When EGF is offside, magnesium is wasted.

Our understanding of magnesium (Mg(2+)) regulation has recently been catapulted forward by the discovery of several disease loci for monogenic disorders of Mg(2+) homeostasis. In this issue of the JCI, Groenestege et al. report that their study of a rare inherited Mg(2+) wasting disorder in consanguineous kindred shows that EGF acts as an autocrine/paracrine magnesiotropic hormone (see the related article beginning on page 2260). EGF stimulates Mg(2+) reabsorption in the renal distal convoluted tubule (DCT) via engagement of its receptor on the basolateral membrane of DCT cells and activation of the Mg(2+) channel TRPM6 (transient receptor potential cation channel, subfamily M, member 6) in the apical membrane. These authors show that a point mutation in pro-EGF retains EGF secretion to the apical but not the basolateral membrane, disrupting this cascade and causing renal Mg(2+) wasting. This work is another seminal example of the power of the study of monogenic disorders in the quest to understand human physiology.

Impaired basolateral sorting of pro-EGF causes isolated recessive renal hypomagnesemia.

Primary hypomagnesemia constitutes a rare heterogeneous group of disorders characterized by renal or intestinal magnesium (Mg(2+)) wasting resulting in generally shared symptoms of Mg(2+) depletion, such as tetany and generalized convulsions, and often including associated disturbances in calcium excretion. However, most of the genes involved in the physiology of Mg(2+) handling are unknown. Through the discovery of a mutation in the EGF gene in isolated autosomal recessive renal hypomagnesemia, we have, for what we believe is the first time, identified a magnesiotropic hormone crucial for total body Mg(2+) balance. The mutation leads to impaired basolateral sorting of pro-EGF. As a consequence, the renal EGFR is inadequately stimulated, resulting in insufficient activation of the epithelial Mg(2+) channel TRPM6 (transient receptor potential cation channel, subfamily M, member 6) and thereby Mg(2+) loss. Furthermore, we show that colorectal cancer patients treated with cetuximab, an antagonist of the EGFR, develop hypomagnesemia, emphasizing the significance of EGF in maintaining Mg(2+) balance.

Overexpression of HSP10 in skeletal muscle of transgenic mice prevents the age-related fall in maximum tetanic force generation and muscle Cross-Sectional Area.

Skeletal muscle atrophy and weakness are major contributors to frailty and impact significantly on quality of life of older people. Muscle aging is characterized by a loss of maximum tetanic force (P(o)) generation, primarily due to muscle atrophy, to which mitochondrial dysfunction is hypothesized to contribute. We hypothesized that lifelong overexpression of the mitochondrial heat shock protein (HSP) HSP10 in muscle of mice would protect against development of these deficits. P(o) generation by extensor digitorum longus muscles of adult and old wild-type and HSP10-overexpressing mice was determined in situ. Muscles were subjected to damaging lengthening contractions, and force generation was remeasured at 3 h or 28 days to examine susceptibility to, and recovery from, damage, respectively. Muscles of old wild-type mice had a 23% deficit in P(o) generation and a 10% deficit in muscle cross-sectional area compared with muscles of adult wild-type mice. Overexpression of HSP10 prevented this age-related fall in P(o) generation and reduction in cross-sectional area observed in muscles of old wild-type mice. Additionally, overexpression of HSP10 protected against contraction-induced damage independent of age but did not improve recovery if damage occurred. Preservation of muscle force generation and CSA by HSP10 overexpression was associated with protection against the age-related accumulation of protein carbonyls. Data demonstrate that development of age-related muscle weakness may not be inevitable and show, for the first time, that lifelong overexpression of an HSP prevents the age-related loss of P(o) generation. These findings support the hypothesis that mitochondrial dysfunction is involved in the development of age-related muscle deficits.

Intracellular calcium movements of frog skeletal muscle during recovery from tetanus.

