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 (0-9.6 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 (I(Ca,L)) was significantly (p < 0.001) attenuated in cells dialysed with 7.1 mM Mg2+ compared to cells dialysed with 2.9 μM 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.
- Dietary and L-type calcium current
ASJC Scopus subject areas
- Molecular Biology
- Clinical Biochemistry
- Cell Biology