Effects of reserpine and isoproterenol on elemental distribution in submandibular gland of rat

Chloride secretion in the submandibular gland of adult and early postnatal rats studied by X-ray microanalysis

Submandibular acinar cells of 1-day-old, 7-day-old, and adult rats were analyzed with X-ray microanalysis after stimulation with carbachol for different time periods (2-7 min). In unstimulated animals, marked differences in elemental content between compartments could be observed: secretory granules had a higher Ca and lower P and K content than other cell compartments. Comparison between different age groups showed significant differences for Ca, which increased with age in all compartments; Mg increased with age in the secretory granules and the apical cytoplasm. Only the glands from adult animals showed a significant effect of cholinergic stimulation: a transient decrease in Cl and K. The Cl concentration in the secretory granules decreased to 60% of the control value, which suggests that the granules release Cl upon stimulation. In young animals, no or little change in elemental distribution was observed after stimulation. This may indicate that Cl- secretion mechanisms are much less prominent in young animals. The ultrastructure of submandibular secretory granules depends on the preparation method: condensed and electrondense in freeze-substituted unfixed tissue, decondensed and more translucent in aldehyde-fixed tissue. This may indicate that the granules can transport water, and swell during the process of aldehyde fixation.

A review of electron probe X-ray microanalysis studies of salivary gland cells

Electron probe X-ray microanalysis (EPXMA) has now been successfully applied to several salivary gland preparations. This paper briefly reviews the principles underlying this technique and the specific sample preparation procedures which permit accurate measurement of elemental concentrations in the various intracellular spaces. Findings from salivary gland studies indicate that cytoplasmic and nuclear spaces of nonstimulated acinar cells have high concentrations of K and P, and low concentrations of Mg, Ca, and S; and that mature secretory granules have high concentrations of Ca and S, and relatively low concentrations of K and P. No consistent differences have been found between the elemental concentrations of mucous and serous secretory granules. In vivo and in vitro EPXMA studies of the elemental changes associated with secretory granule maturation indicate there are at least two stages in this process: an early stage during which granule S concentration increases in parallel with mass density as condensing vacuoles mature into secretory granules, and a late stage during which granule mass density and protein content increase with no further elemental concentration changes. Findings from other in vivo and in vitro studies indicate that secretory granule membranes are permeable to Na, K, and Cl ions because the granular concentrations of these elements are altered by electrochemical gradients. Recent EPXMA results indicate that cells stimulated with parasympathomimetic agonists have decreased K and Cl concentrations, and increased Na concentrations. Furthermore, the magnitude of these changes are quantitatively consistent with changes measured using radio-isotope equilibration and other techniques. In contrast, cells stimulated with the beta-adrenergic agonist, isoproterenol, have increased concentrations of Na and Cl, but unchanged K concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Elemental composition of secretory granules in pancreatic islets of Langerhans

We have characterized, by electron probe microanalysis, rapidly frozen cultured rat islets at the level of individual secretory granules. Elemental analysis of thin, dried cryosections showed that beta granules could be distinguished by high Zn, Ca, and S, whereas non-beta (mainly alpha) granules contained elevated P and Mg. Although a single granule type predominated in a particular cell, some rebel granules were found in A cells that had the compositional fingerprint of B cell granules. Zn, which was found in millimolar concentrations in B cell granules, was considered a marker for the insulin storage complex. The data indicate that non-B islet cells in the adult pancreas may produce insulin-containing organelles and that, when glucagon and insulin are coexpressed, these hormones are packaged in separate granules.

Abnormal 45Ca fluxes in dispersed submandibular acini of rats treated with reserpine

The uptake and efflux of the isotopic tracer 45Ca were compared in dispersed submandibular acini of both control rats and rats treated with seven daily doses of reserpine (0.5 mg/kg, i.p.). Tracer uptake occurred in a time-dependent manner in both types of acini and reached 8.4 +/- 0.2 and 8.0 +/- 0.2 pmol/mg protein, respectively, in acini from control and treated animals after 60 min of incubation. Uptake of tracer was 2.35 nmol/mg DNA in control cells and 4 nmol/mg DNA in cells from treated rats at 60 min. 45Ca uptake (per mg protein) was enhanced in control acini 48% by 20 mumol/L epinephrine; 38% by 50 mumol/L carbachol; and 23% by 10 mumol/L isoproterenol. A similar order of potency was observed when uptake was expressed per mg DNA. In acini from reserpine-treated rats, 45Ca uptake (per mg protein) was increased 53% by epinephrine, 39% by isoproterenol, and only 8% by carbachol. The same enhanced effect of isoproterenol and lack of effect of carbachol were observed when uptake was calculated per mg DNA. In the absence of secretagogue, efflux of 45Ca from tracer-pre-loaded acini was larger in acini from reserpine-treated rats (53%) than in control acini (36%). Whether expressed in terms of mg protein or mg DNA, this efflux was increased in control acini 35% by epinephrine, from 25 to 28% by isoproterenol, and 17% by carbachol. In acini of reserpine-treated rats, epinephrine increased 45Ca efflux 20%, isoproterenol from 25 to 28%, and carbachol from 14 to 15%.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular elemental concentrations in resting and secreting rat parotid glands

