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.
School of Medicine, Department of Cell Biology, Yale University, New Haven, CT 06510.
S H
SH
Lee
W T
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Kim
A H
AH
Cornell-Bell
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Sontheimer
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