Mok. Enkvist et Kd. Mccarthy, ASTROGLIAL GAP JUNCTION COMMUNICATION IS INCREASED BY TREATMENT WITH EITHER GLUTAMATE OR HIGH K+ CONCENTRATION, Journal of neurochemistry, 62(2), 1994, pp. 489-495
Astroglia are extensively coupled by gap junctions and form a function
al syncytium. Astroglial gap junctions are thought to be involved in t
he spatial buffering of K+ in vivo and in the Ca2+ waves seen on gluta
mate receptor activation. The conductivity of gap junctions is regulat
ed by several second messengers, with up-regulation by cyclic AMP and
down-regulation through activation of protein kinase C, decreases in i
ntracellular pH, or increases in the free cytosolic Ca2+ concentration
. The results presented here indicate that dye coupling of astroglia i
s significantly up-regulated by membrane depolarization, both by incre
ases in the extracellular K+ concentration and directly by ionophores.
Furthermore, glutamate, kainate, and quisqualate, which depolarize as
troglial cells through activation of ionotropic receptors, also increa
se dye coupling in astroglia. The effect of kainate and quisqualate wa
s reversed by 6-cyano-7-nitroquinoxaline-2,3-dione, an inhibitor of th
e ionotropic glutamate receptor. A dose-dependent decrease in dye coup
ling was seen when the cells were injected with increasing concentrati
ons of Ca2+. However, if the cells were simultaneously depolarized, th
e inhibitory effect of Ca2+ on gap junctional conductance was reversed
. Significant increases over basal coupling was attained when the cell
s were injected with Ca2+ if they were treated with kainate or Kf. The
se data suggest that ligands that depolarize astroglia enhance gap jun
ction communication between astroglia and that this enhancement may be
important in maintaining communication between astroglia in the face
of elevated Ca2+ levels.