Correlation between magnesium and potassium contents in muscle: role of Na(+)-K+ pump

Magnesium in hypertension: mechanisms and clinical implications

Hypertension is associated with increased risk of cardiovascular disease and death. Evidence suggests that Mg2+ depletion contributes to hypertension. It is estimated that 25% or more of the United States population experiences chronic, latent Mg2+ depletion. This review explores mechanisms by which Mg2+ influences blood pressure, modifying risk of hypertension and complicating its treatment. Mechanisms addressed include effects upon i) sympathetic tone, via the modulation of N-methyl-D-aspartate (NMDA) receptor and N-type Ca2+ channel activity, influencing catecholamine release from sympathetic nerve endings; ii) vascular tone, via alteration of L-type Ca2+ and endothelial nitric oxide synthase (eNOS) activity and prostacyclin release; iii) renal K+ handling, influencing systemic K+ balance and potentially indirectly influencing blood pressure; iv) aldosterone secretion from the adrenal cortex; and v) modulation of pro-hypertensive inflammatory processes in dendritic cells and macrophages, including activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome and stimulation of isolevuglandin (IsoLG) production. Discovery of these mechanisms has furthered our understanding of the pathogenesis of hypertension, with implications for treatment and has highlighted the role of Mg2+ balance in hypertension and cardiovascular disease.

Serum Magnesium Levels in Preterm Infants Are Higher Than Adult Levels: A Systematic Literature Review and Meta-Analysis

Magnesium (Mg) is an essential mineral in the body, impacting the synthesis of biomacromolecules, bone matrix development, energy production, as well as heart, nerve, and muscle function. Although the importance of Mg is evident, reference values for serum Mg (sMg) in pediatric patients (more specifically, in neonates) are not well established. This systematic literature review and meta-analysis (using 47 eligible studies) aims to quantify normal and tolerable ranges of sMg concentrations during the neonatal period and to highlight the factors influencing Mg levels and the importance of regulating sMg levels during pregnancy and birth. In newborns without Mg supplementation during pregnancy, magnesium levels at birth (0.76 (95% CI: 0.52, 0.99) mmol/L) were similar to that of mothers during pregnancy (0.74 (95% CI: 0.43, 1.04) mmol/L), but increased during the first week of life (0.91 (95% CI: 0.55, 1.26) mmol/L) before returning to adult levels. This pattern was also seen in newborns with Mg supplementation during pregnancy, where the average was 1.29 (95% CI: 0.50, 2.08) mmol/L at birth and 1.44 (95% CI: 0.61, 2.27) mmol/L during the first week of life. Factors influencing these levels include prenatal Mg supplementation, gestational age, birth weight, renal maturity/function, and postnatal Mg intake. Elevated Mg levels (>2.5 mmol/L) have been associated with an increased risk of mortality, admission into intensive care, hypotonia, hypotension, and respiratory depression but sMg concentrations up to 2.0 mmol/L appear to be well tolerated in neonates, requiring adequate survey and minimal intervention.

Analysis of six elements (Ca, Mg, Fe, Zn, Cu, and Mn) in several wild vegetables and evaluation of their intakes based on Korea National Health and Nutrition Examination Survey 2010-2011

