INTERCELLULAR CALCIUM SIGNALING AND GAP JUNCTIONAL COMMUNICATION IN ASTROCYTES

Two main characteristics of astrocytes are their elaborated intracellu lar calcium signaling and their high degree of intercellular communica tion mediated by gap junctional channels. In these cells a number of s tudies have contributed to demonstrate that the combination of these t wo properties provides a basis for a long-range signaling system withi n the brain. Intercellular calcium signaling, also termed calcium wave s, allows astrocytes to communicate with each other and to interact wi th adjacent neurons. Most of the intra- and inter-cellular events invo lved in the initiation and propagation phases of this process has now been identified. This sequence of events includes the permeability of gap junction channels, which at the time-scale for calcium waves propa gation, are likely permeated rather than closed by Ca2+ and/or related signaling molecules like IP3. In addition, in some studies an externa l component have been reported to participate to the propagation proce ss. Finally, the control of the spread of intercellular calcium signal ing has been demonstrated to occur at several levels including phospho lipase C, IP3 receptors, intracellular Ca2+ stores, and cytoplasmic Ca 2+ buffering. Accordingly, normal and pathological situations that aff ect one or several of these steps can be predicted to influence on ast rocytic calcium waves. GLIA 24:50-64, 1998. (C) 1998 Wiiey-Liss, Inc.