The role of magnesium in regulating CCK-8-evoked secretory responses in the exocrine rat pancreas

Fibroblast growth factor-23 and parathyroid hormone suppress small intestinal magnesium absorption

In the present study, we examined the systemic and direct effects of parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF-23) on duodenal, jejunal, and ileal Mg²⁺ absorption. The rats were injected with FGF-23 or PTH for 5 h before collecting the duodenum, jejunum, and ileum for Mg²⁺ transport analysis in Ussing chambers. The duodenum, jejunum, and ileum were directly exposed to FGF-23, PTH, or FGF-23 plus PTH with or without cell signaling inhibitors for 150 min in Ussing chambers prior to performing the Mg²⁺ transport study. The small intestinal tissues were also subjected to western blot analyses for FGF receptor (FGFR), PTH receptor (PTHR), Klotho, transient receptor potential melastatin 6 (TRPM6), and cyclin as well as the cystathionine β-synthase domain divalent metal cation transport mediator 4 (CNNM4) expression. The small intestine abundantly expressed FGFR and PTHR proteins, whereas, Klotho was not expressed in rat small intestine. Systemic PTH or FGF-23 injection significantly suppressed transcellular Mg²⁺ transport in the duodenum and jejunum. Direct FGF-23-, PTH-, or FGF-23 plus PTH exposure also suppressed transcellular Mg²⁺ absorption in the duodenum and jejunum. There was no additional inhibitory effect of PTH and FGF-23 on intestinal Mg²⁺ absorption. The inhibitory effect of PTH, FGF-23, or FGF-23 plus PTH was abolished by Gö 6850. Systemic PTH- or FGF-23-injection significantly decreased membranous TRPM6 expression, but increased cytosolic CNNM4 expression in the duodenum, jejunum, and ileum. In the present study, we propose a novel magnesiotropic action of PTH and FGF-23 by modulating small intestinal Mg²⁺ absorption.

Serum magnesium level as a predictor of acute kidney injury in patients with acute pancreatitis

BACKGROUND

Decreased serum magnesium (Mg²⁺) is commonly seen in critically ill patients. Hypomagnesemia is significantly more frequent in patients with severe acute pancreatitis. Acute kidney injury (AKI) in patients with acute pancreatitis (AP) is associated with an extremely high mortality. The association underlying serum Mg²⁺ and AKI in AP has not been elucidated.

AIM

To explore the association between serum Mg²⁺ on admission and AKI in patients with AP.

METHODS

A retrospective observational study was conducted in a cohort of patients (n = 233) with AP without any renal injury before admission to our center from August 2015 to February 2019. Demographic characteristics on admission, severity score, laboratory values and in-hospital mortality were compared between patients with and without AKI.

RESULTS

A total of 233 patients were included for analysis, including 85 with AKI. Compared to patients without AKI, serum Mg²⁺ level was significantly lower in patients with AKI at admission [OR = 6.070, 95%CI: 3.374-10.921, P < 0.001]. Multivariate logistic analysis showed that lower serum Mg²⁺ was an independent risk factor for AKI [OR = 8.47, 95%CI: 3.02-23.72, P < 0.001].

CONCLUSION

Our analysis indicates that serum Mg²⁺ level at admission is independently associated with the development of AKI in patients with AP and may be a potential prognostic factor.

Magnesium in man: implications for health and disease

Magnesium (Mg(2+)) is an essential ion to the human body, playing an instrumental role in supporting and sustaining health and life. As the second most abundant intracellular cation after potassium, it is involved in over 600 enzymatic reactions including energy metabolism and protein synthesis. Although Mg(2+) availability has been proven to be disturbed during several clinical situations, serum Mg(2+) values are not generally determined in patients. This review aims to provide an overview of the function of Mg(2+) in human health and disease. In short, Mg(2+) plays an important physiological role particularly in the brain, heart, and skeletal muscles. Moreover, Mg(2+) supplementation has been shown to be beneficial in treatment of, among others, preeclampsia, migraine, depression, coronary artery disease, and asthma. Over the last decade, several hereditary forms of hypomagnesemia have been deciphered, including mutations in transient receptor potential melastatin type 6 (TRPM6), claudin 16, and cyclin M2 (CNNM2). Recently, mutations in Mg(2+) transporter 1 (MagT1) were linked to T-cell deficiency underlining the important role of Mg(2+) in cell viability. Moreover, hypomagnesemia can be the consequence of the use of certain types of drugs, such as diuretics, epidermal growth factor receptor inhibitors, calcineurin inhibitors, and proton pump inhibitors. This review provides an extensive and comprehensive overview of Mg(2+) research over the last few decades, focusing on the regulation of Mg(2+) homeostasis in the intestine, kidney, and bone and disturbances which may result in hypomagnesemia.