Electron probe x-ray micro-analysis was used to study the elemental concentration changes that occur during pilocarpine-stimulated saliva secretion. Quantitative x-ray micro-analysis of elemental concentrations in intracellular compartments of rat parotid glands stimulated in vivo with pilocarpine showed that Na concentration was significantly increased, while K concentration was significantly reduced. The magnitude of these changes was consistent with values obtained in other tissues with the x-ray micro-analysis method, and in the same tissue with other experimental methods. Comparisons with results from studies utilizing dispersed acini suggest that acinar dispersion procedures may affect intracellular elemental concentrations. Total electrolyte concentrations in cytoplasm and secretory granules were estimated to increase on a dry-weight basis following pilocarpine stimulation. The former change is consistent with the notion of a transcellular route of salivary fluid flow, while the latter change may be important in the exocytosis of secretory granules.

Changes in elemental concentrations of rat parotid acinar cells following pilocarpine stimulation

1. Quantitative electron microprobe analysis was used to measure elemental dry weight concentrations in cytoplasm, secretory granules and nuclei of resting and pilocarpine-stimulated rat parotid gland acinar cells. 2. Secretory granules in resting cells had lower concentrations of Na, Mg, P, Cl and K, and higher concentrations of S and Ca than cytoplasm or nuclei. Nuclei in resting cells had lower S and higher K concentrations than cytoplasm. 3. Three major pilocarpine-related changes were found: (i) cytoplasmic dry weight concentrations of Na and Ca increased and the concentration of K decreased, (ii) the nuclear concentration of Na increased while that of K decreased and (iii) the concentrations of Na and Cl increased in secretory granules. 4. These results indicate that the nuclear, and cytoplasmic compartments have different mechanisms for regulating their elemental concentrations relative to the secretory granules. 5. The present results are largely consistent with X-ray microanalysis results from the pilocarpine-stimulated dog submandibular gland.

Effects of calcitonin on elemental distribution and ultrastructure of rat submandibular gland acinar cells

The effect of calcitonin on rat submandibular gland acinar cells was investigated by X-ray microanalysis and electron microscopy. Calcitonin caused a transient increase of the cellular calcium and magnesium concentration, but did not affect the intracellular concentration of other electrolytes. The relative volume of intracellular mucus increased from 45% in control glands to 72% at 6 h after administration of calcitonin. Calcitonin caused an inhibition of the cellular response of the acinar cells to beta-adrenergic and cholinergic agonists. The changes in elemental composition and ultrastructure of the gland cells are probably due to inhibition of mucus release from the cells.

Effect of chronic treatment with cystic fibrosis fibroblast medium on rat submandibular gland acinar cells

The effect of chronic treatment with cystic fibrosis (CF) fibroblast medium on rat submandibular gland and pancreas was investigated. Rats were injected for 8 days with conditioned medium from normal or CF fibroblasts. The elemental content of the acinar cells was measured by X-ray microanalysis of cryosections. A significant increase in cellular calcium, and a decrease in cellular sodium concentrations were found after treatment with CF medium. The ultrastructure of the submandibular acinar cells was not affected by the conditioned CF fibroblast culture medium. No effect of treatment with CF medium on ultrastructure and elemental content of pancreatic acinar cells could be demonstrated. The response to alpha-adrenergic, beta-adrenergic, cholinergic, and peptidergic stimulation in submandibular gland acinar cells of rats injected with normal or CF medium was investigated in vitro. With regard to changes in elemental composition after stimulation, no significant differences in response between the two groups could be found. Apparently, a factor in conditioned medium from cultured CF fibroblasts induces a net increase in calcium content of rat submandibular gland acinar cells. Possibly, this factor acts in a similar way in CF patients and may cause elevated calcium levels in CF cells.

The chronically pilocarpine-treated rat in the study of cystic fibrosis: investigations on submandibular gland and pancreas

The chronically pilocarpine-treated rat has been proposed as an animal model for the disease cystic fibrosis, a generalized exocrinopathy. The effect of chronic pilocarpine treatment on structure, composition, and function of the acinar cells of rat submandibular gland and pancreas was investigated by electron microscopy, X-ray microanalysis, and biochemical analysis. The morphological effects of chronic pilocarpine treatment were most pronounced in the pancreas. The number and size of the zymogen granules was increased, and the granules had a less electron-dense appearance. X-ray microanalysis at the cellular level showed in both the submandibular gland and the pancreas a significant increase in calcium and a decrease in sodium. The increase in cellular calcium concentrations can be explained by an increase in the relative volume of secretory material in the cell (assessed by morphometry) and an increase in the local calcium concentration in the secretory material (assessed by X-ray microanalysis at the subcellular level). Chronic pilocarpine treatment caused a disturbance of glycolysis and energy metabolism in the submandibular gland, but no significant effects in this respect were noted in the pancreas. On the other hand, a nearly twofold increase of the pancreatic amylase activity was noted. The pancreas appeared somewhat hyperreactive towards cholinergic stimulation.