Calcium signaling in terminal Schwann cells associated with lanceolate sensory endings in rat vibrissae

Transient elevations of the intracellular Ca2+ concentration ([Ca2+]i) in glia mediate various cell activities to regulate neuronal functions. The present study focuses on spatiotemporal dynamics of Ca2+ signaling in terminal Schwann cells, glial elements of the lanceolate sensory endings innervating the rat vibrissa. Arrays of lanceolate endings were enzymatically isolated from the vibrissal follicle, and subjected to [Ca2+]i image recording by time-lapse confocal microscopy. Each terminal Schwann cell displayed a round cell body, and extended long cytoplasmic stalks, which branched into two to five lamellae resting on different axon endings. Each axon ending, on the other hand, was covered on both flattened sides of the lancet by two Schwann lamellae of different cell origin. Thus the peripheral glia constituted an extensive network connecting the sensory endings. Image analyses of [Ca2+]i characterized the Schwann lamellae as functional compartments that can independently generate Ca2+ signals: these cell portions primarily responded to local mechanical stimuli with a [Ca2+]i spike, and individually initiated [Ca2+]i oscillations during bath application of the sensory modulator adenosine 5'-triphosphate (ATP). The stimulus-induced signals sometimes propagated along the glial network to activate neighboring lamellae after a delay of 2-4 sec. These findings suggest that the terminal Schwann cells contribute both to individual regulation and total coordination of the arrayed sensory endings.