Synthesis, intracellular transport and discharge of exportable proteins in the pancreatic acinar cell and other cells

Intracellular transport and storage of secretory proteins in relation to cytodifferentiation in neoplastic pancreatic acinar cells

The pancreatic acinar carcinoma established in rat by Reddy and Rao (1977, Science 198:78-80) demonstrates heterogeneity of cytodifferentiation ranging from cells containing abundant well-developed secretory granules to those with virtually none. We examined the synthesis intracellular transport and storage of secretory proteins in secretory granule-enriched (GEF) and secretory granule-deficient (GDF) subpopulations of neoplastic acinar cells separable by Percoll gradient centrifugation, to determine the secretory process in cells with distinctly different cytodifferentiation. The cells pulse-labeled with [3H]leucine for 3 min and chase incubated for up to 4 h were analyzed by quantitative electron microscope autoradiography. In GEF neoplastic cells, the results of grain counts and relative grain density estimates establish that the label moves successively from rough endoplasmic reticulum (RER) leads to the Golgi apparatus leads to post-Golgi vesicles (vacuoles or immature granules) leads to mature secretory granules, in a manner reminiscent of the secretory process in normal pancreatic acinar cells. The presence of approximately 40% of the label in association with secretory granules at 4 h postpulse indicates that GEF neoplastic cells retain (acquire) the essential regulatory controls of the secretory process. In GDF neoplastic acinar cells the drainage of label from RER is slower, but the peak label of approximately 20% in the Golgi apparatus is reached relatively rapidly (10 min postpulse). The movement of label from the Golgi to the post-Golgi vesicles is evident; further delineation of the secretory process in GDF neoplastic cells, however, was not possible due to lack of secretory granule differentiation. The movement of label from RER leads to the Golgi apparatus leads to the post-Golgi vesicles suggests that GDF neoplastic cells also synthesize secretory proteins, but to a lesser extent than the GEF cells. The reason(s) for the inability of GDF cells to concentrate and store exportable proteins remain to be elucidated.

Direct demonstration of increases in cytosolic free Ca2+ during stimulation of pancreatic enzyme secretion

The Ca2+-activated photoprotein aequorin has been incorporated into intact, isolated rat pancreatic acini by a hypotonic swelling method. The isolated acini retained normal secretory responses after loading with aequorin. Increases in cytosolic Ca2+ concentration in response to a physiological secretagogue, carbamylcholine, and to divalent-cation ionophore A23187 have been demonstrated. Simultaneous measurement of the dynamics of enzyme secretion and changes in cytosolic Ca2+ concentration has been achieved using a newly developed apparatus.

Receptors for insulin and CCK in the acinar pancreas: relationship to hormone action

These studies, therefore, allow a model of how CCK and insulin regulate the acinar pancreas in a coordinated manner (Fig. 27). CCK, after its secretion by gut cells, interacts with a specific receptor on the cell surface and then increases intracellular free Ca2+. Ca2+, in turn (1) interacts with the secretory granules leading to zymogen release, (2) stimulates protein synthesis, and (3) increases glucose transport. The model is supported on the finding of specific high affinity CCK receptors on acini and by the localization of CCK to the plasma membrane in EM autoradiographs. Insulin, secreted from the pancreatic islets, also interacts with a specific receptor on the cell surface. Either via a messenger generated by this reaction, or via insulin's subsequent direct interaction with intracellular organelles, such as the Golgi-endoplasmic reticulum, protein synthesis is initiated and glucose transport is increased. Then a series of events is initiated to increase cell growth, amylase content, and sensitivity to CCK. These studies, therefore, indicate that the control of acinar cell function is a product of cooperative intrahormonal interactions.

Discrete changes of cell membrane capacitance observed under conditions of enhanced secretion in bovine adrenal chromaffin cells