Effect of magnesium supplementation and depletion on the onset and course of acute experimental pancreatitis

BACKGROUND AND OBJECTIVE

High calcium concentrations are an established risk factor for pancreatitis. We have investigated whether increasing magnesium concentrations affect pathological calcium signals and premature protease activation in pancreatic acini, and whether dietary or intraperitoneal magnesium administration affects the onset and course of experimental pancreatitis.

METHODS

Pancreatic acini were incubated with up to 10 mM magnesium; [Ca(2+)](i) (fura-2AM) and intracellular protease activation (fluorogenic substrates) were determined over 60 min. Wistar rats received chow either supplemented or depleted for magnesium (<300 ppm to 30 000 ppm) over two weeks before pancreatitis induction (intravenous caerulein 10 µg/kg/h/4 h); controls received 1 µg/kg/h caerulein or saline. C57BL6/J mice received four intraperitoneal doses of magnesium (NaCl, Mg(2+) 55 192 or 384 mg/kg bodyweight) over 72 h, then pancreatitis was induced by up to eight hourly supramaximal caerulein applications. Pancreatic enzyme activities, protease activation, morphological changes and the immune response were investigated.

RESULTS

Increasing extracellular Mg(2+) concentration significantly reduced [Ca(2+)](i) peaks and frequency of [Ca(2+)](i) oscillations as well as intracellular trypsin and elastase activity. Magnesium administration reduced pancreatic enzyme activities, oedema, tissue necrosis and inflammation and somewhat increased Foxp3-positiv T-cells during experimental pancreatitis. Protease activation was found in animals fed magnesium-deficient chow-even with low caerulein concentrations that normally cause no damage.

CONCLUSIONS

Magnesium supplementation significantly reduces premature protease activation and the severity of pancreatitis, and antagonises pathological [Ca(2+)](i) signals. Nutritional magnesium deficiency increases the susceptibility of the pancreas towards pathological stimuli. These data have prompted two clinical trials on the use of magnesium in patients at risk for pancreatitis.

Magnesium–calcium signalling in rat parotid acinar cells: effects of acetylcholine

This study investigated the effects of extracellular Mg(2+) ([Mg(2+)](o)) on basal and acetylcholine (ACh)-evoked amylase secretion and intracellular free Ca(2+) ([Ca(2+)](i)) in rat parotid acinar cells. In a medium containing 1.1 mM [Mg(2+)](o), ACh evoked significant increases in amylase secretion and [Ca(2+)](i). Either low (0 mM) or elevated (5 and 10 mM) [Mg(2+)](o) attenuated ACh-evoked responses. In a nominally Ca(2+) free medium, elevated [Mg(2+)](o) attenuated basal and ACh-evoked amylase secretion and [Ca(2+)](i). In parotid acinar cells incubated with either 0, 1.1, 5 or 10 mM [Mg(2+)](o), ACh evoked a gradual decrease in [Mg(2+)](i). These results indicate that the ACh-evoked Mg(2+) efflux is an active process since Mg(2+) has to move against its gradient. Either lidocaine, amiloride, N-methyl-D: -glucamine, quinidine, dinitrophenol or bumetanide can elevate [Mg(2+)](i) above basal level. In the presence of these membrane transport inhibitors, ACh still evoked a decrease in [Mg(2+)](i) but the response was less pronounced with either [Na(+)](o) removal or in the presence of either amiloride or quinidine. These results indicate marked interactions between Ca(2+) and Mg(2+) signalling in parotid acinar cells and that ACh-evoked Mg(2+) transport was not dependent upon [Na(+)](o).

