

Some effects of chitosan on liver function in the rat.

Abstract: Chitosan, a natural product derived from chitin, possesses hypocholesterolemic properties similar to those of cholestyramine, but there has been no report concerning its effects on the equilibrium between dietary cholesterol and de novo cholesterol synthesis in the liver. In this work, we studied the effects of chitosan on plasma and liver cholesterol levels, liver weight, and the key regulatory enzyme of cholesterogenesis 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase in rats fed a sterol diet containing 1% cholesterol and 0.2% cholic acid. The animals given the sterol diet showed increases in plasma and liver cholesterol, which were lowered by 54% in plasma and 64% in liver by 5% chitosan, while cholestyramine completely blocked such increases. HMG-CoA reductase activity was considerably increased in the sterol-cholestyramine group, but was greatly decreased in both sterol and sterol-chitosan groups. There was no change in liver weight or appearance after treatment with chitosan, but cholestyramine-treated animals manifested secondary effects from the treatment, including smaller yellowish livers. High mol wt chitosans [> 750 kilodaltons (kDa)] were found to be less effective as hypocholesterolemia than a 70-kDa preparation. Also, when the 70-kDa chitosan was used at 2.5%, 5%, and 7.5% of the total diet, its effectiveness was greatest at the higher concentrations; indeed, incorporation of 7.5% chitosan in the sterol diet for 3 weeks completely prevented any decrease in plasma high density lipoprotein cholesterol or increase in the plasma cholesterol level and liver weight. This formula greatly reduced the increase in liver cholesterol content due to the sterol diet, with values of 8.8 +/- 1.3 for the sterol-chitosan diet vs. 18.2 +/- 0.8 mg/g tissue for the sterol diet. The increased intake of sterols considerably lowered both HMG-CoA reductase activity (33-fold) and HMG-CoA reductase mRNA levels (3-fold) in rat liver, but in the sterol-chitosan group, HMG-CoA reductase activity was 7.7 times more elevated than in the sterol group, although it was still lower than the control value, whereas HMG-CoA reductase mRNA levels were normal. The results obtained did not differ significantly when rats were studied for 1, 3, or 6 weeks. These results taken collectively indicate that the 7.5% chitosan formula maintained adequate cholesterol homeostasis in rats, despite a greatly increased intake of cholesterol.

Molecular stabilization and angular distribution in photodissociation of H2+ in intense laser fields

Abstract: Photodissociation probabilities of the H[sub 2][sup +] molecule calculated from numerical solutions of the time-dependent Schroedinger equation exhibit minima for high-intensity (10[sup 12][lt][ital I][lt]10[sup 14] W/cm[sup 2]) subpicosecond (100 fs) laser-pulse excitation. These minima are shown to correspond to stabilization of the molecular ion and hence to suppression of the photodissociation by the creation of stable laser-induced resonances by a laser-induced avoided-crossing mechanism between the field-molecule potentials. Rotational excitations are shown to destroy such stabilization at intensities above 10[sup 13] W/cm[sup 2]. Angular distributions of the photofragments demonstrate gradual molecular alignment with increasing intensity. Bimodal distributions can also occur and they are the signature of the stabilization mechanism.

Pullout and bond of glass-fibre rods embedded in concrete and cement grout

Abstract: Consideration is being given to replacing steel rebars with glass-fibre rods in some specific areas, particularly those in which premature failure due to corrosion has been observed. This paper presents the results of an experimental study of pullout behaviour and bond characteristics of glass-fibre rods embedded in normal and high-strength concretes and in cement grout. The results of the study show that glass-fibre rod bond strength is about 12 MPa and the optimal anchored length approximately 10 times the rod diameter. The average modification factor of top-cast reinforcement was found to be equal to 1.23 and 1.18 for normal and high-strength concrete, respectively. Other considerations, such as bond slip, are also discussed in the paper. Comparisons with steel reinforcement are made whenever appropriate.

