Subcellular heterogeneity of voltage-gated Ca2+ channels in cells of the oligodendrocyte lineage.

We studied the distribution of voltage-gated Ca2+ channels in cells of the oligodendrocyte lineage from retinal and cortical cultures. Influx of Ca2+ via voltage-gated channels was activated by membrane depolarization with elevated extracellular K+ concentration ([K+]e) and local, subcellular increases in cytosolic free Ca2+ concentration ([Ca2+]in) could be monitored with a fluometric system connected to a laser scanning confocal microscope. In glial precursor cells from both retina and cortex, small depolarizations (with 10 or 20 mM K+) activated Ca2+ transients in processes indicating the presence of low-voltage-activated Ca2+ channels. Larger depolarizations (with 50 mM K+) additionally activated high-voltage-activated Ca2+ channels in the soma. An uneven distribution of Ca2+ channels was also observed in the mature oligodendrocytes; Ca2+ transients in processes were considerably larger. Recovery of Ca2+ levels after the voltage-induced influx was achieved by the activity of the plasmalemmal Ca2+ pump, while mitochondria played a minor role to restore Ca2+ levels after an influx through voltage-operated channels. During the development of white matter tracts, cells of the oligodendrocyte lineage contact axons to form myelin. Neuronal activity is accompanied by increases in [K+]e; this may lead to Ca2+ changes in the processes and the Ca2+ increases might be a signal for the glial precursor cell to start myelin formation.