Plasma Magnesium Concentrations Research Articles

Magnesium concentration in plasma, leukocytes and urine of children with intermittent asthma

Background: Magnesium (Mg) is involved in numerous physiological functions, including protein folding, intracellular signalling and enzyme catalysis. It acts as a smooth muscle relaxant. We decided to test changes of total Mg concentration in plasma, leukocytes and urine of 16 healthy children and 26 patients with intermittent asthma aged 3 to 14 years. Methods: Samples were taken on the first day of bronchoobstruction and five days after the acute attack. During this period, patients were under salbutamol therapy. Results: Plasma Mg concentration in patients increased by about 40% (first day 0.58±0.05 mmol Mg/l and five days later 0.64±0.04 mmol Mg/l) compared with healthy children (0.42±0.04 mmol Mg/l). Leukocyte Mg concentrations showed significant changes. On the first day of bronchoobstruction, Mg in leukocytes significantly decreased by about 60% (1.16±0.31 mmol Mg/g protein) compared to healthy children (3.04±0.68 mmol Mg/g protein). Five days later, Mg values significantly increased (3.28±1.09 mmol Mg/g protein) and almost reached the values of the healthy group. Mg concentration in urine statistically decreased by about 30% (0.55±0.06 mmol Mg/mmol creatinine) on the first day of bronchoobstruction compared to healthy children (0.75±0.05 mmol Mg/mmol creatinine). Five days after the acute attack, Mg concentration in patients' urine (0.73±0.07 mmol Mg/mmol creatinine) was close to values of healthy children. Conclusion: The results obtained indicate that the intracellular measurement of Mg concentration is relevant for estimation of magnesium concentration in the human organism. Hence, determination of Mg concentration in lekocytes may be used in evaluation of asthmatic pathology.

Iatrogenic hypocalcaemia during parenteral fluid therapy of diarrhoeic calves

Acid-base balance and electrolyte concentrations, including ionised calcium, were monitored during intravenous fluid therapy of 1 1 collapsed diarrhoeic suckler calves aged five to 10 days. Six healthy calves of...

Plasma ionized calcium and parathyroid hormone concentrations in horses after endurance rides

To evaluate changes in plasma ionized calcium (Ca2+) and parathyroid hormone (PTH) concentrations in horses competing in endurance rides. Longitudinal clinical study. 28 horses. Venous blood samples were obtained from horses before and after racing 80 km. Plasma pH and concentrations of Ca2+, PTH, inorganic phosphorus, albumin, lactate, and magnesium were measured. Overall, a significant decrease in mean (+/- SD) plasma Ca2+ concentration (from 6.44 +/- 0.42 to 5.64 +/- 0.42 mg/dl) and a significant increase in plasma PTH concentration (from 49.9 +/- 30.1 to 148.1 +/- 183.0 pg/ml) were found after exercise. Exercise also resulted in significant increases in plasma inorganic phosphorus, albumin, and lactate concentrations. No changes in plasma magnesium concentration or pH were detected after exercise. Plasma PTH concentration was not increased after exercise in 8 horses; in these horses, plasma PTH concentration decreased from 58.2 +/- 26.3 to 27.4 +/- 22.4 pg/ml, although plasma Ca2+ concentration was also decreased. Plasma Ca2+ concentration was decreased after racing for 80 km, compared with values obtained before racing. In most horses, an increase in plasma PTH concentration that was commensurate with the decrease in plasma Ca2+ was detected; however, some horses had decreased plasma PTH concentrations.

Magnesium, zinc and iron levels in pre-eclampsia.

To determine the change in erythrocyte and plasma magnesium, plasma zinc and serum iron concentrations in pre-eclampsia. Twenty women with pre-eclampsia and 20 control subjects matched for gestational age were examined. The levels of magnesium, zinc and iron in all subjects were measured by flame atomic absorption spectrometry. In the pre-eclamptic women, who were supplemented with magnesium salts, these measurements were repeated after delivery. The intraerythrocytic magnesium levels before supplementation were significantly lower in the pre-eclamptic patients than in the healthy pregnant women (0.98 +/- 0.15 vs. 1.35 +/- 0.30 mmol/l; p < 0.001) and increased (to 1.25 +/- 0.25 mmol/l) after treatment with magnesium. The plasma magnesium and zinc, and the serum iron concentrations were not significantly different between the pre-eclamptic and the healthy pregnant women. Our results suggest that low cellular magnesium levels in women with pre-eclampsia may contribute to the development of hypertension in these patients, and that the measurements of plasma zinc and serum iron concentrations are of doubtful clinical value in the management of pre-eclampsia.

Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in cattle

Severe hypomagnesaemia and tetany were induced in 10 lactating cows by feeding them semi-synthetic low magnesium diets and the animals were used to study the stability of postmortem markers of...

The impact of calcium, magnesium, zinc, and copper in blood and seminal plasma on semen parameters in men

To investigate the impact of calcium, magnesium, zinc, and copper in blood and seminal plasma on semen parameters, 107 fertile and 103 subfertile males provided a standardized blood and semen specimen. Total calcium and magnesium concentrations were determined with colorimetric end point assay procedures. Zinc and copper were determined by flame atomic absorption spectrophotometer (AAS). Semen analysis was performed according to World Health Organization guidelines (1992). The concentrations of calcium, magnesium, zinc, and copper in blood and seminal plasma were not different between the subfertile and fertile group. Weak correlations were demonstrated between blood plasma zinc concentrations and sperm count (r s = 0.18), sperm motility (r s = 0.15), and abnormal sperm morphology (r s = 0.13). Zinc and magnesium concentrations in seminal plasma correlated weakly with sperm count (r s = 0.17 and r s = 0.16, respectively), and copper concentrations in blood plasma with motility (r s = 0.25). Strong correlations were found between calcium, magnesium, and zinc in seminal plasma. Although calcium, magnesium, zinc, and copper play an essential role in spermatogenesis and fertility, the determination of these elements in blood and seminal plasma does not discriminate on the basis of fertility in this group of men.

Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in sheep

Hypomagnesaemic tetany was induced in non-lactating and lactating ewes by feeding them semi-synthetic low magnesium diets containing additional potassium chloride and citric acid. Aqueous and vitreous humour were sampled from...

Ranges of Regulation of Sodium, Potassium, Calcium, Magnesium Concentrations in Plasma, Erythrocytes, and Muscle Tissue of Rutilus rutilus under Natural Conditions

As a result of studies for 3 years on the roach Ratilus ratilus under natural conditions, it was shown that the Na, K, Ca, and Mg content in the blood plasma, erythrocytes, and muscle tissue as well as muscle water were maintained year after year within definite ranges characterizing normal values for these parameters. Comparison of variations in the Na, K, Ca, Mg blood plasma concentrations in different fish species revealed the presence of common limits for each of these elements. Throughout the year the most essential changes in the roach blood and tissue cation levels were found during reproduction period. During spawning the fish are characterized by the state of acute stress with parameters indicating a decrease in stability and exhaustion of adaptive possibilities in animals. Intensification of defense reactions, including those providing maintenance of the water–salt homeostasis occurs shortly before spawning for a preliminary preparation to the stress situation.

Cardiovascular Actions of Magnesium

Intracellular magnesium is an important modulator of calcium and potassium channels in cardiac myocytes. Hypomagnesemia is common in hospitalized patients and may contribute significantly to cardiac morbidity and mortality, particularly in states associated with myocardial ischemia. Therefore, it is important to maintain the plasma magnesium concentration within the normal range in asymptomatic patients and in patients with cardiac disease as prophylaxis against the occurrence of significant arrhythmias.

Evaluation of Serum Magnesium Concentration Changes in Orthotopic Liver Transplant Patients

Background: During orthotopic liver transplantation, magnesium monitoring has been done frequently because of its important role in the cardiovascular system. Generally hypomagnesemia may occur frequently during an operation, but some investigators reported serum magnesium levels returned to normal after reperfusion which is different from our result. Therefore, this study was done to confirm the changes of serum magnesium in the postanhepatic stage and also to confirm the need for prophylactic magnesium administration. Methods: Thirteen patients plasma magnesium concentrations were measured 8 times during the operation on each patient. We also checked the total transfusion amount and required CaCl2 amount in every patient. The significance of all data were evaluated with a paired t-test and correlation method. Results: Serum magnesium levels were significantly decreased after the beginning of the postanhepatic stage during an operation (P < 0.05). Correlation between transfused blood amounts and CaCl2 requirements showed significant correlation (r: 0.709), but no correlation between magnesium concentrations and transfused blood amounts was found. Conclusions: We concluded that serum magnesium concentrations were significantly decreased especially in the postanhepatic stage and an appropriate amount of a magnesium supply may be needed. (Korean J Anesthesiol 2001; 40: 733∼737) ꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏ

Intravenous amiodarone or magnesium sulphate is not cost-beneficial prophylaxis for atrial fibrillation after coronary artery bypass surgery

Our aims were to examine whether the administration of amiodarone or magnesium sulphate after coronary artery bypass graft surgery (CABG) could reduce the occurrence of atrial fibrillation, and to identify the risk factors associated with atrial fibrillation after CABG. Patients scheduled for elective CABG (n = 155) were allocated randomly, in a controlled double-blind study, to receive immediately after surgery a 72-h infusion of amiodarone (900 mg per 24 h), magnesium (4 g per 24 h) or placebo (0.9% NaCl; 50 ml per 24 h) intravenously. A 72-h Holter ECG was recorded concomitantly. The primary end-point was the prevention of atrial fibrillation; its onset was considered as prophylactic failure. An interim safety analysis was performed in 147 patients. The cumulative occurrence of atrial fibrillation was 27% in the placebo group, 14% in the amiodarone group (P = 0.14) and 23% in the magnesium group (P = 0.82). Although amiodarone delayed the onset of the first tachyarrhythmic episode (P = 0.02), it was associated with the need for longer periods of vasoactive drug infusion and invasive monitoring and a longer stay in the intensive care unit. Variables associated with the onset of atrial fibrillation were older age (odds ratio 1.9) and a plasma magnesium concentration at 24 h of less than 0.95 mmol litre-1 (odds ratio 6.7). Postoperative administration of amiodarone reduced the occurrence of atrial fibrillation after elective CABG surgery, but was associated with a longer duration of cardiovascular instability and longer need for intensive care; magnesium prophylaxis had no effect. Advanced age and a low plasma magnesium concentration are risk factors for postoperative atrial fibrillation.

Status of selected nutrients and progression of human immunodeficiency virus type 1 infection

Immune function is highly dependent on nutritional status because the large mass and high rate of cellular turnover of the immune system make it a major user of nutrients. Furthermore, nutrient requirements may be increased during acute and chronic infections, including HIV-1 infection. The current study was designed to assess relations among HIV-1 progression and 11 nutritional and demographic variables. The participants were 106 HIV-infected outpatients and 29 uninfected control subjects (n = 89 men and 46 women; age range: 35-57 y). The HIV-infected subjects represented a broad range of disease progression. We found lower concentrations of plasma and erythrocyte magnesium and of erythrocyte reduced glutathione beginning early in the course of HIV-1 infection. Significantly decreased hematocrit and increased serum copper concentration developed only late in the course of the disease. Statistically significant univariate associations were found between the CD4(+) T lymphocyte count and hematocrit, plasma magnesium concentration, and plasma zinc concentration. The lowest erythrocyte magnesium concentrations occurred in HIV-infected subjects who consumed alcoholic beverages. Independent variables that were significant joint predictors of CD4(+) cell count in multiple regression analyses were hematocrit and plasma free choline and zinc concentrations. These 3 factors together explained 43% of the variability in CD4(+) cell counts. The results provide evidence that compromised nutritional and antioxidant status begin early in the course of HIV-1 infection and may contribute to disease progression.