Nitric oxide modulates vascular permeability in the rat coronary circulation

Abstract: 1. The objective of the present study was to assess whether inhibition of nitric oxide (NO) production could modulate vascular permeability in the coronary circulation in conscious rats. 2. Intravenous injection of NG-nitro-L-arginine methyl ester (L-NAME, 2 mg kg-1) resulted in a slowly developing hypertension and evoked twofold increases in vascular permeability in the left ventricle and right atrium as measured by the extravasation of Evans blue dye. Maintenance of mean arterial blood pressure at the level observed following L-NAME injection by infusion of noradrenaline (620-820 ng kg-1 min-1) did not induce significant protein extravasation in the coronary circulation. 3. L-NAME treatment markedly enhanced (up to 490%) protein extravasation both in the left ventricle and right atrium in response to platelet-activating factor (PAF, 1.9 nmol kg-1, i.v.) and endothelin-1 (1 nmol kg-1, i.v.). Noradrenaline infusion potentiated (up to 69%) endothelin-1-induced protein extravasation. The permeability effect of PAF was only slightly enhanced by noradrenaline. 4. The present findings indicate that inhibition of endogenous NO synthesis leads to an increase in protein extravasation and to potentiation of the permeability effects of PAF and endothelin-1 in the coronary circulation. These results also suggest that NO may be an important regulator of vascular permeability under physiological and pathological conditions.

Electronic aging and related electron interactions in thin-film dielectrics

Abstract: The author points out that hot electrons generated in dielectrics subjected to high electrical field strengths can produce highly reactive chemical species which contribute to the aging process. The study of the interaction of such low energy (0 to 15 eV) electrons near the surface of dielectrics in experiments combining cryogenic thin film deposition and high-resolution low-energy electron-beam techniques is discussed. Examples of the results obtained with thin film atomic and molecular solids are used to illustrate the basic mechanisms which control the electron-dielectric interactions and provide a description of the basic degradation processes involved during electronic aging. It is shown that elastic and quasi-elastic scattering of hot electrons in dielectrics can be described in terms of band structure parameters, whereas inelastic scattering is often governed by the formation of transient anions. These anions can decay by stabilization, by producing vibrationally and electronically excited molecules, or by dissociating into a stable anion and a neutral radical. These latter species usually initiate other reactions with nearby molecules, causing further chemical damage. >

Effect of dysfunctional vascular endothelium on myocardial performance in isolated papillary muscles.

Abstract: Vascular endothelium has been shown to modify the contractile characteristics of vascular smooth muscle, and endocardial endothelium has been shown to modify the contractile characteristics of adjacent myocardium. In this study, whether vascular endothelium also modifies the contractile characteristics of adjacent myocardium and whether these effects are additive to those of endocardial endothelium were investigated. Rabbit hearts (n = 54) were excised and mounted in a Langendorff preparation. Vascular reactivity was verified by acetylcholine infusion. One group of these hearts had Triton X-100 injected as a bolus into the coronaries to render the vascular endothelium dysfunctional. The other portion served as control hearts. Triton X-100 bolus injection resulted in little or no pathological changes on morphological examination; however, the vasodilatory response to acetylcholine in these hearts was abolished, suggesting vascular endothelial dysfunction. Vascular smooth muscle reactivity was verified in Triton X-100-injected hearts by nitroprusside infusion. In the control Langendorff-perfused hearts, there was little evidence of vascular endothelial dysfunction, with the coronary perfusion rate increasing from 8.9 +/- 0.4 to 11.0 +/- 0.3 ml/g per minute (p < 0.01) in response to acetylcholine. All hearts were then removed, and right ventricular papillary muscles were excised for myocardial mechanical studies. Control Langendorff-perfused hearts had myocardial mechanical characteristics similar to those of muscles from 18 other control hearts without Langendorff perfusion, indicating that the Langendorff perfusion itself had little effect on myocardial mechanics. The muscles from the Triton X-100-injected Langendorff hearts had marked changes: a shortening of twitch duration (363 +/- 16 versus 449 +/- 9 msec, p < 0.01) and decreases in total tension (2.2 +/- 0.2 versus 2.9 +/- 0.2 g/mm2, p < 0.01), dT/dt (9 +/- 1 versus 12 +/- 1 g/mm2 per second, p < 0.05), and maximum velocity of unloaded muscle shortening (Vmax) (0.89 +/- 0.06 versus 1.14 +/- 0.07 length at which maximum developed tension occurred [Lmax]/sec, p < 0.05). Endocardial endothelial removal of the papillary muscles in the two control groups (with and without Langendorff perfusion) by Triton X-100 caused the same changes in twitch characteristics as occurred in muscles from the Langendorff-perfused hearts injected with Triton X-100 but with intact endocardial endothelium, suggesting that vascular endothelial dysfunction had similar effects on contractile characteristics as endocardial endothelial removal.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement by endothelin-1 of microvascular permeability via the activation of ETA receptors.

