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S S Rothman

Publications and source records attributed to S S Rothman.

At least 37 records · Page 2Linked to original sources
PubMed1983

Distribution of three hexose derivatives across the pancreatic epithelium: paracellular shunts or cellular passage?

It has been proposed that the pancreatic epithelium is permeable to three presumably passively distributed non-electrolytes, namely sucrose, inulin and mannitol, via paracellular shunts, and that the increased flux of sucrose and inulin seen during augmented digestive enzyme secretion is due to an increase in the permeability of these shunts. The present study considers this hypothesis by comparing the permeability of the epithelium to three different hexose derivatives, mannitol, inositol and 3-O-methyl-glucose, in both the unstimulated state and after the augmentation of protein secretion with a cholinergic drug. The epithelium was found to be more permeable to mannitol than to either inositol or 3-O-methyl-glucose. In the unstimulated state, the concentration of mannitol in ductal fluid at the steady state was approx. 54% of its concentration in the interstitium, as compared to 12% for inositol and 8% for 3-O-methyl-glucose. Cholinergic stimulation substantially increased the concentration of inositol and 3-O-methyl-glucose in secretion, but did not increase that of mannitol. The increase in the concentration of inositol occurred in the absence of an increase in its rate of transepithelial movement. Taken together, the results suggest that: (1) there is a substantial passage of mannitol through the cells of the epithelial layer, and (2) the increased concentration of inositol and 3-O-methyl-glucose in ductal fluid that occurs with stimulation is due to an increase in their efflux from secretory cells.

3-O-Methylglucose↗
PubMed1983

Protein concentration in the pancreatic zymogen granule.

We have estimated the concentration of protein in the zymogen granule, a major storage depot for secretory protein in the pancreatic acinar cell, in four different ways. Each of these approaches yielded roughly similar values. The protein concentration in the granule is approx. 135-270 mg protein/ml granule volume in rat and rabbit, as compared to an average value for the protein concentration of tissue of 135 mg/g tissue for rabbits and 183 mg/g tissue for rats. This is equivalent to an average molarity for the contained proteins of between 4-9 mM based on an estimated average molecular weight for the mixture of 30 000-40 000. An upper limit for the concentration of protein in these granules can reasonably be set at about double the overall concentration of protein in the non-granule portion of the cell.

Amylases↗
PubMed1983

Increase in zymogen granule volume accounts for increase in volume density during prenatal development of pancreas.

The sudden increase in volume density of zymogen granules in acinar cells of the fetal rat pancreas was examined with particular attention to the respective roles of granule size and number in this event. Volume density increased some twelvefold, from about 3% of cytoplasmic volume at 17 days to about 45% at 20 days, following a sigmoidal pattern in which the greatest rate of increase occurred during day 18. This increase in volume density was primarily the result of an increase in granule volume. Zymogen granule diameter increased from 0.55 micron at 17 days to 1.20 micron at 20 days, an order of magnitude increase in average granule volume. The total number of granules in the tissue increased in proportion to the increase in organ weight (cell number and size), but changes in the number of granules per unit cytoplasmic volume were minor (+ 40%) in comparison to the increase in volume density. The distribution of granule diameter was roughly normal and unimodal at each time interval, and the increase in average diameter over time was marked by an increase in the upper limit of the size distribution and an increased percentage of large granules. The size of condensing vacuoles also increased during this period, and their distributions were roughly coextensive with those seen for zymogen granules at the same time. The potential origins of changes in granule size are discussed, as well as the important effect that size has on the number of granules observed in "two-dimensional" tissue sections viewed in the electron microscope. If size is not considered in our estimates, then we underestimate the numerical density in cells with small granules compared to those with large granules. The results indicate the central role of granule size, as opposed to number, in determining granule volume density in the embryonic pancreas.

Animals↗
PubMed1983

Pancreatic epithelium is permeable to sucrose and inulin across secretory cells.

The pancreatic epithelium is permeable to both sucrose and inulin and becomes more permeable when protein secretion by the gland is stimulated. Because these molecules are not thought to enter cells, it has been assumed that their movement across the epithelium from interstitial to ductal fluid, as well as the increase in that flux that is observed during augmented protein secretion, is due to their passage through paracellular shunts. In the present experiments we have considered the alternative possibility that sucrose and inulin travel through the cells of the secretory epithelium instead of, or in addition to, their passage through paracellular shunts. The data support this view and suggest that the pancreas is unusually permeable to water soluble molecules of substantial size by means of a transcellular pathway.

Animals↗
PubMed1983

Increased phosphate efflux from acinar cell during protein secretion.

The permeability of the pancreatic epithelium to two water soluble molecules, sucrose and inulin, increases when protein secretion is augmented by a cholinergic agonist. An increase in the permeability of passive paracellular shunts (3) has been proposed to account for these observations. In the present experiments we have measured the distribution of another molecule, phosphate ion, across the epithelium by following its secretion from the cannulated duct of whole-rabbit pancreas in short-term organ culture. A cholinergic stimulant increases phosphate ion concentration in secretion in a similar fashion to that seen for the watersoluble nonelectrolytes. However, both the unstimulated rate of phosphate secretion and the increase observed with cholinergic stimulation were not dependent on the presence of the ion in the medium, and therefore its secretion in both cases reflects phosphate efflux from the cell and not its paracellular transport. The results indicate that either the phosphate ion is excluded from paracellular shunts or that such shunts do not contribute substantially to the transpancreatic passage of molecules of this size.

