Characterization and Comparison of Calcium Oscillations Between Oligodendrocytes and Other Mammalian Cells

Mucolipidosis Type IV (MLIV) is an autosomal recessive lysosomal storage disorder of the nervous system characterized by severe motor impairment, delayed cognitive development, ophthalmological abnormalities, and a lack of myelin in the brain. It results from mutations that render the ion channel TRPML1 non-functional. TRPML1 is permeable to calcium, zinc, iron, and several other ions. Calcium is a vital ion in the propagation of electrical signals in the nervous system. Oligodendrocytes are the cell type in the central nervous system that produce myelin. As MLIV is a hypomyelinating disorder, studying calcium ion dynamics in oligodendrocytes may give significant insights into the molecular mechanisms underlying this pathological condition. We compared various calcium sensors (FuraRed, Fluo-4, GCamp5, RGECO-1, REXGECO1, and RCamp1h) in Hela cells on their sensitivity. Among these sensors, GCamp5 shows the greatest response to treatment with the drug thapsigargin, which increases cytosolic calcium by blocking the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), leading to release of calcium to the cytosol from the endoplasmic reticulum (ER). We then transfected various cell types with GCamp5 to compare the calcium dynamics of oligodendrocytes to more well studied cell types such as neurons. We also visualized the decrease of ER calcium concentrations in various cell types using the sensor ER-GCamp6-150. Finally, we discovered spontaneous calcium oscillations in mature rat oligodendrocytes that were exaggerated upon depolarization of the cell using 100 µM glutamate and 10 µM glycine. Given the important signaling roles of calcium, the calcium oscillations in oligodendrocytes might contribute to their vital function.