Wild vegetables, those edible among naturally grown vegetables, have been reported to contain many bioactive substances, dietary fibers, vitamins, and minerals. The purpose of this study is to examine the six elements of the wild vegetables frequently consumed by Koreans and assess the element intakes through them. Contents of six kinds of elements (Ca, Mg, Fe, Zn, Cu, and Mn) in 11 wild vegetables were analyzed by inductively coupled plasma optical emission spectroscopy. Using these analysis data, the 6-element intakes from the wild vegetables were evaluated in healthy Korean adults aged 19-64 years from the Korea National Health and Nutrition Examination Survey (2010-2011). Sedum and shepherd's purse contained over 100 mg of Ca in 100 g of their edible portion. The Mg content per 100 g of the 11 wild vegetables ranged from 12.1 mg to 43.4 mg. The wild vegetable with the highest mineral content per 100 g was sedum for Ca, spinach for Mg, shepherd's purse for Fe, spinach for Zn, bracken for Cu, and fragrant edible wild aster for Mn. The element intakes from the 11 wild vegetables compared with dietary reference intakes in the healthy Koreans were 1.0 % for Ca, 2.1 % for Mg, 5.3 % for Fe, 1.4 % for Zn, 0.3 % for Cu, and 1.8 % for Mn. Considering the low intake ratio (1.2 %) of the wild vegetable to total food intake, wild vegetables may contribute to some element intakes. Our results show the nutritional value of the wild vegetables in the aspect of mineral nutrition; however, further research is needed to evaluate the bioavailability of various elements in wild vegetables.

Bartter syndrome and growth hormone deficiency: three cases

BACKGROUND

Bartter syndrome is a rare autosomal recessive disorder characterized by hypokalemia, salt loss, and metabolic alkalosis. Short stature is one of the clinical manifestations in these children. Although polyuria, polydipsia, hypokalemia, and salt loss may be responsible for growth retardation, the exact pathogenesis of short stature in Bartter syndrome is not known.

CASE DIAGNOSIS AND TREATMENT

In this study, we present three children diagnosed as having Bartter syndrome with short stature and growth hormone (GH) deficiency. After recombinant human growth hormone therapy (rhGH), their growth velocities were improved.

CONCLUSIONS

These results indicate that GH deficiency may contribute to short stature in children with Bartter syndrome, and rhGH therapy would be an excellent adjunctive treatment for short children with this syndrome whose condition is resistant to conventional therapies in terms of growth.

Longitudinal growth in chronic hypokalemic disorders

Growth retardation remains a major complication in children with primary tubular disorders, despite adequate supplemental treatment with electrolytes, water and bicarbonate. Chronic hypokalemia, characteristic of some tubulopathies, impairs growth by mechanisms that are not well known. Association with growth hormone deficiency has been reported in patients with Bartter's or Gitelman's syndrome. Tissue-specific alterations of growth hormone and insulin-like growth factor I axis have been described in experimental models of potassium depletion. Hypokalemic rats gain less body length and weight than pair-fed normokalemic animals and, by contrast, develop renal hypertrophy. These rats have low circulating concentrations of insulin-like growth factor I, depressed messenger ribonucleic acid (mRNA) levels of this peptide in the tibial growth plate, and they are resistant to the longitudinal growth-promoting effects of exogenous growth hormone. The reason for this resistance remains to be defined. No alterations in the intracellular signaling for growth hormone have been found in the liver of hypokalemic rats. However, treatment with high doses of growth hormone is unable to normalize hypertrophy of the epiphyseal cartilage chondrocytes, which are severely disturbed in potassium depletion and likely play an important role in the pathogenia of growth impairment in this condition.

Proposed Recommended Nutrient Densities for Moderately Malnourished Children

Recommended Nutrient Intakes (RNIs) are set for healthy individuals living in clean environments. There are no generally accepted RNIs for those with moderate malnutrition, wasting, and stunting, who live in poor environments. Two sets of recommendations are made for the dietary intake of 30 essential nutrients in children with moderate malnutrition who require accelerated growth to regain normality: first, for those moderately malnourished children who will receive specially formulated foods and diets; and second, for those who are to take mixtures of locally available foods over a longer term to treat or prevent moderate stunting and wasting. Because of the change in definition of severe malnutrition, much of the older literature is pertinent to the moderately wasted or stunted child. A factorial approach has been used in deriving the recommendations for both functional, protective nutrients (type I) and growth nutrients (type II).

