Effects of Magnesium on Cardiac Excitation-Contraction Coupling

Objective: Magnesium regulates a large number of cellular processes. Small changes in intracellular free Mg²⁺ ([Mg²⁺]_i) may have important effects on cardiac excitability and contractility. We investigated the effects of [Mg²⁺]_i on cardiac excitation-contraction coupling.

Methods: We used our ionic-metabolic model that incorporates equations for Ca²⁺ and Mg²⁺ buffering and transport by ATP and ADP and equations for MgATP regulation of ion transporters (Na⁺-K⁺ pump, sarcolemmal and sarcoplasmic Ca²⁺ pumps).

Results: Model results indicate that variations in cytosolic Mg²⁺ level might sensitively affect diastolic and systolic Ca²⁺, sarcoplasmic Ca²⁺ content, Ca²⁺ influx through L-type channels, efficiency of the Na⁺/Ca²⁺ exchanger and action potential shape. The analysis suggests that the most important reason for the observed effects is a modified normal function of sarcoplasmic Ca²⁺-ATPase pump by altered diastolic MgATP levels.

Conclusion: The model is able to reproduce qualitatively a sequence of events that correspond well with experimental observations during cardiac excitation-contraction coupling in mammalian ventricular myocytes.