The capacitance of the surface membrane of small adrenal chromaffin cells was measured with patch-clamp pipettes. Continuous and discrete changes of capacitance were observed. They were interpreted as changes of surface area connected to exocytotic or endocytotic processes. Most of the measurements were performed in the "whole-cell" recording configuration [Hamill, O. P., Marty, A., Neher, E., Sakmann, B. & Sigworth, F. J. (1981) Pflügers Arch. 391, 85-100], which allows the intracellular Ca2+ concentration to be controlled. With an internal solution highly buffered to low values of Ca2+ concentration (10 nM), the surface capacitance usually decreased and could not be markedly changed by electrical stimulation. At low buffering capacity and medium Ca2+ concentrations (0.1-1 microM), the capacitance measurement showed large fluctuations and discrete steps, reflecting both capacitance decrease and increase. A large transient increase of capacitance could be induced by electrical stimulation under these conditions. It was linked to Ca2+ currents through the membrane. Relatively large (2-6 x 10(-14) F) steps of capacitance decrease were common after extensive stimulation. The size distribution of step-like capacitance changes is well compatible with the idea that steps of capacitance increase reflect individual events of exocytosis of chromaffin granules, whereas steps of the opposite polarity reflect the formation of vesicles or vacuoles by endocytosis.

Unidirectional uptake of L-alanine and L-serine by system ASC in the basolateral membrane of cat salivary epithelium. Selective inhibition of rapid alanine metabolism by aminooxyacetate

Unidirectional influx of L-alanine and L-serine across the basolateral membrane of cat salivary epithelium was investigated in perfused submandibular glands using a rapid (less than 30 s) paired-tracer dilution technique. (Bustamante, J.C., Mann, G.E. and Yudilevich, D.L. (1981) J. Physiol. 313, 65-79). High uptakes were measured for both neutral amino acids, however, only the uptake of L-alanine was followed by an immediate tracer efflux into the circulation. Aminooxyacetate, an inhibitor of alanine aminotransferase, completely inhibited this efflux and glandular pyruvate production. These results demonstrate that in assessing unidirectional amino acid uptake, the influence of metabolism should be considered even during short intervals of measurement.

Role of cyclic adenosine monophosphate in amylase release from dissociated rat pancreatic acini

1. The effect of octapeptide of cholecystokinin-pancreozymin (CCK(8)), bethanechol, cholera toxin, glucagon and vasoactive intestinal polypeptide (VIP) on amylase secretion and lactic dehydrogenase (LDH) release from isolated rat pancreatic acini was studied.2. In isolated rat pancreatic acini, in the absence of theophylline in the medium, amylase secretion was increased by 65-78% with 10(-7) and 10(-6) M-cholera toxin. In the presence of theophylline, amylase secretion was increased by 43-56% with 10(-7) and 10(-6) M-cholera toxin following a 90 min incubation. No effect was observed in the presence of theophylline at 30 and 60 min. The effect of cholera toxin was potentiated by CCK(8) at 60 and 90 min.3. In the absence of theophylline in the medium, amylase secretion was increased by 81-118% with 10(-5) and 10(-4) M-glucagon and 86% with 10(-6) M-VIP at 60 min. In the presence of theophylline in the medium, amylase secretion was increased by 53-246% with 10(-9) to 10(-6) M-glucagon and 111-158% with 10(-7) and 10(-6) M-VIP respectively. The effect of glucagon and VIP was potentiated by CCK(8).4. Potentiation of the rate of amylase release due to glucagon (10(-5) M) and VIP (10(-6) M) occurred during the first 15 min of incubation.5. Release of LDH was not increased by any of these agents.6. It is concluded that cyclic AMP rise (due to cholera toxin, glucagon and VIP effect) increased amylase secretion from rat pancreatic acinar cells. This effect is less marked than in the guinea-pig pancreas and is potentiated by agents mobilizing cellular Ca(2+) (CCK(8) and bethanechol).7. These data indicate species-specific variation in the action of cyclic AMP in the pancreas.

Newly synthesized secretory proteins from pig pancreas are not released from a homogeneous granule compartment

The pancreatic secretion of anesthetized pigs was collected by cannulation after pulse labeling with [3H]leucine. Collection at 5 min intervals started immediately post-pulse labeling up to 85 min. The volume, the protein content and the trichloroacetic acid-precipitable radioactivity of the juice were measured. The specific radioactivity of the secretory proteins was compared to that of a zymogen granule fraction isolated from the same animal. The latter was very much higher. Caerulein stimulation for 5 min at 80 min post-pulse caused a sharp drop in the specific activity of secretory proteins in the juice, to a level lower than that of the zymogen granule content. These data support the concept of more than one pool of secretory proteins in the pancreas and are incompatible with the concept that secretory proteins derive from an homogeneous granule compartment in a functionally homogeneous population of cells. To explain our results the hypothesis of a second intracellular route for the secretory proteins in proposed.

