Quantitative energy dispersive X-ray microanalysis of eight elements in pancreatic endocrine and exocrine cells after cryo-fixation

SIDT2 is involved in the NAADP-mediated release of calcium from insulin secretory granules

The Sidt2 global knockout mouse (Sidt2(-/-)) has impaired insulin secretion. The aim of this study was to assess the role of SIDT2 protein in glucose-induced insulin secretion in primary cultured mouse β-cells. The major metabolic and electrophysiological steps of glucose-induced insulin secretion of primary cultured β-cells from Sidt2(-/-) mice were investigated. The β-cells from Sidt2(-/-) mice had normal NAD(P)H responses and KATP and KV currents. However, they exhibited a lower [Ca(2+)]i peak height when stimulated with 20mM glucose compared with those from WT mice. Furthermore, it took a longer time for the [Ca(2+)]i of β-cell from Sidt2(-/-) mice to reach the peak. Pretreatment with ryanodine or 2-aminoethoxydiphenyl borate (2-APB) did not change [Ca(2+)]i the response pattern to glucose in Sidt2(-/-) cells. Extraordinarily, pretreatment with bafilomycin A1(Baf-A1) led to a comparable [Ca(2+)]i increase pattern between these two groups, suggesting that calcium traffic from the intracellular acidic compartment is defective in Sidt2(-/-) β-cells. Bath-mediated application of 50nM nicotinic acid adenine dinucleotide phosphate (NAADP) normalized the [Ca(2+)]i response of Sidt2(-/-) β-cells. Finally, glucose-induced CD38 expression increased to a comparable level between Sidt2(-/-) and WT islets, suggesting that Sidt2(-/-) islets generated NAADP normally. We conclude that Sidt2 is involved in NAADP-mediated release of calcium from insulin secretory granules and thus regulates insulin secretion.

ELEMENTAL IMAGING IN PANCREAS OF IMMATURE RATS BY MICRO PIXE ANALYSIS

The pancreas is a large gland capable of both exocrine and endocrine functions; it releases digestive enzymes into the duodenum and hormones into the bloodstream. It is known that Zn plays a key role in the synthesis and action of insulin, one of the pancreatic hormones. However, elemental profiles of the pancreas are not well understood. Here, we examined precise distributions of elements in the pancreas of newborn and young rats by scanning microbeam particle induced X-ray emission (micro PIXE) analysis and compared the results to those of adult animals.

Micro PIXE analysis revealed a site-specific distribution of elements in the two major compartments of the pancreas, the exocrine (acinar tissue) and the endocrine portions (islets of Langerhans). The Zn concentrations in the pancreas of the newborn (six days), young (three weeks), and adult rats (ten weeks) were 11.3 ± 2.5 μ g / g wet weight, 7.26 ± 0.36 μ g / g wet weight, and 10.8 ± 1.1 μ g / g wet weight, respectively. In newborn and young rats, Zn was detected mainly in the islets of Langerhans, while K and P were distributed more to the acinar tissues than the islet cells. The site-specific distributions of K , P , and Zn were more obvious in the adult animals.

Analysis of zinc and other elements in rat pancreas, with studies in acute pancreatitis

Determination of the concentration of certain elements makes it possible to investigate the physiology of the pancreas. We used X-ray fluorescence to determine the concentrations of zinc and other elements in the pancreas of normal (control) rats and those with cerulein-induced pancreatitis. Ten elements (Zn, Ni, Fe, P, Ca, Cl, S, K, Ti, and Mn) were detected in controls. In the early stage of acute pancreatitis, the pancreatic concentrations of Zn, Ni, Fe, and P were significantly decreased (P < 0.05) and those of Ca and Cl were significantly increased (P < 0.05), compared with control levels. However, levels of S, K, and Ti did not differ significantly from the control values. Mn was detected in only some samples. The serum levels of Zn and Fe were significantly elevated (P < 0.05) in acute pancreatitis. These observations indicate that Zn and these other nine elements could play an important role in acute pancreatitis.

Regulation of the glutamate dehydrogenase activity in rat islets of Langerhans and its consequence on insulin release

Kinetic properties of glutamate dehydrogenase (GDH) and the effects on its activity of several putative modulators were examined in mitochondrial extracts of rat pancreatic islets. In the presence of 40 mmol/L NH4Cl and 0.1 mmol/L NADH, stepwise elevation of the 2-oxoglutarate concentration from 0.005 to 0.05 mmol/L increased glutamate formation, whereas further increases led to a progressive decrease of the reaction velocity. Adenosine diphosphate (ADP) at 0.1 mmol/L partially and at 1 mmol/L completely reversed the inhibitory effect of 2-oxoglutarate. The sensitivity to activation by either ADP or leucine was dependent on 2-oxoglutarate concentrations. At higher concentrations of the latter, greater amounts of the activators were needed to attain maximal effect. In the absence of allosteric activators, sulfate or phosphate at 20 mmol/L partially released the inhibitory effect of 2-oxoglutarate levels and increased the maximal velocity (Vmax) for the reaction. In the presence of 0.1 mmol/L ADP, both anions prevented the inhibition by higher concentrations of 2-oxoglutarate, whereas with 1 mmol/L ADP their only effect was a slight increase in the Vmax. Mg2+ and naturally occurring polyamines decreased glutamate formation in a dose-dependent manner; with 0.1 mmol/L ADP, inhibition was seen at all 2-oxoglutarate concentrations studied, whereas with 1 mmol/L ADP, it was noticeable at substrate concentrations higher than 0.5 mmol/L. This inhibitory effect on GDH activity was partially attenuated by sulfate. Addition of either 2 mmol/L spermidine or extra magnesium (final 2.5 or 5 mmol/L) to the perifusion buffer markedly attenuated the insulin release elicited by alpha-ketoisocaproate. It is suggested that naturally occurring polyamines, magnesium, and phosphate act as physiological modulators of GDH activity in pancreatic beta cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative X-ray microanalysis of P, Ca, and S in the mucus secretory granules of the cryofixed frog palate epithelium

In respiratory epithelium, the mucus is densely packed inside the secretory granules (SG) of secretory cells (SC) before being released by exocytosis in the airway lumen. We have previously shown that the frog palate is a representative model of respiratory epithelium and that rapid cryofixation is a very effective technique in preserving the integrity of the mucus SG. The concentration of phosphorus (P), sulphur (S), and calcium (Ca) were analysed inside the SG of the SC of frog palate after quick freezing, cryosubstitution, and embedding in Lowicryl resin at low temperature. The experiments were carried out using X-ray microanalysis conducted with energy dispersive spectrometry (EDS) at 100 kV. The quantitation was carried out using the continuum method with reference to Agar standards. The cryofixation permitted us to distinguish two types of SG depending on whether they were electron dense (serous cells) or electron-lucent (mucous cells). A significant (P < 0.001) difference in the S concentration was observed between the individual serous (239 +/- 79 mmol.kg-1) and the mucous SG (161 +/- 48 mmol.kg-1). No significant difference could be identified in the Ca concentration between the two SG phenotypes. In the serous SG, the P content was high (41 +/- 17 mmol.kg-1) compared with the mucous SG where it was not measurable. The comparison of the three element concentrations in each type of secretory cells showed that significant differences in concentration of S and Ca concentration could be observed from one SC cell to another.(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.