Mechanisms of transmitter release from astrocytes

Abstract

Astrocytes and other glial cells can release a variety of neuroligands into the extracellular space using many different mechanisms. In this chapter we chiefly discuss the different chemical transmitters that astrocytes have been shown to release and examine the mechanisms by which these cells release the transmitters. In limited cases we expand our discussion on this subject to other astrocyte-related cells, such as Müller cells, pituicytes, as well as cell lines, including tumorigenic astrocytomas and gliomas. We focus on transmitters released from astrocytes, apart from eicosatetraenoids (briefly discussed in Chap. 18), growth factors and hormones (see Chap. 13). Transmitters can be released by astrocytes through several different mechanisms: (1) through channels like anion channel opening induced by cell swelling (Pasantes Morales and Schousboe, 1988), release through functional unpaired connexons, hemichannels, on the cell surface (Cotrina et al., 1998) and ionotropic purinergic receptors (Duan et al., 2003); (2) through transporters such as reversal of uptake by plasma membrane excitatory amino acid transporters (Szatkowski et al., 1990), exchange via the cystine-glutamate antiporter (Warr et al., 1999) or organic anion transporters (Rosenberg et al., 1994); and (3) through Ca 2+-dependent exocytosis (Parpura et al., 1994).