Radioautographs of (45)Ca-labeled frog skeletal muscles have been prepared using freeze-dry and vapor fixation techniques to avoid displacement of the isotope during the preparation of the radioautographs. (45)Ca has been localized in resting muscles exposed to (45)Ca Ringer's for 5 min or 5 hr and in isotopically labeled muscles recovering from tetanic stimulation at room temperature or at 4 degrees C. In muscles soaked at rest for 5 min (45)Ca was present almost exclusively in the terminal cisternae. In all other muscles there were three sites at which the isotope was concentrated: (a) the terminal cisternae, (b) the intermediate cisternae and the longitudinal tubules, and (c) the A band portion of the myofibrils. The terminal cisternae were labeled more rapidly than the myofibrils, but both exchanges were accelerated by electrical stimulation. The amount of (45)Ca in the longitudinal tubules and the intermediate cisternae decreased with time after a tetanus as the amount in the terminal cisternae increased. It is proposed that electrical stimulation releases calcium from the terminal cisternae and that relaxation occurs from the binding of the released calcium by the longitudinal tubules and the intermediate cisternae. Complete recovery from mechanical activity involves the transport of this bound calcium into the reticulum and its subsequent binding by the terminal cisternae. Resting exchange of calcium occurs primarily between the terminal cisternae and the transverse tubules.

Effects of divalent cations on the time course of post-tetanic decay of miniature endplate potential frequency in frogs.

Relatively high external Mg2+ specifically induces a shoulder in the post-tetanic decay of miniature endplate potential frequency at frog neuromuscular junctions. This effect is antagonized by Ca2+, but not by Sr2+ and Mn2+. This shoulder formation is not caused by Mn2+ or dinitrophenol in the medium. It is suggested that Mg2+ enters nerve terminals and displaces Ca2+ from internal stores; Mg2+ subsequently interferes with Ca2+ removal until the Mg2+ itself has been removed. The dinitrophenol result suggests that ATP-dependent Ca2+ extrusion is not permanently slowed. An equally likely and simpler explanation is that Mg2+ enters nerve terminals and the Mg2+ itself causes an increase in miniature endplate potential frequency. External Ca2+ competes with Mg2+ for channel entry and prevents this effect. The time course of the decay of miniature endplate potential frequency reflects the processes involved in Mg2+ extrusion and/or uptake.

Neurotrophic factor mRNA expression in dentate gyrus is increased following in vivo stimulation of the angular bundle.

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are two structurally-related neurotrophins synthesized in dentate gyrus granule cells and pyramidal neurons of the hippocampal formation. These neurons receive excitatory glutamatergic afferents from the entorhinal cortex via the angular bundle/perforant path. In the present study, we tested whether electrophysiological stimulation of this glutamatergic pathway modifies NGF or BDNF messenger RNA (mRNA) expression in vivo. Within hours following brief trains of high frequency angular bundle stimulation, the levels of mRNA encoding both neurotrophins were increased exclusively in granule cells of the ipsilateral dentate gyrus. The increase in neurotrophic factor mRNA expression was found to be mediated through the N-methyl-D-aspartate (NMDA) glutamate receptor subtype, and occurred in the absence of seizure. These findings provide evidence that neurotrophic factor mRNA levels in the hippocampal formation are increased by direct activation of excitatory afferents originating in the entorhinal cortex. We suggest that the function of some neurotrophin-responsive neuronal populations may depend upon the integrity and activity of neurons in the entorhinal cortex, a population of neurons reported to be compromised in patients with Alzheimer's disease.

Oxidant production and immune response after stretch injury in skeletal muscle.

