title: Dietary and physiological studies to investigate the relationship between calcium and magnesium signalling in the mammalian myocardium.
abstract: 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.
authors.affiliation: Department of Applied Biology, University of Central Lancashire, Preston, England, UK.
authors.forename: J
authors.initials: J
authors.lastname: Singh
authors.forename: B I
authors.initials: BI
authors.lastname: Hustler
authors.forename: J J
authors.initials: JJ
authors.lastname: Waring
authors.forename: F C
authors.initials: FC
authors.lastname: Howarth
mesh_terms: D000818:Animals; D002118:Calcium / Q000097:blood / Q000494:pharmacology*; D002136:Calcium, Dietary / Q000009:adverse effects; D002316:Cardiotonic Agents; D004305:Dose-Response Relationship, Drug; D005260:Female; D008274:Magnesium / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D008275:Magnesium Deficiency / Q000503:physiopathology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013268:Stimulation, Chemical
chemical_list: D002136:Calcium, Dietary; D002316:Cardiotonic Agents; D008274:Magnesium; D002118:Calcium