Severe dietary magnesium deficiency does not alter levels and function of myocardial G(s)α and G(i)α

Magnesium ions (Mg²⁺) play a crucial role in the activation and synthesis of guanine nucleotide-binding proteins (G proteins). However, there is no information about the influence of in vivo magnesium deficiency on the function and levels of G proteins. This study was done to investigate whether dietary magnesium deficiency alters function and levels of the two major myocardial G proteins, G(i)α and G(s)α. Severe hypomagnesemia and a significant reduction of myocardial magnesium occurred in rats fed a magnesium-deficient diet for 6 wk vs. rats fed a normal-magnesium diet (control). The magnesium-deficient rats developed focal myocardial lesions but their cardiac function was not impaired. Myocardial immunodetectable G(s)α and G(i)α levels of magnesium-deficient rats did not differ from control (G(s)α: 2.39 ± 0.52 vs. 2.76 ± 0.72 arbitrary units/μg protein, P > 0.05; G(i)α: 1.60 ± 0.52 vs. 1.89 ± 0.30 arbitrary units/μg protein, P > 0.05). Similarly, the function of G(s)α and G(i)α estimated by basal and ligand-stimulated adenylyl cyclase activity was not significantly different between the two groups of animals. The results show that dietary-derived magnesium deficiency sufficient to produce severe hypomagnesemia does not produce any significant change in levels or function of myocardial G proteins.