PURPOSE: This study investigated oxidant production and associated immune response after acute muscle stretch injury. METHODS: A standardized single stretch injury was performed on the tibialis anterior (TA) muscle of 36 male New Zealand white rabbits while contralateral control limbs underwent a sham surgery. Animals were sacrificed 0, 4, 12, 24, 48, and 72 h after injury. Potential sites of oxidant production, measured with a dichlorofluorescein (DCF) probe, were evaluated using two separate buffers. RESULTS: Nonmitochondrial oxidant production measured under basal buffer conditions (0.1 M potassium phosphate) was increased in both injured and control limbs at 24 h (P < 0.01) and was greater in the injured limb at 12 and 48 h (P < 0.01). There was also an interaction of time and injury (P < 0.05). Maximum oxidant production by neutrophils and macrophages, stimulated by the induced buffer (including 1.7 mM ADP, 0.1 mM NADPH, 0.1 mM FeCl3), was increased in both injured and control limbs at 4 h (P < 0.01) and was greater in the injured limb at 48 h (P < 0.01). Myeloperoxidase (MPO) activity, indicating the presence of activated neutrophils, was higher in the injured limb at 4 and 48 h (P < 0.01). The activities of superoxide radical producing and quenching enzymes, xanthine oxidase (XO) and superoxide dismutase (SOD), were elevated at 24 (P < 0.01) and 4 h (P < 0.05), respectively, but showed no difference between injured and control limbs. CONCLUSION: We conclude that acute muscle stretch injury and the required surgeries to generate the injury result in a biphasic increase in oxidant production in both injured and control limbs, suggesting a systemic immune response. The increase in oxidant production at 4 h may be caused by an increase in activated neutrophils, whereas XO activity may contribute to oxidant generation at 24 h.

Pathophysiological aspects of calcium metabolism in spasmophilia.

In order to clarify the pathophysiological mechanisms of spasmophilia, 34 subjects (31 females and 3 males) with spasmophilia were studied. The diagnosis of spasmophilia was based on a specific clinical protocol and electromyographic criteria. In the study, markedly reduced plasma ionized calcium and serum magnesium concentrations were observed together with slightly and non-significantly reduced plasma calcium and phosphate levels. An impairment of intestinal radiocalcium absorption was also noticed. Parathyroid secretion did not show any significant disturbance, but circulating calcitonin levels were found to be significantly lower than in normal subjects. The mean value of serum 25OHD was within the normal range, while a slight reduction in bone Gla protein, an index of osteoblastic activity, was detected. No difference between patients with spasmophilia and normal subjects was observed concerning 47Ca kinetics in red blood cells. The studies indicated that an impaired intestinal calcium transport together with low levels of circulating calcitonin represent the most important pathophysiological determinants of spasmophilia.

Vitamin D metabolites in spasmophilia.

The comparison of 20 untreated spasmophilic patients (2 men, 18 women) with 25 healthy subjects revealed no significant differences in vitamin D metabolite plasma levels or in other laboratory indexes of calcium metabolism except for ionized and cytosolic free calcium levels which were lower in the former group (P less than 0.01; P less than 0.001). After 3 months treatment with calcitonin and 25-hydroxyvitamin D there was a clear improvement in patient symptoms, no significant modification of 1,25-dihydroxyvitamin D levels and significant increases in 25-hydroxyvitamin D, cytosolic free calcium and urinary calcium (P less than 0.001, P less than 0.001 and P less than 0.01, respectively). We conclude that high plasma levels of 25-hydroxyvitamin D play an important role in restoring normal cytosolic free calcium levels and reducing clinical manifestations in spasmophilia.

Successful treatment of short stature and delayed puberty in congenital magnesium-losing kidney.

Bartter's syndrome is a well described but uncommon disease characterized by hypokalaemia and hyperplasia of the juxtaglomerular apparatus of the kidney. It may present in infancy with failure to thrive and muscle weakness; it commonly causes short stature. Lesions at different sites within the renal tubule have been proposed as the cause of the syndrome. However, the biochemical abnormalities in many cases can be explained by defective reabsorption of chloride in the ascending loop of Henle, with loss of sodium and water and a secondary increase in renin and aldosterone concentrations. Less severe cases have been described which present in adolescence and have tetany as a prominent feature. Primary renal loss of magnesium associated with potassium wasting has been described in such cases and it has been suggested that these can be distinguished from classical Bartter's syndrome by hypocalciuria. This less well characterized disease has been named Welt, Gitelman-Welt or Gitelman syndrome and may include deficient tubular reabsorption of chloride, but the sites of magnesium and potassium loss in the kidney are uncertain. We describe a patient with this syndrome who presented with short stature, delayed puberty and tetany and responded well to magnesium replacement.