Membrane, intracellular, and plasma magnesium and calcium concentrations in preeclampsia

Changes in intracellular calcium and magnesium concentrations seem to be involved in the pathogenesis of preeclampsia, whereas the role of cell membranes has not been studied in detail yet. To investigate the changes in calcium and magnesium metabolism in normal pregnancy and preeclampsia, plasma, intracellular, and membrane calcium and magnesium concentrations were determined in a clinical study. Twenty-five control, 18 untreated healthy pregnant, and 16 nulliparas preeclamptic women were investigated. Plasma, cellular, and membrane (erythrocytes) calcium and magnesium contents were measured by atomic absorption spectroscopy. Plasma and intracellular magnesium concentrations were significantly lower in the healthy pregnant group and the preeclamptic group as compared to controls ( P < .01). In erythrocyte membranes magnesium content was found significantly decreased in the preeclamptic women as compared to healthy subjects ( P < .001). There was a significant decrease in the plasma calcium concentration in the preeclamptic group compared to controls or healthy pregnant women ( P < .05). Membranous calcium content was significantly increased in the preeclamptic group versus controls or healthy pregnant women ( P < .001) and an inverse correlation with membranous magnesium content was found (r = −0.79, P < .01). Lowered plasma, intracellular, and membrane magnesium concentrations in preeclampsia may contribute to the development in hypertension in pregnancy. In addition, a disturbed calcium homeostasis is observed in preeclampsia.

Time courses of plasma magnesium concentrations and urinary magnesium excretion in cows subjected to acute changes in potassium intake

Hypomagnesaemic tetany in cows develops occasionally after an acute increase in K intake such as can occur when cows are transferred to spring grass. There is evidence that under these conditions plasma Mg concentrations are only transiently decreased. In this study the questions addressed were whether the plasma Mg concentration, indeed adapts to a high K intake as only dietary variable, and whether urinary Mg excretion is associated with this adaptation. Dry cows were fed rations containing either 26 or 50 g K/kg dm, the extra K being in the form of KHCO3. When the cows were acutely transferred from the low to the high K ration, plasma Mg concentrations fell slightly, but significantly from 0.86 to 0.76 mmo1/1 within five days, but rose again to 0.80 mmo1/1 after another 23 days, this rise being also statistically significant. None of the animals developed tetany. The decrease in plasma Mg concentration in individual animals after five days on the high‐K ration ranged from 6 to 21 %. The time course of urinary Mg excretion resembled that of plasma Mg concentration; minimum Mg excretion was seen after four to six days on the high‐K ration with a subsequent increase thereafter. To explain the transient lowering of plasma Mg concentration, it is suggested that the K‐induced decrease in Mg status caused a delayed increase in the carrier‐mediated component of Mg absorption, which in turn caused an increase in urinary Mg excretion. When the cows were acutely switched from the high to the low K ration, plasma Mg concentration and urinary Mg excretion rose, but no transient changes were seen.

In vivo effect of endothelin-1 on plasma calcium and parathyroid hormone concentrations.

We have previously reported an in vitro inhibitory effect of endothelin-1 (ET-1) on parathyroid hormone (PTH) secretion. In the present experiment, ET-1 was infused into rabbits to study the in vivo effect of ET-1 on the changes in calcium, magnesium, PTH and calcitonin concentrations. Femoral arteries and veins of anesthetized male rabbits were cannulated to monitor vital signs, blood sampling and infusion of the agents being studied. Infusion of ET-1 (1, 5, 10 and 20 ng/kg per min) induced a dose-dependent decline in plasma ionized calcium concentrations from 6.68+/-0.26 to 5.50+/-0.46 mg/dl (P<0.05) and a decrease in calcitonin concentrations from 48.6+/-6.5 to 32.5+/-4.7 pg/ml. PTH concentrations increased from 58.3+/-10.2 to 159.4+/-22.1 pg/ml. In a separate experiment, calcium gluconate solution was simultaneously infused to keep calcium concentrations steady, thereby proving a calcium 'clamp'. In normal calcium concentration, ET-1 infusion gradually decreased PTH concentrations from 71.4+/-8.6 to 38.0+/-6.2 pg/ml. We further infused sodium citrate solution to decrease the calcium concentration (2.0 mg/dl less) and calcium gluconate solution was infused to keep calcium concentrations steadily less than normal. PTH concentrations were initially stimulated by the induction of hypocalcemia (68.1+/-11.2 to 135.6+/-8.5 pg/ml), but decreased by ET-1 infusion (135.6+/-8.5 to 85.1+/-15.2 pg/ml). Plasma magnesium concentrations did not change significantly throughout the entire study and calcitonin concentrations were not significantly changed during the calcium clamp studies. Serum phosphate and 1,25-(OH)(2) vitamin D(3) concentrations were also measured, but they also did not change significantly. In conclusion, ET-1 exhibited an in vivo acute hypocalcemic action, independent of calcitonin. It also directly decreased PTH secretion if serum calcium concentrations were kept steady. The above findings are consistent with the results of our previous in vitro experiment.