Effects of Streptozotocin-Induced Type 1 Diabetes Mellitus on Total Protein Concentrations and Cation Contents in the Isolated Pancreas, Parotid, Submandibular, and Lacrimal Glands of Rats

This study investigated the effect of streptozotocin (STZ)-induced type 1 diabetes mellitus (DM) on total protein concentration and levels of sodium (Na+), potassium (K+), magnesium (Mg2+), zinc (Zn2+), copper (Cu2+), calcium (Ca2+), and iron (Fe2+) in the pancreas, parotid, submandibular, and lacrimal glands of the rat, compared to age-matched control animals. Protein concentrations were measured by the Bradford Assay, whereas levels of Na+, K+, Mg2+, Zn2+, Cu2+, Ca2+, and Fe2+ were measured by flame photometry and atomic absorbance spectrophotometry. The results show marked changes in the characteristics of diabetic and control animals. Diabetic rats and their different glands weighed significantly (P < 0.05) less compared to age-matched controls. Diabetic rats also have significantly elevated blood glucose and significantly reduced plasma insulin, compared to controls. The results also show that the concentrations of proteins and levels of cations were significantly (P < 0.05) reduced in the pancreas, parotid, submandibular and lacrimal glands of diabetic rats, compared to glands from age-matched animals. These differences in the cation contents and protein levels in STZ-induced DM in this study, along with supporting evidences from previous studies, may provide evidence for the development of long-term complications of DM including exocrine gland deficiencies.

Dietary-induced changes in the fatty acid profile of rat pancreatic membranes are associated with modifications in acinar cell function and signalling

The effects of dietary lipids on the fatty acid composition of rat pancreatic membranes and acinar cell function were investigated. Weaning rats were fed for 8 weeks on one of two diets which contained 100 g virgin olive oil (OO) or sunflower-seed oil (SO)/kg. Pancreatic plasma membranes were isolated and fatty acids determined. Amylase secretion and cytosolic concentrations of Ca(2+) and Mg(2+) were measured in pancreatic acini. Membrane fatty acids were profoundly affected by the diets; the rats fed OO had higher levels of 18 : 1n-9 (42.86 (sem 1.99) %) and total MUFA compared with the animals fed SO (25.37 (sem 1.11) %). Reciprocally, the SO diet resulted in greater levels of total and n-6 PUFA than the OO diet. The most striking effect was observed for 18 : 2n-6 (SO 17.88 (sem 1.32) %; OO 4.45 (sem 0.60) %), although the levels of 20 : 4n-6 were also different. The proportion of total saturated fatty acids was similar in both groups, and there was only a slight, not significant (P=0.098), effect on the unsaturation index. Compared with the OO group, acinar cells from the rats fed SO secreted more amylase at rest but less in response to cholecystokinin octapeptide, and this was paralleled by reduced Ca(2+) responses to the secretagogue. The results confirm that rat pancreatic cell membranes are strongly influenced by the type of dietary fat consumed and this is accompanied by a modulation of the secretory activity of pancreatic acinar cells that involves, at least in part, Ca(2+) signalling.

Calcium-magnesium interactions in pancreatic acinar cells

Although the role of calcium (Ca2+) in the signal transduction and pathobiology of the exocrine pancreas is firmly established, the role of magnesium (Mg2+) remains unclear. We have characterized the intracellular distribution of Mg2+ in response to hormone stimulation in isolated mouse pancreatic acinar cells and studied the role of Mg2+ in modulating Ca2+ signaling using microspectrofluorometry and digital imaging of Ca2+- or Mg2+-sensitive fluorescent dyes as well as Mg2+-sensitive intracellular microelectrodes. Our results indicate that an increase in intracellular Mg2+ concentrations reduced the cholecystokinin (CCK) -induced Ca2+ oscillations by inhibiting the capacitive Ca2+ influx. An intracellular Ca2+ mobilization, on the other hand, was paralleled by a decrease in [Mg2+]i, which was reversible upon hormone withdrawal independent of the electrochemical gradients for Mg2+, Ca2+, Na+, and K+, and not caused by Mg2+ efflux from acinar cells. In an attempt to characterize possible Mg2+ stores that would explain the reversible, hormone-induced intracellular Mg2+ movements, we ruled out mitochondria or ATP as potential Mg2+ buffers and found that the CCK-induced [Mg2+]i decrease was initiated at the basolateral part of the acinar cells, where most of the endoplasmic reticulum (ER) is located, and progressed from there toward the apical pole of the acinar cells in an antiparallel fashion to Ca2+ waves. These experiments represent the first characterization of intracellular Mg2+ movements in the exocrine pancreas, provide evidence for possible Mg2+ stores in the ER, and indicate that the spatial and temporal distribution of intracellular Mg concentrations profoundly affects acinar cell Ca2+ signaling.