DIETARY MAGNESIUM DEFICIENCY INCREASES LEVELS AND FUNCTION OF Giα IN THE RAT HEART AFTER MYOCARDIAL INFARCTION

Magnesium(Mg) is crucial for the function of G proteins which play important roles in mediating the inotropic effects of β adrenergic agonists in the heart and are alteredin heart failure.This study was performed to determine whether or not dietary Mg deficiency alters functional activity and levels of the two major ventricular G proteins, Gia and Gsa in the heart after myocardial infarction(MI).Six week old rats were fed a Mg adequate or deficient diet for 6 weeks.At the end of week 3,MI was induced by coronary artery ligation.A sham operation was performed as control.After surgery,surviving animals were maintained on their assigned diets for another 3 weeks.Then,cardiac function was measured.Severe hypomagnesemia and increased plasma catecholamine level were observed in all animals fed the Mg deficient diet.A significant reduction of ruyocardial Mg concentration accompanied by elevated plasma and myocardial calcium concentrations was observed in MI animals with existing Mg deficiency vs.animals fed the Mg adequate diet.Cardiac function was impaired in MI rats and further reduced in MI rats with existing Mg deficiency. Gia level was not altered by either Mg deficiency or MI alone,but was dramatically elevated in animals with combined Mg deficiency and MI (9. 9±0.7 arbitrary unit.mg-1 protein) as compared to MI alone (5.8±0. 6,P<0.05 )and Mg deficiency alone(6.1± 0.8,P<0.05 ). Gsa level did not differ between groups.Bacal,GppNHp-and forskolin-but not fluoride-, stimulated adenylyl cyclase activity was signifcantly reduced in MI animals with existing Mg deficiency indicating increased functional activity of Gia.The findings suggest that dietary Mg deficiency increases the expression and functional ac tivity of Gia in the heart after MI, while levels and function of Gsa are not compromised during dietary Mg deficiency either with or without MI.

Magnesium-fortified phosphate fertilizers improve nutrient uptake and plant growth without reducing phosphorus availability

Magnesium(Mg)deficiency can significantly limit crop yield and quality.Separate application of straight Mg fertilizer is unattractive because of additional labor costs.Meanwhile,bulk blending Mg with other macronutrient fertilizers is also a suboptimal solution because bulk blended fertilizers often yield poor nutrient distributions.One rapid and economical alternative to alleviating Mg deficiency is to co-granulate macronutrient fertilizers with Mg.However,few commercial products have implemented this approach.One of the barriers hindering the production of Mg-fortified phosphorus(P)fertilizers is the assumption that precipitation of P with Mg will reduce P solubility.In this study,four Mg compounds,anhydrous magnesium sulfate(MgSO_(4)),magnesium oxide(MgO),anhydrous magnesium chloride(MgCl_(2)),and dolomite(CaMg(CO_(3))_(2)),were co-granulated with mono-ammonium phosphate(MAP),and their granule strength,Mg and P availabilities,and agronomic effectiveness were evaluated.Results showed that there were no significant differences in P solubility between Mg-fortified MAP and MAP treatments.X-ray diffraction(XRD)indicated that the Mg species after co-granulation were boussingaultite(Mg(NH_(4))_(2)(SO_(4))_(2)·6H_(2)O),schertelite(Mg(NH_(4))_(2)H_(2)(PO_(4))_(2)·4H_(2)O),magnesium hydrogen phosphate(Mg(H_(2)PO_(4))_(2)),and dolomite(CaMg(CO_(3))_(2)).A pot experiment using an acidic soil demonstrated an average 9.6-fold increase in shoot Mg uptake,3.0-fold increase in shoot P uptake,and 3.2-fold increase in soybean shoot dry matter in Mg-fortified MAP treatments,compared to those in MAP treatment.The current study provides a simple,effective,and low-cost approach for the addition of Mg to macronutrient fertilizers,to minimize Mg deficiency.