Abstract: 1. The objective of the present experiments was to assess the involvement of endothelin-A (ETA) receptors in mediating the effects of endothelin-1 on microvascular permeability in conscious rats. 2. Bolus injection of endothelin-1 (0.1 and 1 nmol kg-1, i.v.) resulted in a dose-dependent prolonged pressor effect preceded by a transient depressor response. These changes were accompanied by a dose-dependent loss of plasma volume. Endothelin-1 (1 nmol kg-1) enhanced the vascular permeability of the upper and lower bronchi, kidney, stomach, duodenum and spleen (up to 270%) as measured by the extravasation of Evans blue dye. 3. Pretreatment of the animals with the selective ETA receptor antagonist, BQ-123 (1 mg kg-1, i.v.) significantly blunted the pressor response to endothelin-1 without affecting the depressor response. BQ-123 inhibited by 87% the endothelin-1 (1 nmol kg-1)-induced plasma volume loss. BQ-123 markedly attenuated protein extravasation elicited by endothelin-1 in the upper and lower bronchi and kidney, whereas it completely inhibited the permeability effect of endothelin-1 in the stomach and duodenum. BQ-123 by itself had no significant effect on the parameters studied. 4. The endothelin-1 analogue, [Trp(For)21]-endothelin-1, in which Trp21 is formylated, was as potent a pressor agent as endothelin-1, but had no depressor action. Bolus injection of [Trp(For)21]-endothelin-1 (0.1 and 1 nmol kg-1, i.v.) evoked similar plasma volume losses to those observed following administration of equimolar doses of endothelin-1. Furthermore, 1 nmol kg-1 [Trp(For)21]-endothelin-l evoked increases in protein extravasation similar to endothelin-l, 1 nmol kg-1.5. The present findings suggest that endothelin- 1 enhances microvascular permeability, in part, via the activation of ETA receptors.

Efficacy of ticlopidine and aspirin for prevention of reversible cerebrovascular ischemic events. The Ticlopidine Aspirin Stroke Study.

Abstract: This subgroup analysis from the Ticlopidine Aspirin Stroke Study (TASS) compared ticlopidine, a new antiplatelet agent, with aspirin for the prevention of recurrent transient ischemic attacks in pa

Vascular responses to endothelin-1 following inhibition of nitric oxide synthesis in the conscious rat.

Abstract: 1. The objectives of the present experiments were to assess the role of endogenous nitric oxide (NO) in mediating and/or modulating the effects of endothelin-1 (ET-1) on blood pressure and microvascular permeability in conscious rats. 2. Intravenous administration of the NO synthesis inhibitors, NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine methyl ester (L-NAME) at a dose (25 mg kg-1 or 2 mg kg-1, respectively) which evoked maximum increase in mean arterial blood pressure (MABP) significantly attenuated (by about 40%) the vasodepressor response and potentiated (by 100-180%) the pressor response to ET-1 (1 nmol kg-1, i.v.) compared to the effects of ET-1 in animals where the peripheral vasoconstrictor effects of L-arginine analogues were mimicked by an infusion of noradrenaline (620-820 ng kg-1 min-1). Similar inhibition of the depressor and potentiation of the pressor actions of ET-1 were observed when the MABP which had been elevated by L-NMMA or L-NAME was titrated to normotensive levels with hydralazine or diazoxide before injection of ET-1. 3. L-NAME (2 mg kg-1) increased the vascular permeability of the large airways, stomach, duodenum, pancreas, liver, kidney and spleen (up to 280%) as measured by the extravasation of Evans blue dye. The permeability of pulmonary parenchyma, skeletal muscle and skin was not affected significantly by L-NAME treatment. Elevation of MABP by noradrenaline infusion did not evoke protein extravasation in the vascular beds studied with the exception of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Reconstitution in vitro of the pH-dependent aggregation of pancreatic zymogens en route to the secretory granule: implication of GP-2.

Abstract: Regulated secretory proteins are thought to be sorted in the trans-Golgi network (TGN) via selective aggregation. To elucidate the biogenesis of the secretory granule in the exocrine pancreas, we reconstituted in vitro the conditions of pH and ions believed to exist in the TGN using the end product of this sorting process, the zymogen granule contents. Protein aggregation was dependent on pH (acidic) and on the presence of cations (10 mM Ca2+, 150 mM K+) to reproduce the pattern of proteins found in the granule. The constitutive secretory protein IgG was excluded from these aggregates. Zymogen aggregation correlated with the relative proportion of the major granule membrane protein GP-2 in the assay. These results show that the glycosylphosphatidylinositol-anchored protein GP-2 co-aggregates with zymogens in the acidic environment believed to exist in the pancreatic TGN, and thus suggest that GP-2 would function as a membrane anchor for zymogen aggregates, facilitating their entrapment in budding vesicles directed towards the regulated secretory pathway.