Do Magnesium Ions Have Similar Effects as Calcium Ions on Resting Membrane Potential?

TL;DR

This study investigates how magnesium ions affect resting membrane potential in Drosophila larval muscles compared to calcium ions.

Contribution

The study reveals that magnesium ions have minimal direct effects on membrane potential compared to calcium ions.

Findings

Mg2+ changes up to 20 mM caused only 1–2 mV shifts in membrane potential.

Ca2+ changes of 3–5 mM caused larger shifts (5–10 mV) in membrane potential.

High Mg2+ levels may dampen the effects of Ca2+ on membrane potential.

Abstract

Maintaining a membrane electrical potential of biological cells is a dynamic process, as some cells have a continually changing potential, like pacemaker cells, while other cells may function with large or small changes in the membrane potential. Additionally, some cells may change their electrical potential when stimulated or inhibited by electrical signals, chemical compounds, or both—either simultaneously or episodically. The persistent leak of K+ through two-pore-domain potassium channels (K2P) and of Na+ through Na+ leak channels (NALCNs) and the action of pumps and exchangers are primarily responsible for maintaining a resting potential. Ca2+ ions are known to block the NALCNs and result in a more hyperpolarized membrane potential, with a reduction in Ca2+ resulting in a depolarized state. Using the larval muscles of Drosophila, the membrane potentials were monitored as Ca2+ and Mg2+ concentrations were altered. Changes as large as 20 mM of Mg2+ had only small effects (1 to 2 mV) on the membrane potential compared to 3–5 mM changes in Ca2+ having larger effects (5–10 mV). Although, it appears raised [Mg2+] may dampen the changes induced by Ca2+. Simulations of the G-H-K equation estimate the changes in permeability of Na+ (pNa). These experiments are significant, as the clinical severity of hypocalcemia and hypercalcemia may also depend on Mg2+ levels.

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