Dietary and physiological studies to investigate to the relationship between calcium and magnesium signalling in the mammalian myocardium

• Published in: Molecular and cellular biochemistry 1997-11, Vol.176 (1/2), p.127-134
• Main Authors: Singh, J, Hustler, B.I, Waring, J.J, Howarth, F.C
• Format: Article
• Language: English
• Subjects: Animals; Calcium; Calcium - blood; Calcium - pharmacology; Calcium, Dietary - adverse effects; Cardiotonic Agents; Diet; diet-related diseases; Dose-Response Relationship, Drug; Female; Food; human nutrition; Magnesium; Magnesium - administration & dosage; Magnesium - blood; Magnesium - pharmacology; Magnesium Deficiency - physiopathology; Male; Mammals; Membrane Potentials - drug effects; Myocardial Contraction - drug effects; Myocardial Contraction - physiology; Myocardium - cytology; Myocardium - metabolism; Physiology; Plasma; Rabbits; Rats; Rats, Sprague-Dawley; Rodents; Signal Transduction - drug effects; Stimulation, Chemical
• ISSN: 0300-8177; 1573-4919
• DOI: 10.1023/A:1006839315221

This study employs both dietary and physiological studies to investigate the relationship between calcium (Ca2+) and magnesium (Mg2+) signalling in the mammalian myocardium. Rats maintained on a low Mg2+ diet (LMD; 39 mg Kg-1 Mg2+ in food) consumed less food and grew more slowly than control rats fed on a control Mg2+ diet (CMD; 500 mg Kg-1 Mg2+ in food). The Mg2+ contents of the heart and plasma were 85 +/- 3% and 34 +/- 6.5%, respectively relative to the control group. In contrast, Ca2+ contents in the heart and plasma were 177 +/- 5% and 95 +/- 3%. The levels of potassium (K+) was raised in the plasma (129 +/- 16%) and slightly decreased in the heart (88 +/- 6%) compared to CMD. Similarly, sodium (Na+) contents were slightly higher in the heart and lowered in the plasma of low Mg2+ diet rats compared to control Mg2+ diet rat. Perfusion of the isolated Langendorff's rat heart with a physiological salt solution containing low concentrations (0-0.6 mM) of extracellular magnesium [Mg2+]o resulted in a small transient increase in the amplitude of contraction compared to control [Mg2+]o (1.2 mM). In contrast, elevated [Mg2+]o (2-7.2 mM) caused a marked and progressive decrease in contractile force compared to control. In isolated ventricular myocytes the L-type Ca2+ current (ICa,L) was significantly (p < 0.001) attenuated in cells dialysed with 7.1 mM Mg2+ compared to cells dialysed with 2.9 microM Mg2+. The results indicate that hypomagnesemia is associated with decreased levels of Mg2+ and elevated levels of Ca2+ in the heart and moreover, internal Mg2+ is able to modulate the Ca2+ current through the L-type Ca2+ channel which in turn may be involved with the regulation of contractile force in the heart.