A multivariate analysis for predicting cisplatin-induced delayed emesis.

The present study was designed to address the question of the early identification of patients at risk of developing cisplatin (CP)-related delayed emesis. This study included demographic, clinical, biological and pharmacological data and was conducted on 110 consecutive patients treated by CP-based chemotherapy. A previously validated single-point CP pharmacokinetic evaluation was performed in all patients. A total of 110 cycles was analyzed. Delayed vomiting (i.e., occurring between day 3 and day 7 following CP administration) was observed in 36.4% of cycles. Among the tested variables, the occurrence of delayed emesis was significantly related to elevated ultrafilterable (UF) platinum concentration (measured 16 h after the end of CP administration) and to low plasma magnesium concentration (measured 48 h before CP administration). Risk-thresholds for delayed emesis were established for UF platinum and magnesemia, at 60 ng/ml and 58 mmol/l, respectively. In the sub-group of patients with magnesemia determination, this later parameter was the only significant predictor of delayed emesis. Gender, cycle number, primary cancer location and age were not associated with the risk of developing delayed emesis. The ability to select patients at risk of delayed vomiting may offer a practical means of targeting administration of specific treatments.

Insulin-mediated glucose disposal is decreased in normal subjects with relatively low plasma magnesium concentrations

The relationship between the plasma magnesium (Mg) concentration and steady-state plasma insulin (SSPI) and glucose (SSPG) concentrations at the end of a 180-minute infusion of octreotide, insulin, and glucose was determined in 98 healthy nondiabetic subjects. For the purposes of data analysis, the population was divided into tertiles on the basis of the plasma Mg concentration: I, plasma Mg 0.83 mmol/L; II, plasma Mg 0.84 to 0.91 mmol/L; and III, plasma Mg 0.92 mmol/L. The three groups were identical in terms of age, gender distribution, and degree of obesity. However, both fasting plasma insulin (P < .05) and SSPG (P < .05) concentrations were significantly higher in the tertile (I) with the lowest plasma Mg concentration. Furthermore, there was a significant inverse correlation between plasma Mg and SSPG concentrations (r = -.27, P < .01) in the entire population. These results indicate that variations in the plasma Mg concentration have a relatively modest but significant effect on insulin-mediated glucose disposal in healthy subjects, with lower plasma Mg concentrations associated with increased insulin resistance.

Ventricular ectopic activity, left ventricular mass, hyperinsulinemia, and intracellular magnesium in normotensive patients with obesity.

Insulin resistance, a well-known feature of obesity, is associated with several pathological changes, which are potentially arrhythmogenic. Ventricular ectopic activity in normotensive obese patients has not been studied in detail. Therefore the authors designed a study to investigate potential relationships among ventricular ectopic activity, left ventricular mass, hyperinsulinemia, and intracellular magnesium concentration in obese patients. Thirty-two obese patients and 32 nonobese control subjects, who were referred to outpatient department because of ventricular ectopy, participated in the study. The groups were matched for age and gender. All had normal glucose tolerance. All subjects underwent a 75-g glucose tolerance test, and blood samples were obtained at 30, 60, and 120 minutes thereafter for determination of glucose and insulin concentrations. Echocardiography was performed and left ventricular mass index was calculated. The number of ventricular ectopic beats per hour (VEB/hour) was recorded by 24-hour ECG Holter monitoring. Plasma and erythrocyte magnesium concentrations were determined by atomic absorption spectrophotometer. Obese patients had higher body weight, body mass index, heart rate, and left ventricular mass index. Obese subjects had higher fasting insulin as well as insulin/glucose ratio and broader area under the curve of insulin (AUC-I) compared to nonobese subjects. Insulin sensitivity appeared to be lower in the obese group. Holter monitoring showed more VEB/hour in the obese group. Magnesium concentration in serum and in erythrocytes was lower in obese persons. In the obese group a positive correlation was found between left ventricular mass index and fasting insulin (r=0.345, p=0.027), insulin/glucose index (r=0.351, p=0.049), and AUC-I (r=0.405, p=0.011). The number of VEB/hour in obese patients was in positive correlation with age (r=0.681, p<0.001), left ventricular mass index (r=0.542, p=0.001), fasting insulin (r=0.380, p=0.016), and AUC-I (r=0.493, p=0.002) and in negative correlation with magnesium concentration in erythrocytes (r=-0.457, p=0.004). Multiple regression analysis showed that age and AUC-I are the only determinants of VEB/hour and together explained 56% of the variability in the obese subjects. It appears that in obese normotensive subjects, ventricular ectopic beats are related to age, insulin resistance, left ventricular mass index, and decreased intracellular magnesium content.