Regional brain monoamine concentrations and their alterations in bovine hypomagnesaemic tetany experimentally induced by a magnesium-deficient diet.

Monoamines are important brain neurotransmitters. An investigation was carried out to determine if hypomagnesaemic tetany was associated with alterations in regional brain monoamine concentrations in bovines. The results, established in cows with normal magnesium status, demonstrated that regional differences existed in the distribution and concentration of brain monoamines in the adult bovine, which were similar to those in other species. In magnesium-deficient cows, severe hypomagnesaemia and lowered cerebrospinal fluid (CSF) magnesium concentrations were associated with significant alterations in monoamine concentrations in some brain regions. Alterations in 3,4-dihydroxyphenylalanine (DOPA) and dihydroxyphenylacetic acid (DOPAC) concentrations in the corpus striatum, and dopamine (DA) in the cerebral cortex and cerebellum were recorded. These regions play an important role in both voluntary and involuntary motor function, and therefore these alterations may play a role in the aetiology of hypomagnesaemic tetany. However, there was no significant change in DA concentrations in the corpus striatum (the main dopaminergic region in the brain) associated with hypomagnesaemia. In addition, a significantly lower norepinephrine (NE) concentration in the corpus striatum of hypomagnesaemic animals was also recorded. Norephinephrine is generally excitatory and therefore lowered NE concentrations would be expected to result in depression rather than stimulation of motor function.

Wheat pasture poisoning. II. Tissue composition of cattle grazing cereal forages and related to tetany.

Thirty-two aged Hereford and Angus cows (avg 10.2 yr old) grazed mixed cereal (wheat and rye) pastures from December 6, 1979 to April 23, 1980 (138 d). On d 104 (March 19), five cows developed tetany. On the day of tetany, the mean plasma Ca of the cows with tetany was 4.1 mg/dl. Cows with tetany had plasma Mg concentrations of 1.7 mg/dl on the day of tetany, but 15 d before tetany and 6 d post-tetany, levels were lower (1.2 mg/dl). Cows with tetany had large increases in plasma parathyroid hormone (PHT) as well as vitamin 1, 25 dihydroxy D3 [1,25(OH)2D], plasma glucose, lactic acid and beta-hydroxybutyric acid. Plasma K of these cows followed a similar trend as plant K, except it was not as pronounced. Plasma inorganic P of these same cows was exceedingly low, less than 3 mg/dl several times, although the forage P did not indicate a P deficiency. Levels of plasma hydroxyproline in these cows indicated that bone resorption may have been low during most of the grazing season, even though levels of plasma hydroxyproline were initially high and high subsequent to tetany. High levels of plasma glucose and lactic acid were associated with the time of tetany. Apparently, cows developed inappetence around the time of tetany, as suggested by the high levels of plasma beta-hydroxybutyric acid. Cows with wheat pasture poisoning appeared to respond to the severe hypocalcemia with large increases in plasma 1,25(OH)2D. Plasma 1,25(OH)2D changes were similar to plasma hydroxyproline changes (and possible bone resorption rates) and seemed inversely proportional to plasma Ca and directly proportional to plasma PTH concentrations. Generally, cerebrospinal fluid (CSF) composition was not affected as much as plasma composition, except for the low levels of CSF Ca. These data indicate that a metabolic deficiency of Ca (hypocalcemia) was the cause of tetany.

[Mitral valve prolapse and spasmophilia in the adult]. / Prolapsus valvulaire mitral et spasmophilie chez l'adulte.

