Alteration in cardiomyocyte mechanics by suboptimal levels of extracellular magnesium

The beneficial effects of magnesium supplementation in pathological situati ons is well known, but the myocardial response to a nominal decrease in the level of magnesium has received relatively little attention. Hypomagnesemi a can occur as chronic or acute manifestation of physiological changes, pat hological conditions, or pharmacological interventions. Experimental intere st was focused on the mechanical changes in adult rat heart myocytes follow ing variation in extracellular Mg2+. Isolated cells were exposed to differe nt levels of extracellular Mg2+ and the amplitude and rate of contraction w ere measured as a function of change in cell length using a video-based edg e-detection system. Investigations have revealed that variation in the leve l of Mg2+ within physiological limits leads to mechanical changes. A decrea se in the level of extracellular Mg2+ was accompanied by a significant incr ease in contractile amplitude and decrease in the velocities of contraction and relaxation. The contractile amplitude measured as percentage shortenin g were 3.08 +/- 0.19%, 4.62 +/- 0.19% and 6.9 +/- 0.40%, respectively, on e xposure to 1.8, 0.8, and 0.48 mM Mg, and the corresponding velocities of co ntraction and relaxation normalized to amplitude were 0.54 +/- 0.02, 0.40 /- 0.03, 0.31 +/- 0.03 and 0.47 +/- 0.02, 0.35 +/- 0.02, 0.24 +/- 0.02. The variations in contractile parameters associated with the change in the lev el of Mg were statistically significant (p < 0.01). Variation in the contra ctile properties associated with change in extracellular Mg2+ may be effect ed by alteration in Ca2+ transients.