Glial Calcium: Homeostasis and Signaling Function

Abstract

Verkhratsky, Alexej, Richard K. Orkand, and Helmut Kettenmann. Glial Calcium: Homeostasis and Signaling Function. Physiol. Rev. 78: 99–141, 1998. — Glial cells respond to various electrical, mechanical, and chemical stimuli, including neurotransmitters, neuromodulators, and hormones, with an increase in intracellular Ca 2+concentration ([Ca 2+]i). The increases exhibit a variety of temporal and spatial patterns. These [Ca 2+]i responses result from the coordinated activity of a number of molecular cascades responsible for Ca 2+movement into or out of the cytoplasm either by way of the extracellular space or intracellular stores. Transplasmalemmal Ca 2+movements may be controlled by several types of voltage- and ligand-gated Ca 2+-permeable channels as well as Ca 2+pumps and a Na+/Ca 2+exchanger. In addition, glial cells express various metabotropic receptors coupled to intracellular Ca 2+stores through the intracellular messenger inositol 1,4,5-trisphosphate. The interplay of different molecular cascades enables the development of agonist-specific patterns of Ca 2+responses. Such agonist specificity may provide a means for intracellular and intercellular information coding. Calcium signals can traverse gap junctions between glial cells without decrement. These waves can serve as a substrate for integration of glial activity. By controlling gap junction conductance, Ca 2+waves may define the limits of functional glial networks. Neuronal activity can trigger [Ca 2+]i signals in apposed glial cells, and moreover, there is some evidence that glial [Ca 2+]i waves can affect neurons. Glial Ca 2+signaling can be regarded as a form of glial excitability.