K+, Na+, Mg2+, Ca2+, and water contents in human skeletal muscle: correlations among these monovalent and divalent cations and their alterations in K+ -depleted subjects

None of previous studies had simultaneously analyzed the K(+), Na(+), Mg(2+), and Ca(2+) contents in human skeletal muscle. We examined extensively and simultaneously the levels of all these cations and examined water content in vastus lateralis and pectoralis major muscles in 30 northeastern Thai men who were apparently healthy but died from an accident. Specimen collection was performed within 6 h of death. We used atomic absorption or flame photometry to measure the level of muscle cation. Histopathology of muscle and kidney was also evaluated. K(+), Na(+), Mg(2+), and Ca(2+) contents in vastus lateralis were 84.74 +/- 1.50, 38.64 +/- 0.77, 7.58 +/- 0.17, and 0.94 +/- 0.06 micromol/g wet weight, respectively, whereas K(+), Na(+), and Mg(2+) contents in pectoralis major were 82.83 +/- 1.54, 37.57 +/- 0.72, and 7.30 +/- 0.17 micromol/g wet weight, respectively. The water component was comparable in vastus lateralis and pectoralis major (78.66 +/- 0.41 and 78.09 +/- 0.56 %, respectively). Based on muscle K(+) levels, we divided the subjects into 2 main groups: K(+)-depleted (KD) group (K(+) < 80 micromol/g wet weight; n = 7) and non-K(+)-depleted (NKD) group (K(+) > or = 80 micromol/g wet weight; n = 23). In the KD muscle, Na(+) and Ca(2+) levels were significantly higher, whereas the level of Mg(2+) was significantly lower. Linear regression analysis showed significant correlations of K(+) and Mg(2+) levels and between Na(+) and Ca(2+). However, K(+) and Mg(2+) had the negative correlation with Na(+) and Ca(2+). Histopathologic examination showed no change in the KD muscles, whereas 29% (2 of 7) of the KD kidneys had vacuolization in proximal renal tubular cells. Our study not only provided the descriptive data but also implied the balance or homeostasis of these monovalent and divalent cations in their muscle pools.

Magnesium supplementation and muscle function in patients with alcoholic liver disease: a randomized, placebo-controlled trial

OBJECTIVE

The study was undertaken in order to evaluate the effect of magnesium (Mg) supplementation on muscle contents of Mg, muscle strength, muscle mass and sodium, potassium pumps (Na,K-pumps) in patients with alcoholic liver disease. Retrospectively, patients were also stratified according to spironolactone treatment.

MATERIAL AND METHODS

The study comprised a placebo-controlled, randomized trial in which 59 consecutive patients with alcoholic liver disease were treated with Mg intravenously and orally (12.5 mmol daily) or placebo for 6 weeks. Muscle content of Mg, maximum isokinetic muscle strength, skeletal muscle mass and muscle content of Na,K-pumps were measured before and after Mg supplementation.

RESULTS

Muscle Mg did not increase during the trial (paired t-test), but Mg supplementation and the duration of pre-study spironolactone treatment were independent predictors of muscle Mg (multiple regression). Muscle strength increased by 14% during the trial (p<0.001) and muscle mass increased by 11% (p=0.05), but with no difference between placebo and Mg treatment. Spironolactone treatment was associated with a 33% increase in the content of Na,K-pumps (p<0.001).

CONCLUSIONS

Six weeks of Mg supplementation did not increase muscle Mg, although Mg supplementation and spironolactone treatment were independent predictors of muscle Mg. The intervention had no effect on muscle strength and mass, but both increased during the study, probably owing to the general care and attendance to the patients.