Antioxidant enzyme activities and trace element concentrations in ischemia-reperfusion.

In this study, we investigated the impact of ischemia-reperfusion on antioxidant enzyme activities and trace element concentrations. For this purpose, ischemia was initiated by clamping superior mesenteric artery of Wistar (albino) rats for 30 min, followed by reperfusion for 20 min. Immediately after reperfusion, blood samples were taken and examined for red cell copper-zinc superoxide dismutase (Cu-Zn-SOD), catalase (CAT), and glutathione peroxidase (GPx) activities spectrophotometrically and plasma zinc, copper, and magnesium concentrations by atomic absorption spectrophotometer. In the ischemia-reperfusion group, red cell Cu-Zn-SOD activity and plasma zinc and copper concentrations were increased significantly (p < 0.001) when compared to the control group; however, the increases in GPx activity and plasma magnesium concentration were not significant (p > 0.05). We also found a significant (p < 0.01) decrease in catalase activity. Free radicals released as a consequence of ischemia-reperfusion caused significant alterations in antioxidant enzymes and in the concentrations of trace elements.

Epithelial magnesium transport and regulation by the kidney

Magnesium is the fourth most abundant cation in the body and the second most common cation in the intracellular fluid. It is the kidney that provides the most sensitive control for magnesium balance. About a 80% of the total serum magnesium is ultrafilterable through the glomerular membrane. In all of the mammalian species studied to date, the proximal tubule of the adult animal reabsorbs only a small fraction, 10-15%, of the filtered magnesium. Unlike the adult proximal convoluted tubule that of young rats (aged 13-15 days) reabsorbs 50-60% of filtered magnesium along the proximal tubule together with sodium, calcium, and water. Micropuncture experiments, in every species studied to date, indicates that a large part (approximately 60%) of the filtered magnesium is reabsorbed in the loop of Henle. Magnesium reabsorption in the loop occurs within the cortical thick ascending limb (cTAL) by passive means driven by the transepithelial voltage through the paracellular pathway. Micropuncture experiments have clearly showed that the superficial distal tubule reabsorbs significant amounts of magnesium. Unlike the thick ascending limb of the loop of Henle, magnesium reabsorption in the distal tubule is transcellular and active in nature. Many hormones and nonhormonal factors influence renal magnesium reabsorption to variable extent in the cTAL and distal tubule. Moreover, nonhormonal factors may have important implications on hormonal controls of renal magnesium conservation. Dietary magnesium restriction leads to renal magnesium conservation with diminished urinary magnesium excretion. Adaptation of magnesium transport with dietary magnesium restriction occurs in both the cTAL and distal tubule. Elevation of plasma magnesium or calcium concentration inhibits magnesium and calcium reabsorption leading to hypermagnesiuria and hypercalciuria. The identification of an extracellular Ca2+/Mg2+ -sensing receptor located on the peritubular side of cTAL and distal tubule cells explains this phenomenon. Loop diuretics, such as furosemide and bumetanide, diminish salt absorption in the cTAL whereas the distally acting diuretics, amiloride and chlorothiazide stimulate magnesium reabsorption within the distal convoluted tubule. Finally, metabolic acidosis, potassium depletion or phosphate restriction can diminish magnesium reabsorption within the loop and distal tubule. Research in the 90's have greatly contributed to our understanding of renal magnesium handling.