AUTOCELLULAR COUPLING BY GAP-JUNCTIONS IN CULTURED ASTROCYTES - A NEWVIEW ON CELLULAR AUTOREGULATION DURING PROCESS FORMATION

Neocortical astrocytes make two types of gap junctions, intercellular ones create a functional syncytium, while reflexive gap junctions medi ate autocellular coupling and serve unknown functions (Rohlmann and Wo lff, 1996). Here, the question is addressed whether solitary astrocyte s in vitro express connexin43 (Cx43) and establish gap junctions in th e absence of intercellular contacts. In all media conditions tested, i mmunocytochemistry visualized Cx43-expression and gap junctions irresp ective of the presence or absence of intercellular contacts. Reflexive gap junctions were associated with mechanical junctions (adherent spo ts and fascia adherens) connecting surface membranes and cytoskelal co mponents, respectively. Both were characteristically located along inc ompletely separated borders between developing processes and/or branch es. In addition, Cx43-immunoreactivity was found on some non-junctiona l membranes: i) intracellular vesicle clusters sited to forming proces ses and at the basis of filopodia; ii) the surface membrane of filopod ial subpopulations usually appearing in bunches. Results suggest chang es in the resumptive role of Cx43 in cultivated astrocytes: 1) Cx43 is not confined to intercellular gap junctions, it may even selectively compose reflexive ones; 2) from intracellular stores (vesicle aggregat es), Cx43 may be incorporated into the surface membrane of filopodia; 3) by contacting other parts of the same cell surface (or neighboring cells), filopodia and membrane patches carrying Cx43-half channels may be essential in initial steps of gap junction formation; 4) the distr ibution of reflexive gap junctions is compatible with the hypothesis t hat autocellular coupling serves reorganization of cytoskeleton during the formation of cell processes and branches; 5) in general, gap junc tions may be important for coordinating the cytoskeleton across interc ellular contacts and within cells with complex shape. GLIA 24.121-140, 1998. (C) 1998 Wiley-Liss, Inc.