Perikaryal routing of newly synthesized proteins in regenerating neurons: quantitative electron microscopic autoradiography

Intracellular transport of newly synthesized proteins through organelles in the perikarya of regenerating goldfish retinal ganglion cells was studied using electron microscopic autoradiography. Retinas were removed 14 or 30 days after optic tract cut or sham operation, pulse-labeled in [3H]proline-containing medium for 5 min, and then chase-incubated in medium containing unlabeled proline for various times up to 55 min before fixation. Fourteen days after axotomy, during rapid growth of the regenerating axons, the time course of change of relative grain density (% grains/% area) in the rough endoplasmic reticulum in regenerating cells was almost identical to that in control cells. However, the grain distribution analysis revealed an increased delivery of newly synthesized proteins to the Golgi apparatus, perikaryal plasma membrane and nucleus in regenerating cells. Thirty days after axotomy, during synaptogenesis, Golgi apparatus labeling in the regenerating cells became significantly higher than control, but the increase was delayed compared to the increase seen 14 days after axotomy. Labeling of the plasma membrane and nucleus did not rise above control in 30-day regenerating cells chase-incubated for up to 55 min. Thus the pattern of intracellular transport of newly synthesized proteins varies with the stage stage of axonal regeneration.

The effect of atropine and duct decompression on the evolution of Diazinon-induced acute canine pancreatitis

Three groups of eight dogs each were studied to evaluate the early evolution of the hyperamylasemia, hyperlipasemia, and acinar cell pathology at the light and electron microscopic levels during acute Diazinon-induced pancreatitis. Two more groups of five dogs each were evaluated for the effects of cholinergic receptor blockade with atropine and ductal decompression on the evolution of serum enzyme changes and acinar cell pathology. Group I dogs received a secretin infusion of 2 units/kg/hr, and a Diazinon infusion of 75 mg/kg, and demonstrated significant increases in serum amylase and lipase at one, two and three hours. Light microscopy revealed acinar cell vacuolization and progressive interstitial edema. Electron microscopy revealed the formation of large intracytoplasmic vacuoles filled with flocculent material, the fusion of these vacuoles with basolateral membrane, and the formation of interstitial edema. In both group II dogs (that received secretin alone) and Group III dogs (that received atropine, 200 micrograms/kg IV prior to secretin and Diazinon), the serum enzyme levels and histologic results were normal. In group IV dogs, pancreatic duct cannulation to prevent hypertension prevented the hyperamylasemia and hyperlipasemia, but not the acinar cell vacuolization and interstitial edema. This model for acute interstitial pancreatitis is apparently cholinergic-receptor mediated, the serum enzyme elevations are due primarily to ductal hypertension, and the acinar cell pathology is primarily due to cholinergic stimulation and occurs independent of ductal hypertension.

Transport of newly synthesized proteins into mitochondria - a review

This review examines the mechanism of translocation of cytoplasmically synthesized proteins into mitochondria. Approximately 10% of the mitochondrial proteins are synthesized within the organelles while most mitochondrial proteins are coded for by nuclear genes and synthesized on cytoplasmic ribosomes. Those mitochondrial proteins synthesized on cytoplasmic ribosomes have to be transferred at some point into one of the mitochondrial compartments, a process which would require their insertion through one or both mitochondrial membranes. Data accumulated during the past five years indicate that the cytoplasmically synthesized mitochondrial proteins are synthesized on free polysomes then released into the cytoplasm. Most of the proteins examined so far are synthesized in the cytoplasm as larger precursors whose conformations may differ from the conformations of their respective mature forms. These precursor proteins become translocated into mitochondrial post-translationally and processed to their mature forms either during or immediately following translocation into the organelles. The translocation step appears to require mitochondrial ATP. Some processing activities have been localized in the matrix fractions of mitochondria from liver and yeast and they appear to be associated with soluble endopeptidases which act selectively on precursors of mitochondrial proteins. Although it is not clear how the precursor proteins interact with or recognize mitochondrial membranes, studies in yeast indicate that the interactions occur at specific regions on the other mitochondrial membranes.

