Astrocytes are coupled to each other via gap-junctions both in vivo an
d in vitro. Gap-junction coupling is essential to a number of astrocyt
e functions including the spatial buffering of extracellular K+ and th
e propagation of Ca2+ waves. Using fluorescence recovery after photo-b
leach, we quantitatively assayed and compared the coupling of astrocyt
es cultured from six different central nervous system (CNS) regions in
the rat: spinal cord, cortex, hypothalamus, hippocampus, optic nerve,
and cerebellum. The degree of fluorescence recovery (% recovery) and
time constant of recovery (tau) served as quantitative indicators of c
oupling strength. Gap-junction coupling differed markedly between CNS
regions. Coupling was weakest in astrocytes derived from spinal cord (
43% recovery, tau similar to 400 s) and strongest in astrocytes from o
ptic nerve (91% recovery, tau similar to 226 s) and cerebellum (95% re
covery, tau similar to 100 s). As indicated by the degree of recovery,
coupling strength among CNS regions could be ranked as follows: spina
l cord < cortex < hypothalamus < hippocampus = optic nerve = cerebellu
m. Gap-junction coupling also differed between CNS regions with respec
t to its sensitivity to inhibition by the uncoupling agent octanol. Kd
values for 50% inhibition by octanol ranged from 188 mu M in spinal c
ord astrocytes to 654 mu M in hippocampal astrocytes. Sensitivity of g
ap-junctions to octanol could be ranked as follows: spinal cord = cort
ex = hypothalamus > cerebellum > optic nerve > hippocampus. The observ
ed differences in coupling indicate differences in the number of gap-j
unction connections in astrocytes cultured from the six CNS regions. T
hese differences may reflect the adaptation of astrocytes to varying f
unctional requirements in different CNS regions. (C) 1994 Wiley-Liss,
Inc.