Animals↗
PubMed1983

Origin of the decline in pancreatic amylase secretion with time in vitro.

The release of alpha-amylase (EC 3.2.1.1) into the medium bathing strips of rabbit pancreas decreased gradually with time in vitro so that after 3 h of incubation the secretory rate was only 20% of that seen initially. This decrease was not the result of an intrinsic loss of cellular responsiveness or viability, because a cholinergic agonist was still able to augment amylase secretion from the tissue after this incubation period to the same, or greater, degree than from "fresh" tissue. Rather, the inhibition of secretion was apparently due to the release of a nondialyzable substance from the tissue, which appears to be amylase itself. The observations that led to this conclusion are 1) replacing the bathing medium every 30 min eliminated the time-dependent decrease in enzyme secretion, 2) this replacement was ineffective if the tissue was separated from the medium by a dialysis membrane, and 3) adding an excess of the amylase substrate glycogen to the medium also prevented the falloff in amylase secretion, the effect of glycogen presumably being due to the formation of an enzyme-substrate complex in the medium. These observations are consistent with other observations that demonstrate that the rate of enzyme secretion by the pancreas depends on the rate of removal of product from the site of its secretion [Isenman and Rothman, Proc. Natl. Acad. Sci. USA 74: 4068-4072, 1977; Isenman and Rothman, Science 204: 1212-1215, 1979; Ho and Rothman, Am. J. Physiol. 242 (Gastrointest. Liver Physiol. 5): G32-G39, 1982].

Amylases↗
PubMed1982

Redistribution of amylase activity accompanying its secretion by the pancreas.

Amylase activity in several tissue and body fluid compartments in the rat changed markedly when the secretion of digestive enzyme was augmented over a 3-hr period with a cholinergic agonist. As a result of stimulation, the pancreas was depleted of about one-third of its amylase activity and accounted for only 75% of the amount recovered from the animal, compared to 92% in the fasted state. Despite the continuous augmented secretion of the enzyme into the small intestine, no increase in amylase activity was detected there at the end of 3 hr. On the other hand, amylase activity in plasma and extracellular fluid increased by about an order of magnitude and accounted for 13% of the total pool, compared to approximately 1% in the fasted state. Amylase activity in several solid tissues also increased, including a 50- to 100-fold increase in parotid gland and an almost 10-fold increase in submandibular gland and kidney. The potential sources of the increased amylase activity in blood, the endocrine secretion of the enzyme by the pancreas, and its absorption from the intestine are considered. Changes in the amylase content of various tissues appear to reflect increased uptake due to increased plasma levels.

Amylases↗
PubMed1982

Nature of flow dependence of protein secretion by the exocrine pancreas.

It has been proposed that bidirectional and concentration-dependent fluxes of digestive enzymes across pancreatic acinar cell membranes account for secretion. One implication of such a model is that protein secretion should be a function of fluid outflow, inasmuch as flow would be required to generate the necessary concentration gradient by carrying away secreted material. In an earlier study (Science 204: 1212, 1979) when fluid flow was decreased by a backpressure applied to fluid in the pancreatic duct, proportional reductions in protein secretion occurred. The present study uses metabolic rather than mechanophysical methods to decrease flow, reduction of the sodium concentration of the medium bathing the pancreas, or addition of the Na+-K+-ATPase inhibitor ouabain. Both treatments produced similar results: decreases in protein output synchronous with and proportional to the observed decreases in flow. Essentially the same relationship was seen when flow was reduced during protein secretion augmented by the secretagogue cholecystokinin-pancreozymin. These results suggest that the reduction in flow rate (whether produced mechanically or chemically) was the variable directly responsible for the decrease in protein secretion by the acinar cell.

Animals↗
PubMed1982

Effect of changes in circulating amylase levels on amylase output in bile.

The relation between plasma and biliary amylase activity and their relationship to the functional state of the pancreas were studied in anesthetized rabbits. Repetitive intravenous injections of cholecystokinin resulted in a 25-fold rise in the secretion of amylase via the pancreatic duct, followed at first by a 50% increase in plasma amylase concentration and later by a 270% increase in biliary amylase concentration. There was then a gradual, roughly synchronous decline in both plasma and biliary values toward basal level despite a continued highly augmented rate of pancreatic ductal secretion. "Near-total" pancreatectomy completely abolished the effect. These observations are consistent with a cholecystokinin-induced basolateral secretion of amylase from pancreas into blood and its subsequent movement from blood into bile down a concentration gradient. The output of amylase in bile, however, was quite small and does not suggest that biliary transport of amylase has an important function either as a means of secreting and recycling digestive enzyme into the gut or as a major excretory pathway for circulating amylase in the rabbit.

