Calcium signaling in specialized glial cells

Abstract

This article reviews calcium signaling in three specialized types of glial cells: Müller cells of the retina, Bergmann glial cells of the cerebellum, and radial glial cells of the developing cortex. Müller cells generate spontaneous and neuronal activity-evoked increases in Ca(2+). Neuron to Müller cell signaling is mediated by neuronal release of ATP and activation of glial P2Y receptors. Müller cells, in turn, modulate neuronal excitability and mediate vasomotor responses. Bergmann glial cells also generate spontaneous and activity-evoked Ca(2+) increases. Neuron to Bergmann glia signaling is mediated by neuronal release of nitric oxide, noradrenaline, and glutamate. In Bergmann glia, Ca(2+) increases control the structural and functional interactions between these cells and Purkinje cell synapses. In the ventricular zone of the developing cortex, radial glial cells generate spontaneous Ca(2+) increases that propagate as Ca(2+) waves through clusters of neighboring glial cells. These Ca(2+) increases control cell proliferation and neurogenesis.

Fig. 1

Light-evoked Ca²⁺ signaling in Müller cells. (A) Calcium fluorescence measured simultaneously in eight Müller cells. The retina was exposed sequentially to a dim light, a bright flickering light, and a dim light (the light stimulus is shown at the bottom in A and B). Calcium transients are more likely to be generated during the flickering light stimulus. (B) Mean Ca²⁺ fluorescence averaged over 84 trials. The flickering light evokes both a transient and a sustained increase in Ca²⁺. From (Newman, 2005).

Fig. 2

Activity-evoked Ca²⁺ signaling in Bergmann glial cells. Calcium fluorescence measured in three cell processes of a Bergmann glial cell following electrical stimulation of parallel fibers. Stimulation evokes a Ca²⁺ increase in process 1 but not in processes 2 and 3 (traces on the left). Within process 1, microdomains 2 and 3, but not 1, 4 or 5, display stimulus-evoked Ca²⁺ increases (traces on the right). The right hand image shows the Bergmann glial cell from which the measurements were made. From (Grosche et al., 1999).

Fig. 3

Calcium signaling in radial glial cells. The nine pseudocolor Ca²⁺ fluorescence images show a Ca²⁺ wave propagating through a cluster of radial glial cells in the ventricular zone in embryonic cortical tissue. The spontaneous wave was likely initiated in the cell indicated by the arrow and propagated to adjacent cells by release of ATP. The images were acquired at 4 s intervals. From (Owens and Kriegstein, 1998).