75 cases of mitral valve prolapse (MVP) for which no cause was found underwent electromyography (EMG). In 64 cases (85.3%) EMG showed changes suggestive of spasmophilia. The symptoms observed were those already described in this condition. The specific clinical signs of spasmophilia were often elicited with a positive Chvostek sign in 20 out of 30 cases (73.3%). Radiological, echocardiographical and haemodynamic studies underlined the hyperkinetic state of the left ventricle. Biochemical investigations showed a high incidence of low erythrocytic magnesium levels. Chest pain suggestive of angina pectoris, mitral valve prolapse and spasmophilia are frequently associated. The role of the low erythrocyte magnesium on left ventricular hyperkinesis and the production of MVP is discussed.

Hypomagnesaemia and new data on vitreous humour magnesium concentration as a post-mortem marker in ruminants.

Magnesium deficit has been associated with many sub-clinical and clinical conditions in humans and animals. The incidence of hypomagnesaemia is high in lactating cows grazing spring pastures, occasionally resulting in the often fatal condition known as grass tetany. While plasma magnesium concentrations can be used to assess magnesium status in the live animal, post-mortem diagnosis of clinical grass tetany is difficult. Recent studies have investigated the potential of eye fluid magnesium concentration as a post-mortem marker of hypomagnesaemic tetany. In tetany induction studies carried out in adult ewes and lactating cows significant relationships were found to exist between the concentrations of magnesium in either cerebrospinal fluid or plasma and either aqueous or vitreous humour. In freshly dead animals aqueous humour magnesium concentrations of < 0.33 mmol/L in adult sheep and < 0.25 mmol/L in adult cattle were associated with severe hypomagnesaemia and tetany. However, aqueous humour was found to be unstable post-mortem. Vitreous humour was considerably more stable and a vitreous humour magnesium concentration in adult sheep of < 0.65 mmol/L for up to 24 hours post-mortem or < 0.55 mmol/L in adult cows for up to 48 hours was associated with severe hypomagnesaemia and tetany. Provided clear-fluid samples are taken from appropriate animals and processed correctly in the laboratory, the concentration of magnesium in vitreous humour is a useful and practical marker in the post-mortem diagnosis of hypomagnesaemic tetany in ruminants.

Transient cerebral ischaemic attacks and calcium-magnesium imbalance: clinical and paraclinical findings in 106 patients under 50 years of age.

One hundred and six selected patients (71 women, 35 men) suffering from transient cerebral ischaemic attacks (TIA) when aged less than 50 years received a comprehensive diagnostic assessment. Patients were classified into three subgroups, into which 9% could be assigned in approximately equal proportions. These were group A; TIA patients with tetanic syndrome (median age of first TIA 32 years, mainly female, 3.2 attacks per year and changing vascular area); group B; TIA patients with migraine (median age of first TIA 26 years, no predominance of male or female sex, 2.0 attacks per year and mostly in the same vascular area); group C: TIA patients suffering from premature arteriosclerosis (median age of first TIA 40 years, no predominance of male or female sex. 0.8 attacks per year and mostly in the same vascular area). Magnesium (P less than 0.001) and calcium (P less than 0.05) in plasma were reduced in group A, and magnesium (P less than 0.05) in group B, versus group C. The increased propensity to vasoconstriction appears to be an important pathogenic factor, particularly in group A, but also in group B.

[Magnesium balance in patients with spasmophilia. Relation to results of electromyography]. / Magneziová bilance u nemocných se spazmofilií. Vztah k výsledkum elektromyografie.

