Astrocytes exhibit regional specificity in gap-junction coupling.
Astrocytes are coupled to each other via gap-junctions both in vivo and in vitro. Gap-junction coupling is essential to a number of astrocyte functions including the spatial buffering of extracellular K+ and the propagation of Ca2+ waves. Using fluorescence recovery after photo-bleach, we quantitatively assayed and compared the coupling of astrocytes 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 coupling strength. Gap-junction coupling differed markedly between CNS regions. Coupling was weakest in astrocytes derived from spinal cord (43% recovery, tau approximately 400 s) and strongest in astrocytes from optic nerve (91% recovery, tau approximately 226 s) and cerebellum (95% recovery, tau approximately 100 s). As indicated by the degree of recovery, coupling strength among CNS regions could be ranked as follows: spinal cord < cortex < hypothalamus < hippocampus = optic nerve = cerebellum. Gap-junction coupling also differed between CNS regions with respect to its sensitivity to inhibition by the uncoupling agent octanol. Kd values for 50% inhibition by octanol ranged from 188 microM in spinal cord astrocytes to 654 microM in hippocampal astrocytes. Sensitivity of gap-junctions to octanol could be ranked as follows: spinal cord = cortex = hypothalamus > cerebellum > optic nerve > hippocampus. The observed differences in coupling indicate differences in the number of gap-junction connections in astrocytes cultured from the six CNS regions. These differences may reflect the adaptation of astrocytes to varying functional requirements in different CNS regions.
Lee
S H
SH
School of Medicine, Department of Cell Biology, Yale University, New Haven, CT 06510.
Kim
W T
WT
Cornell-Bell
A H
AH
Sontheimer
H
H
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002490:Central Nervous System / Q000166:cytology*; D005452:Fluoresceins; D005453:Fluorescence; D005456:Fluorescent Dyes; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D018613:Microscopy, Confocal; D000442:Octanols / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D005452:Fluoresceins; D005456:Fluorescent Dyes; D000442:Octanols; C024098:6-carboxyfluorescein