Astrocytes syncytium

FIGURE 5-14 Spatial buffering by astrocytes. This conceptual diagram indicates the pathways available for potassium ions to diffuse through the glial syncytium (light red) subsequent to their release from neuronal membranes (dark red) during neural activity. 

Astrocytes are responsible in maintaining extracellular ion concentration at a level compatible with neuronal function. Astrocytes form a syncytium through which it efficiently redistributes from perineuronal to perivascular space. Such redistribution of is mediated by inwardly rectifying ion channels. One such ion channel Kir 4.1 is expressed in astrocytes surrounding neuronal synapses as well as blood vessels in the brain (Nagelhus et al., 2004). 

In the brain, astrocytes form a syncytinm, or a network of integrated cells (Scemes, 2000). Snch a syncytium consists of astrocytes that have cytoplasmic continnity in adjacent cells... 

Castanospermine has been screened for efficacy against simian immunodeficiency virus (265), and has been shown to prevent syncytium formation in feline astrocyte cultures infected with the feline immimodeficiency virus by modifying the viral cell envelope (266). It suppressed syncytium formation and hemolytic activity in baby hamster kidney cells infected with Newcastle disease virus however, synthesis and cell surface expression of the hemagglutinin-neuraminidase glycoprotein in the viral envelope were not affected, which strengthens the hypothesis that poor transport of the parent alkaloid across membrane barriers may limit its therapeutic use (267). Both 239 and its 6-0-butanoyl ester had comparable relative toxicities and antiviral effects on Rauscher murine leukemia virus (268), but the ester was more potent than the parent alkaloid in inhibiting replication of Moloney murine leukemia virus (258). The ester was also active against herpes simplex viruses types 1 and 2 (269,270). In the latter case, conclusive evidence was provided for intracellular hydrolysis to 239. 

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