Amylases↗
PubMed1982

Food, duodenal extracts, and enzyme secretion by the pancreas.

Previous studies have reported that injection of duodenal extracts from rats fed different meals into the celiac artery of recipient rats elicited the secretion of related pancreatic enzymes. We have been unable to reproduce the enzyme-specific increases in the average output of particular enzymes that were observed but did find changes similar in direction, although not magnitude, to those reported previously. The outputs of amylase and trypsinogen were compared by plotting individual data points and performing a regression analysis on them. The injection of duodenal extracts from lactalbumin hydrolysate-fed rats led to trypsinogen secretion being favored over that of amylase and vice versa for extracts from rats fed a glucose meal. In addition, it was found that cholecystokinin-pancreozymin produced a dramatic nonparallel transport of these two enzymes with amylase secretion being augmented to a greater degree than trypsinogen secretion. The relation between their outputs was curvilinear, i.e., the amylase dominance of secretion became more pronounced as overall enzyme output (not dose of hormone) increased. Thus, this nonparallel secretion does not seem to be the results of a discontinuous switch in the character of enzyme secretion produced by the hormone but a graded effect reflecting the magnitude of the response.

Amylases↗
PubMed1981

Zymogen granules of pancreas decrease in size in response to feeding.

In the first descriptions of pancreatic enzyme secretion about 100 years ago, it was noticed that zymogen granules became smaller and disappeared from the apical region of acinar cells after feeding. We have repeated these experiments and characterized changes in granule size by quantitative electron microscopy 90 min after feeding previously fasted rats. In fasted animals, granules occupied the apical portion of the cell, had an average number of 45 +/- 3 granules per cell section (+/- SE), and measured 0.85 +/- 0.15 micrometers in diameter (+/- SD). After feeding, the number and size of granules decreased. Individual samples showed either a decrease in size alone or a decrease in both size and number, but in no case did they show a reduction in granule number alone. The mean diameter of granules decreased to 0.65+/- 0.15 microns (+/- SD) or about a 55% reduction in average granules volume as compared to controls (0.32 vs. 0.14 microns 3). The size distributions were unimodal and normal in both fasted and fed rats; however, in fed animals, the distribution was shifted to lower values (diameter range 0.40-1.40 microns for fasted rats vs. 0.10-1.30 microns for fed rats). The number of granules decreased to an average of 29 +/- 2 granules per cell section (+/- SE) after feeding, and, on the average, samples with the most granules had larger ones than samples with the fewest granules. The present results support the original observations on live rabbit pancreas that individual granules decrease in size in response to feeding. We suggest that these size changes reflect the loss of proteins across the granule membrane as proposed by the equilibrium hypothesis for digestive enzyme secretion.

Animals↗
PubMed1981

Digestive end products mobilize secretory proteins from subcellular stores in the pancreas.

Two digestive end products, D-glucose and L-lysine, produced substantial concentration-dependent release of amylase and trypsinogen, respectively, from subcellular storage pools into a postmicrosomal supernatant fraction of rat pancreatic tissue homogenate. This process was selective in that D-glucose did not lead to trypsinogen release, while L-lysine did not effect amylase. An analogue of D-glucose, 2-deoxy-D-glucose, was much less potent than D-glucose on an equimolar basis. Half-maximal release for both end-product enzyme pairs occurred at concentrations within the range of normal plasma values for these end products in the rat. Although amylase release reached an apparent plateau when the concentration of glucose was increased beyond the maximally effective level, lysine concentrations higher than that maximally effective resulted in a fall in trypsinogen release that ultimately returned (at 3.0 mM L-lysine) to the level seen in its absence. When isolated zymogen granules were exposed to the same concentrations of D-glucose or L-lysine, a similar pattern of release was seen, indicating that the zymogen granules are a source of the enzymes released from the particulate phase of the homogenates. These findings can be explained most simply by the selective movement of digestive enzymes across zymogen granule membranes in response to the presence of appropriate end products. They are also consistent with the concept that digestive end products can act rapidly and directly on the pancreatic acinar cell to regulate the mixture of enzymes secreted in response to the specific hydrolytic needs of a meal.

Amylases↗
PubMed1981

Endocrine secretion of alpha-amylase by the pancreas.

The effect of the gastrointestinal hormone, cholecystokinin-pancreozymin (CCK-PZ), on the flux of alpha-amylase across the basolateral surface of the pancreas into interstitial fluid was measured by following its appearance in the medium bathing whole rabbit pancreas in organ culture. CCK-PZ increased the rate of amylase release by about an order of magnitude for the maximum applied dose. The response was only observed at concentrations of CCK-PZ that were supramaximal for ductal enzyme secretion (320 pmol/l to 10 nmol/l). Over this range, amylase secretion into the bath varied widely with dose, whereas that into the duct remained relatively unchanged. These observations, in conjunction with others, suggest that the acinar cell, and not the duct system, is the direct source of this amylase and that there is a natural secretion of digestive enzyme from the acinar cell in the endocrine direction that is augmented by CCK-PZ or a homologous peptide.

Animals↗