The effect of extracellular calcium deprivation on amylase secretion and 45Ca efflux from rat pancreas

1. The role of extracellular Ca(2+) in pancreatic enzyme secretion and (45)Ca efflux evoked by acetylcholine (ACh) and caerulein has been assessed in the incubated, uncinate pancreas of young rats.2. In a medium containing 2.5 x 10(-3)m-Ca(2+), the maximal rates of amylase secretion evoked by optimal doses of each secretagogue were similar. However, the time courses of amylase release during prolonged stimulation of the gland were different.3. The time course of amylase secretion in response to an optimal dose of ACh (10(-5)m) was characterized by an initial rapid increase followed by a slow sustained rise. For caerulein (10(-8)m), an initial rapid rise was followed either by a plateau or slight decline in the rate of amylase secretion.4. Both secretagogues produced similar increases in the rate coefficient of (45)Ca efflux from the gland.5. With supra-optimal doses of the secretagogues, amylase secretion, but not the rate coefficient of (45)Ca efflux, was depressed.6. Reducing the extracellular Ca(2+) concentration did not have a marked effect on basal amylase secretion but inhibited the action of both secretagogues. When the Ca(2+) concentration was 10(-6)m or lower, these inhibitory effects were irreversible. Amylase secretion stimulated by ACh was more sensitive to extracellular Ca(2+) deprivation than that stimulated by caerulein, the concentration required for half-maximal secretion being about 9-fold greater for ACh.7. Decreasing the extracellular Ca(2+) concentration increased both the basal and stimulated rate coefficients of (45)Ca efflux.8. Our results support the hypothesis that pancreatic enzyme secretagogues act by releasing bound Ca(2+) from sites within the acinar cell. Furthermore, they suggest that the site utilized by ACh is more amenable to depletion, via changes in extracellular Ca(2+) concentration, than that employed by caerulein.

Pancreatic acinar cell function: measurement of intracellular ions and pH and their relation to secretion

1. Isolated mouse pancreatic acini were used to investigate the effect of secretagogues on acinar cellular electrolytes and cell pH. The effect of changes in the acid-base status of the incubation medium on acinar cellular electrolytes, cell pH and amylase release were also studied. 2. Carbachol at concentrations of 10(-6) or 10(-5) M was without any effect on the intracellular concentrations of total Na+, Na+ exchangeable with 22Na+, K+ and Cl-, and did not influence cell pH as determined by the DMO method. 3. Changes in pHe achieved by varying the HCO3- concentrations at constant CO2, varying the CO2 concentration at constant HCO3- or by titration of a HCO3-/CO2 free HEPES buffered medium did not influence intracellular electrolyte values. 4. pHi changed linearly with pHe by about 1.2 units/pHe unit change over the pHe range of 7.7--6.5. pHi, however, did not change in response to a change in the CO2 tension when the HCO3- concentration was adjusted to keep pHe at 7.4. 5. Lowering pHe below 7.1 inhibited carbachol and CCK8-stimulated amylase release. By contrast a decrease of pHe to 6.8 was without significant effect on basal and secretagogue increased 45Ca2+ efflux from pancreatic acini. 6. In conclusion the pH sensitivity of amylase release by acinar cells is probably related to changes in pHi. Since Ca2+ mobilization is not affected, the pH sensitive step is probably in the mechanism by which Ca2+ activates the release of zymogen granules contents by exocytosis.

The relationship between extracellular amino acids and protein synthesis is altered during axonal regeneration

The incorporation of [3H]proline into proteins of goldfish retinal ganglion cells was measured by light microscopic autoradiography of isolated retinas that had been incubated in labeled medium under pulse-chase conditions. It was found that the composition of the immediate precursor pool for protein synthesis is more directly influenced by extracellular amino acids in regenerating cells 14 d after axotomy than in sham-operated controls.

parallel secretion of secretory proteins and calcium by the rat parotid gland

1. The secretion of amylase, deoxyribonuclease, ribonuclease, protein and Ca2+ by the rat parotid gland in vitro was studied. 2. Isoproterenol and carbamoylcholine elicited a parallel discharge of amylase, deoxyribonuclease, ribonuclease and protein over a 40 min time period. 3. The composition of the secretion was independent of the secretogogue used for stimulation. When gland slices from the same animal were stimulated with isoproterenol, adrenaline, phenylephrine or carbamoylcholine, secretory enzymes and protein were secreted in constant proportions. 4. 45Ca injected intraperitoneally 16 h before stimulation with either isoproterenol or carbamoylcholine was released in parallel with amylase and protein. 5. The relative proportions of amylase, ribonuclease, deoxyribonuclease, protein and Ca present in isolated parotid gland secretory granules was identical to that of isoproterenol stimulated gland secretion. 6. It is concluded that the secretory proteins and Ca2+ are discharged in constant proportions by the rat parotid gland regardless of the mode of stimulation or the rate of secretion. The similarity in the composition of gland secretion and granule contents also suggests that enzymes and Ca2+ are released by exocytosis and not by diffusion across the apical plasma membrane.