BACKGROUND: The pathophysiological basis of spasmophilia is frequently magnesium deficiency and the therapeutic administration of magnesium salts has usually a favourable effect. However the parameters of magnesium balance are not always consistent with the results of electromyography. The objective of the present work was to test and interpret the relationship of results of these two basic diagnostic procedures indicated when spasmophilia is suspected. METHODS AND RESULTS: Thirty-three subjects (9 men and 24 women) with suspected spasmophilia were examined by non-invasive electromyography, using the technique of surface electrodes. All subjects had concurrently biochemical examinations: serum calcium and ionized calcium, serum magnesium (S-mg), magnesium in erythrocytes (ery-Mg) and magnesium in the blood haemolysate (H-Mg). In 29 patients and oral magnesium loading test was made with evaluation of the urinary Mg excretion after a constant Mg load (U-Mg). Statistical evaluation of the investigated parameters of the magnesium balance revealed a highly significant relationship between ery-Mg and U-Mg and H-Mg and ery-Mg (p < 0.005). A less close relationship was found between H-Mg and S-Mg (p < 0.05). Total and ionized calcium was in all examined subjects within the range of the arbitrary normal range. The EMG finding was positive (the finding of two and more multiplets in the ischaemic and hyperventilation test resp.) in 30 instances, i.e. in 91% of the examined subjects. In 72% there was agreement of the positivity of the EMG and magnesium deficiency (i.e. reduced values of ery-Mg and U-Mg), positivity of EMG combined with normal parameters of the Mg balance was recorded in 18%. In 6.1% of the examined subjects magnesium deficiency was confirmed combined with a normal EMG finding. CONCLUSIONS: Concurrent positivity of EMG and magnesium deficiency in 72% justifies the therapeutic administration of magnesium. In patients with a normal magnesium deficiency and positive EMG another cause of spasmophilia must be taken into consideration, incl. technical errors of interpretation of EMG results. A negative EMG associated with magnesium deficiency can suggest the central form of tetany, where magnesium treatment is also unequivocally indicated.

[Treatment of patients with gastrogenic tetany]. / Lechenie bol'nykh s gastrogennoi tetaniei.

The article analyses the results of combined treatment of 22 patients with duodenal ulcer complicated by cicatricial-ulcerative obstruction of the pylorus, gastrogenic tetany. Within 9-11 days of intensive therapy, the disorders of homeostasis were stopped and operation was performed for restoring the passage of food. Combined treatment reduced the mortality from 30 to 13% among this category of patients.

[Electrophysiological analysis of functional state of spinal cord motoneurons in rats with parathyroprivous tetany].

In normal rats and of those with parathyroprivous (hypocalcemic) tetany the comparative analysis of background activity (BA), tetanic and posttetanic increase and decrease of frequency of spinal cord (SC) motoneurons (MNs) responses under high-frequency (50, 100Hz) stimulation (HFS) of flexor (G) and extensor (P) hind-limb nerves have been conducted. The on-line selection and program analysis of the spikes was produced. On the 3-7 and 21-22 days of development of acute and chronic tetany, respectively, the significant tetanic and posttetanic changes of MNs activity without meaningful changes in BA was registered. Along with the abrupt increase of excitatory manifestation of activity to HFS in a period of development of acute tetany was observed their relative weakening in animals with chronic tetany. Simultaneously the weakening or total disappearance of depressor reaction, especially expressed in the period of development of acute tetany was noted. It was concluded on the causal dependence of the parathyroprivous convulsions due to disturbances of correlation of inhibitory-excitatory processes in SC MNs.

Calcium and magnesium physiology and nutrition in relation to the prevention of milk fever and tetany (dietary management of macrominerals in preventing disease).

Dairy cows may suffer events of hypocalcemia and hypomagnesemia, commonly known as milk fever and tetany. Milk fever is characterized by hypocalcemia at parturition as a consequence of a sudden increase in Ca demand and an unavoidable delay in Ca metabolism adaptation. Tetany is due to impaired Mg absorption from the rumen that cannot be compensated by absorptive or excretory adaptation, resulting in a net nutritional shortage of Mg and culminating in hypomagnesemia. Prevention strategies require triggering the activation of Ca gastrointestinal absorption and avoiding factors limiting ruminal Mg absorption.