ASTROCYTES EXHIBIT REGIONAL SPECIFICITY IN GAP-JUNCTION COUPLING

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.