The influence of topology and glycosylation on the fate of heterologous secretory proteins made in Xenopus oocytes

Secretory proteins made in Xenopus laevis oocytes under the direction of heterologous messenger RNA are modified, topologically segregated and exported. Thus the oocyte may serve as a useful surrogate secretory system and we have studied some of the factors governing access to the export pathway. Unglycosylated chicken ovalbumin, synthesized and trapped in the cytosol, is not secreted but glycosylated ovalbumin, found sequestered within vesicles, is exported from oocytes. However, ovalbumin, which is transferred across the endoplasmic reticulum in the presence of tunicamycin and which is indistinguishable by immunoprecipitation, by two-dimensional gel electrophoresis and by concanavalin-A--Sepharose binding from the cytosolic form, is still secreted. Guinea-pig milk proteins and human interferon are also exported from tunicamycin-treated frog cells. These observations demonstrate that access to the endoplasmic reticulum but not glycosylation is a mandatory intermediate step in secretion, and emphasize the advantages of the oocyte as a surrogate system for the study of the later events in the gene expression pathway.

Mouse uterine glands during the peri-implantation period. II. Autoradiographic studies

Protein synthesis and secretion in mouse uterine glands during the peri-implantation period were studied, by both light and electron microscopic autoradiography, after the in vivo administration of tritiated leucine (3H-leucine) and proline (3H-proline). Light microscopic autoradiography revealed that the time course of synthesis and secretion of labeled proteins was constant during days four, five, and six of pregnancy. Labeled material could be detected in the glandular lumen by 45 minutes after administration and in higher concentrations by 90 minutes after administration. Analysis of electron microscopic autoradiographs from days five and six of pregnancy showed that high levels of activity were initially present over the rough endoplasmic reticulum and Golgi complexes and subsequently declined at the longer time intervals (45 and 90 minutes), while activity over the glandular lumen increased with time. The pathway of intracellular transport to the glandular lumen appeared to be via small cytoplasmic vesicles on both days five and six of pregnancy. Additional pathways for transport of the labeled protein to the glandular lumen appeared to be present in the form of the large vesicles on day five and granules on day six of pregnancy. Throughout the peri-implantation period, mouse uterine glands were active secretory structures in which the mode of secretion was similar to other exocrine cells. Thus, the uterine glands of the mouse must be considered a source of uterine fluid proteins at the time of implantation that may contribute to quantitative changes in these proteins.

Amylase release from dissociated mouse pancreatic acinar cells stimulated by glucagon: effect of membrane stabilizers

1. The effect of membrane stabilizers and cytochalasin-B on amylase secretion, basal and induced by ionophore A23187, CCK-PZ, bethanechol and glucagon, was studied in dissociated mouse pancreatic acinar cells. 2. Cytochalasin-B did not affect basal or secretagogue-stimulated amylase secretion. 3. Membrane stabilizers [thymol (10(-7)-10(-4) M), chlorpromazine (10(-7)-10(-4) M) and propranolol (10(-7)-10(-5) M) did not alter basal release of amylase. At higher concentrations of thymol (10(-3) M), chlorpromazine (10(-3) M) and propranolol (10(-4) M), dissociated acinar cells were lysed as indicated by an increase in release of lactic dehydrogenase (LDH). 4. Ionophore A23187, CCK-PZ (maximal effective concentrations, 0.01 u. ml.-1), bethanechol (maximal effective concentrations, 10(-4) M) and glucagon increased amylase secretion in a dose-dependent fashion. Concentrations of CCK-PZ and bethanechol beyond optimal levels decreased amylase secretion. Concentrations of ionophore A23187 and glucagon when tested beyond 10(-6) M and 10(-4) M respectively increased the release of LDH. In concentrations that were non-toxic, membrane stabilizers blocked the stimulating effect of cholecystokinin-pancreozymin and bethanechol on amylase secretion but did not alter the response to A23187 and glucagon. 5. Unlike bethanechol, glucagon neither increased the uptake of 45Ca nor did it alter the release of 45Ca from cells previously loaded with 45CaCl2. 6. These data provide evidence that stimulus-secretion coupling in dissociated pancreatic acinar cells is basically similar to cells in situ. The effect of glucagon is consistent with the model in which hormone-dependent mobilization of Ca2+ from intra- or extracellular sources is bypassed leading to digestive enzyme secretion.

