Visualization of long-term Mg(2+) dynamics in apoptotic cells using a novel targetable fluorescent probe

Mg(2+) plays important roles in many physiological processes. However, the underlying molecular mechanisms, especially in the apoptotic pathway, remain unclear due to the diffusion of Mg(2+) probes, which hinders long-term imaging in specific organelles. We developed an immobilized Mg(2+) probe, MGH, which is covalently conjugated with the HaloTag protein in various organelles. HaloTag-coupled MGH enabled long-term imaging of intracellular local Mg(2+) dynamics for 24 h. To exploit this remarkable property, MGH was applied to the investigation of intracellular Mg(2+) dynamics during apoptosis. Time-lapse imaging revealed an increase in the Mg(2+) concentration after apoptotic cell shrinkage. Combined imaging analyses of intracellular Mg(2+) and ATP concentrations strongly suggested that this Mg(2+) concentration increase was caused by the dissociation of Mg(2+) from ATP, along with a decrease in the intracellular ATP concentration. Thus, this protein-coupled Mg(2+) probe could be a new chemical tool to elucidate intracellular Mg(2+) dynamics with high spatiotemporal resolution.