Potassium depletion improves myocardial potassium uptake in vivo

Potassium depletion (KD) is a very common clinical entity often associated with adverse cardiac effects. KD is generally considered to reduce muscular Na-K-ATPase density and secondarily reduce K uptake capacity. In KD rats we evaluated myocardial Na-K-ATPase density, ion content, and myocardial K reuptake. KD for 2 wk reduced plasma K to 1.8 +/- 0.1 vs. 3.5 +/- 0.2 mM in controls (P < 0.01, n = 7), myocardial K to 80 +/- 1 vs. 86 +/- 1 micromol/g wet wt (P < 0.05, n = 7), increased Mg, and induced a tendency to increased Na. Myocardial Na-K-ATPase alpha(2)-subunit abundance was reduced by approximately 30%, whereas increases in alpha(1)- and K-dependent pNPPase activity of 24% (n = 6) and 13% (n = 6), respectively, were seen. This indicates an overall upregulation of the myocardial Na-K pump pool. KD rats tolerated a higher intravenous KCl dose. KCl infusion until animals died increased myocardial K by 34% in KD rats and 18% in controls (P < 0.05, n = 6 for both) but did not induce different net K uptake rates between groups. However, clamping plasma K at approximately 5.5 mM by KCl infusion caused a higher net K uptake rate in KD rats (0.22 +/- 0.04 vs. 0.10 +/- 0.03 micromol x g wet wt(-1) x min(-1); P < 0.05, n = 8). In conclusion, a minor KD-induced decrease in myocardial K increased Na-K pump density and in vivo increased K tolerance and net myocardial K uptake rate during K repletion. Thus the heart is protected from major K losses and accumulates considerable amounts of K during exposure to high plasma K. This is of clinical interest, because a therapeutically induced rise in myocardial K may affect contractility and impulse generation-propagation and may attenuate increased myocardial Na, the hallmark of heart failure.

Potassium depletion increases potassium clearance capacity in skeletal muscles in vivo during acute repletion

Muscular K uptake depends on skeletal muscle Na-K-ATPase concentration and activity. Reduced K uptake is observed in vitro in K-depleted rats. We evaluated skeletal muscle K clearance capacity in vivo in rats K depleted for 14 days. [(3)H]ouabain binding, alpha(1) and alpha(2) Na-K-ATPase isoform abundance, and K, Na, and Mg content were measured in skeletal muscles. Skeletal muscle K, Na, and Mg and plasma K were measured in relation to intravenous KCl infusion that continued until animals died, i.e., maximum KCl dose was administered. In soleus, extensor digitorum longus (EDL), and gastrocnemius muscles K depletion significantly reduced K content by 18%, 15%, and 19%, [(3)H]ouabain binding by 36%, 41%, and 68%, and alpha(2) isoform abundance by 34%, 44%, and 70%, respectively. No significant change was observed in alpha(1) isoform abundance. In EDL and gastrocnemius muscles K depletion significantly increased Na (48% and 59%) and Mg (10% and 17%) content, but only tendencies to increase were observed in soleus muscle. K-depleted rats tolerated up to a fourfold higher KCl dose. This was associated with a reduced rate of increase in plasma K and increases in soleus, EDL, and gastrocnemius muscle K of 56%, 42%, and 41%, respectively, but only tendencies to increase in controls. However, whereas K uptake was highest in K-depleted animals, the K uptake rate was highest in controls. In vivo K depletion is associated with markedly increased K tolerance and K clearance despite significantly reduced skeletal muscle Na-K-ATPase concentration. The concern of an increased risk for K intoxication during K repletion seems unwarranted.

Muscle strength, Na,K-pumps, magnesium and potassium in patients with alcoholic liver cirrhosis -- relation to spironolactone

OBJECTIVES

To evaluate the muscle strength in relation to muscle contents of magnesium (Mg), potassium (K) and sodium, potassium (Na,K)-pumps in patients with alcoholic cirrhosis.

DESIGN

An open cross-sectional study.

SETTING AND SUBJECTS

Fifty-one consecutive patients with liver cirrhosis admitted to the Department of Hepatology, Aarhus University Hospital, Denmark, and 28 age- and sex-matched healthy control subjects.

MAIN OUTCOME MEASURES

Biopsies of skeletal muscle were performed in patients and controls for measurements of Mg, K, and Na,K-pumps. Furthermore, maximum isokinetic knee extension and skeletal muscle mass were evaluated.