Stimulus secretion coupling: role of cyclic GMP and calcium in the regulation of secretion from rat exocrine pancreas

In rat pancreatic fragments, stimulation of amylase and labeled protein release by carbachol, caerulein, and ionophore A 23187 results within minutes in a short rise in cyclic GMP levels. Cyclic AMP levels do not change significantly. The secretory response elicited by each secretagogue is not modified when combined in pairs. Under intracellular calcium depleting conditions, both the cyclic GMP and the secretory responses to secretagogues are inhibited in parallel, suggesting a good correlation between both processes. Furthermore, 8-Bromocyclic GMP induces pancreatic secretion, but to a lesser extent, and fails to alter the increase in secretion caused by the various secretagogues. However, other agents such as imidazole, ascorbic acid, phenylhydrazine, and sodium azide also increase cyclic GMP levels but fail to stimulate pancreatic secretion. On the other hand, dibutyryl cyclic AMP also stimulates amylase and labeled protein discharge and potentiates the increase caused by cabachol, caerulein, and ionophore A 23187. These results do not permit conclusions regarding a cause and effect relationship between cyclic GMP and secretion. A role for calcium seems to be the most likely.

Effect of glucagon on digestive enzyme synthesis, transport and secretion in mouse pancreatic acinar cells

1. Effect of glucagon on amylase secretion and lactic dehydrogenase (LDH) release from functionally intact dissociated pancreatic acinar cells and acini was studied. 2. In dissociated rat pancreatic acinar cells, the rate of amylase secretion was increased by 70% with bethanechol (maximally effective concentration, 10(-4) M) and 125% with A23187 (10(-5) M), but the response to cholecystokinin-pancreozymin (CCK-PZ) was inconsistent. In dissociated cells from mouse pancreas, the increases amounted to 78% with bethanechol (10(-4) M), 134% with A23187 (10(-5) M) and 82% with CCK-PZ (maximally effective concentration, 0 . 01 u. ml.-1). Glucagon in concentrations ranging from 10(-7) to 10(-4) M increased amylase secretion by 3, 26, 67 and 80%, whereas secretin (10(-8)--10(-5) M) increased amylase secretion by 8, 39, 88 and 138%. LDH release was increased with A23187 in concentrations greater than 10(-6) M. 3. CCK-PZ, bethanechol and A23187 used in maximal concentrations potentiated the effect of a submaximal dose of glucagon whereas secretin did not have an additive or a potentiating effect. 4. Pancreatic acini were approximately 3 times more responsive to secretagogues than cells. The dose--response curves to bethanechol, glucagon and CCK-PZ for increase in amylase secretion were similar. LDH release was not increased by these agents. Cytochalasin B (5 microgram ml.-1) which is known to disrupt the integrity of luminal membrane inhibited the amylase secretion stimulated by glucagon, bethanechol and CCK-PZ. 5. Glucagon inhibited incorporation of a mixture of fifteen 14C-labelled amino acids (algal profile, Schwarz Mann) into perchloric acid precipitable proteins in dissociated mouse pancreatic acini within 30 min. 6. In 'pulse-chase' experiments, glucagon decreased the specific activity of zymogen granules isolated by differential centrifugation, from pancreatic lobules (120 min) and increased the specific activity of radiolabelled proteins in the medium (60 and 120 min). 7. It is concluded that glucagon increased digestive enzyme secretion from pancreatic acinar cells by a direct action (in contrast to its reported indirect effect in vivo) and decreased digestive enzyme synthesis. The data on transport and secretion do not support the suggested role of glucagon as an inhibitor in the intact animal.

Parallel secretion of enzymes by the rabbit pancreas

1. The purpose of this study was to determine whether or not the secretion of pancreatic enzymes by the rabbit remained proportional (parallel) after acute stimulation. 2. Hourly samples of pancreatic juice were collected from anaesthetized rabbits, each sample being analysed for volume, protein, amylase, trypsinogen and chymotrypsinogen. 3. Four groups of animals were studied for 2 hr before and 2 hr after stimulation with either saline (controls), methacholine, sincalide (C-terminal active octa-peptide of CCK-PZ) or CCK-PZ. 4. Despite a rise in protein output of more than 100% in the hour after stimulation in all experimental groups, there was no change in the specific activity (u./mg protein) of the three enzymes monitored, and the ratios of these enzymes to each other remained constant. 5. These results in the in vivo rabbit confirm our previous observation of parallel secretion in the in vitro rabbit pancreas; they are at variance with other studies in the rabbit (predominantly in vitro but also in vivo) which showed non-parallel secretion after CCK-PZ stimulation. 6. Our results tend to support the theory of mass transport and parallel secretion of pancreatic enzymes though no firm deductions on intracellular events can be made from juice analysis alone.

