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Cardiovascular Research 1995 30(6):923-929; doi:10.1016/S0008-6363(95)00143-3
© 1995 by European Society of Cardiology
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Copyright © 1995, European Society of Cardiology

Dietary magnesium deficiency increases Gi{alpha} levels in the rat heart after myocardial infarction

Bing Shi*, James E. Heavnerb, c, L.Mallory Boylana, Martin J. Wangd and Julian E. Spallholza

aFood and Nutrition, Texas Tech University, Lubbock, TX 79430, USA
bDepartment of Anesthesiology, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
cDepartment of Physiology, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
dBioMedical Consulting, 755 Plumtree Lane, Claymont, DE 19703-16H, USA

* Corresponding author (address b). Tel. (+1-806) 743-2916; Fax (+1-806) 743-2984.

Objective: 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 altered in 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, Gi{alpha} and Gs{alpha} in the heart after myocardial infarction (MI). Methods: Six week old rats were fed an 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, plasma and tissue were collected. Results: Severe hypomagnesemia and increased plasma catecholamine level were observed in all animals fed the Mg deficient diet. A significant reduction of myocardial 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. Gi{alpha} 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). Gs{alpha} level did not differ between groups. GppNHp-, but not fluoride-stimulated adenylyl cyclase activity was slightly reduced in MI animals with existing Mg deficiency. Conclusion: The findings suggest that dietary Mg deficiency increases the expression of Gi{alpha} in the heart after MI, while levels and function of Gs{alpha} are not compromised during dietary Mg deficiency either with or without MI.

KEYWORDS G-proteins; Magnesium; Myocardial infarction; Myocardial function; Adenylyl cyclase; Catecholamines; Rat; heart


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