RESULTS

Muscle mass, muscle strength, muscle Mg and muscle K were substantially reduced in the patients (P < 0.01, all), and fell with increasing severity of the liver disease reflected in the Child-Pugh (C-P) class. Patients treated with spironolactone for 2 weeks or more, had increased muscle strength, muscle Mg and content of Na,K-pumps, compared with the rest of the patients (P < 0.05, all). In a multivariate analysis of the patients, skeletal muscle mass, muscle Mg and daily alcohol consumption (g) were independent predictors of isokinetic muscle strength (P < 0.05, all).

CONCLUSIONS

Patients with alcoholic liver cirrhosis showed considerably reduced muscle strength and muscle Mg was an independent predictor of muscle strength. Surprisingly, in the spironolactone treated patients, muscle weakness was less pronounced, possibly because of the action of spironolactone on muscle Mg, K and Na,K-pump content.

Dynamics and consequences of potassium shifts in skeletal muscle and heart during exercise

Since it became clear that K(+) shifts with exercise are extensive and can cause more than a doubling of the extracellular [K(+)] ([K(+)](s)) as reviewed here, it has been suggested that these shifts may cause fatigue through the effect on muscle excitability and action potentials (AP). The cause of the K(+) shifts is a transient or long-lasting mismatch between outward repolarizing K(+) currents and K(+) influx carried by the Na(+)-K(+) pump. Several factors modify the effect of raised [K(+)](s) during exercise on membrane potential (E(m)) and force production. 1) Membrane conductance to K(+) is variable and controlled by various K(+) channels. Low relative K(+) conductance will reduce the contribution of [K(+)](s) to the E(m). In addition, high Cl(-) conductance may stabilize the E(m) during brief periods of large K(+) shifts. 2) The Na(+)-K(+) pump contributes with a hyperpolarizing current. 3) Cell swelling accompanies muscle contractions especially in fast-twitch muscle, although little in the heart. This will contribute considerably to the lowering of intracellular [K(+)] ([K(+)](c)) and will attenuate the exercise-induced rise of intracellular [Na(+)] ([Na(+)](c)). 4) The rise of [Na(+)](c) is sufficient to activate the Na(+)-K(+) pump to completely compensate increased K(+) release in the heart, yet not in skeletal muscle. In skeletal muscle there is strong evidence for control of pump activity not only through hormones, but through a hitherto unidentified mechanism. 5) Ionic shifts within the skeletal muscle t tubules and in the heart in extracellular clefts may markedly affect excitation-contraction coupling. 6) Age and state of training together with nutritional state modify muscle K(+) content and the abundance of Na(+)-K(+) pumps. We conclude that despite modifying factors coming into play during muscle activity, the K(+) shifts with high-intensity exercise may contribute substantially to fatigue in skeletal muscle, whereas in the heart, except during ischemia, the K(+) balance is controlled much more effectively.

Optimal nutrition: calcium, magnesium and phosphorus

In the past, a major challenge for nutrition research was in defining indicators of nutritional adequacy. More recently, the research base related to the role of nutrition in chronic disease has expanded sufficiently to permit moving beyond deficiency indicators to other indicators with broader functional significance. Thus, nutrition research is faced with the new challenge of defining 'optimal nutrition'. One definition of optimal nutrition with respect to any particular nutrient could be when a functional marker reaches an 'optimal value' or plateau beyond which it is not longer affected by intake or stores of the nutrient. A functional marker of nutrient status could be defined as a physiological or biochemical factor which (1) is related to function or effect of the nutrient in target tissue(s) and (2) is affected by dietary intake or stores of the nutrient (which may include markers of disease risk). Examples of such indicators or markers are those related to risk of chronic diseases such as osteoporosis, CHD, or hypertension. The present review focuses on the concept of optimal nutrition with respect to three nutrients, Ca, Mg and P. However, for P and Mg there are as yet no functional indicators which respond to dietary intake, and in such cases nutrient requirements are established using more traditional approaches, e.g. balance data. For Ca, there has been interest in using maximal Ca retention, which is based on balance data, bone mass measurements and biomarkers of bone turnover as useful functional indicators of the adequacy of Ca intake.