Effect of carbachol on radiosodium uptake by dispersed pancreatic acinar cells

The effects of carbachol on uptake of 22Na by enzymatically dispersed rat pancreatic acinar cells were determined. Carbachol caused a slight but significant increase in uptake of 22Na by the cells in the presence of absence of ouabain (10(-3) M). A maximal response was obtained with 10(-6) M carbachol. The effects of carbachol were blocked by 10(-5) M atropine. Caerulein (10(-7) M) also stimulated 22Na uptake, while epinephrine (10(-4) M) and substance P (10(-7) M) did not. Carbachol did not stimulate 22Na uptake in the absence of extracellular Ca, although Ca omission significantly elevated basal 22Na uptake. The divalent cationophore A-23187 caused Ca-dependent 22Na uptake at 20 microM concentration but not at 0.3 microM. These results, when considered with earlier reports by others, suggest that muscarinic receptor activation leads to an increase in permeability of the acinar cell membrane to Na, and that Ca may be second messenger for this effect.

Evidence against cyclic GMP as a mediator of the actions of secretagogues on amylase release from guinea-pig pancreas

In dispersed acini from guinea-pig pancrease several pancreatic secretagogues increased calcium outflux, cyclic GMP and amylase secretion, whereas nitroprusside and hydroxylamide increased cyclic GMP but did not increase calcium outflux or amylase secretion and did not alter the action of secretagogues on calcium outflux or amylase secretion. Secretin and vasoactive intestinal peptide increased cyclic AMP and increased secretion but did not alter cyclic GMP. Nitroprusside and hydroxylamine did not alter cyclic AMP or the action of secretin or vasoactive intestinal peptide on cyclic AMP and enzyme secretion. Agents that increased cyclic GMP also caused release of the nucleotide into the extracellular medium; however, this release did not correlate with secretion of amylase into the extracellular medium. 8-Bromo cyclic AMP as well as 8-bromo cyclic GMP increased enzyme secretion and potentiated the increase in enzyme secretion caused by cholecystokinin or carbachol. The increase in amylase secretion caused by vasoactive intestinal peptide or secretin plus either of the cyclic nucleotide derivatives was the same as that caused by the peptide alone. These results indicate that cyclic GMP does not mediate the action of secretagogues on pancreatic enzyme secretion, that the release of cyclic GMP into the extracellular medium does not occur by exocytosis and that the increase in enzyme secretion caused by 8-bromo cyclic GMP results from its ability to mimic the action of endogenous cyclic AMP.

Direct visualization of cell to cell coupling: transfer of fluorescent probes in living mammalian pancreatic acini

A technique whereby it is possible directly to observe the movement of organic molecules from cell to cell in living mammalian exocrine glands is described. Thin translucent segments of mouse pancreas are mounted in a superfusion bath. Fluorescent probes are injected intracellularly via fine micropipettes and fluorescence observed. Both fluorescein (mol. wt. 332) and procion yellow (mol. wt. 697) are shown to be transferred from the injection cell to neighbouring acinar cells. This shows directly the existence of intercellular communicating pathways.

Rat pancreas adenylate cyclase. VI. Role of the enzyme in secretin stimulated enzyme secretion

1. The responsiveness of adenylate cyclase and enzyme secretin for secretin and the C-terminal octapeptide of pancreozymin has been investigated in particulate fractions of the pancreas of five different species. 2. The adenylate cyclase is sensitive to the C-terminal octapeptide of pancreozymin in all species investigated. 3. The enzyme is much more sensitive to secretin in rat and cat than in mouse and rabbit, whereas with guinea pig intermediate values are obtained. 4. The enzyme secretion is stimulated by secretin in pancreatic fragments of rat and cat, but not in those of mouse and rabbit. 5. These results suggest that in species where secretin stimulated enzyme secretion, it does so by stimulating the adenylate cyclase system.