Nutritional support in malnourished paediatric patients

An imbalance between a person's energy requirements and his or her dietary protein and caloric supply is the source of protein energy malnutrition (PEM), which compounds the problems of any underlying disease. Malnutrition may occur quite rapidly in critically ill patients, particularly those suffering from sepsis, setting up a vicious cycle with worsening of the PEM. This chapter examines the main consequences of PEM, the means whereby appropriate nutrition may be provided, and risks for severely malnourished paediatric patients in hospital. If the gastrointestinal tract can be used for refeeding, it should be used. When the gastrointestinal tract is unable to meet the protein and energy requirements, parenteral nutrition (PN) is required. PN is efficient but carries a high risk of metabolic complications known as the refeeding syndrome and directly related to the homeostatic changes secondary to severe PEM. Catch-up growth may be achieved by using appropriate nutritional support. Changes in body composition have to be assessed during the course of renutrition.

Oral rehydration solution in the year 2000: pathophysiology, efficacy and effectiveness

The use of oral rehydration solution (ORS) with early refeeding forms the basis of therapy for dehydration secondary to diarrhoea ORS has produced such positive results in dehydrated patients that no further scientific demonstration is needed to confirm its efficacy. This review presents several issues that remain unsettled or controversial. They include the following. 1. The mechanism of water handling by the intestine is discussed; this is more complex than initially thought, at the epithelial, cellular and molecular level. 2. The composition of ORS which has been successfully adapted for the most frequent conditions, except for severely malnourished children, is described. 3. In contrast to the strong scientific basis and obvious efficacy in rehydration of ORS, its consequences for growth, nutrition and mortality are difficult to demonstrate, unless adequate long-term nutritional support is also provided in addition to ORS. 4. Finally, discrepancies between the recommendations and the practice of oral rehydration therapy are now well documented. Analysis of the causes of these discrepancies may participate in improving public health campaigns.

Control of thymus physiology by peptidic hormones and neuropeptides

Several immune-neuroendocrine interactions are known to occur both in primary and secondary lymphoid organs. Here, Mireille Dardenne and Wilson Savino review data obtained in humans and experimental animals showing that peptidic hormones and neuropeptides can influence the thymus pleiotropically. These mediators modulate thymic epithelial cells (TECs), affecting thymulin secretion, cytokeratin expression, production of extracellular matrix (ECM) proteins and cell growth. Interestingly, such neuroendocrine influences appear to be part of a bidirectional circuitry, since thymic-derived peptides also regulate the release of hormones from the pituitary and hypothalamus.

Oral magnesium supplementation restores the concentrations of magnesium, potassium and sodium-potassium pumps in skeletal muscle of patients receiving diuretic treatment

In 76 consecutive patients who had received diuretics for 1-17 years for arterial hypertension or congestive heart failure, muscle concentrations of magnesium, potassium, and sodium-potassium pumps were significantly reduced compared to 31 age- and sex-matched controls. Thirty-six patients with muscle magnesium and/or potassium below the control level received oral magnesium hydroxide supplement for 2-12 weeks (n = 20) or 26 weeks (n = 16). After short-term (2-12 weeks) magnesium supplementation muscle parameters were increased, but far from normalized. After magnesium supplementation for 26 weeks, the muscle concentrations of magnesium, potassium and sodium-potassium pumps were normalized in most cases. Oral magnesium supplementation may restore diuretic-induced disturbances in the concentrations of magnesium, potassium and sodium potassium pumps in skeletal muscle. A supplemental period of at least 6 months seems to be required before complete normalization can be expected.