Extent of intercellular calcium wave propagation is related to gap junction permeability and level of connexin-43 expression in astrocytes in primarycultures from four brain regions

Astrocytes are coupled via gap junctions, predominantly formed by connexin- 43 proteins, into cellular networks. This coupling is important for the pro pagation of intercellular calcium waves and for the spatial buffering of K. Using the scrape-loading/dye transfer technique, we studied gap junction permeability in rat astrocytes cultured from four different brain regions. The cultures were shown to display regional heterogeneity with the followin g ranking of the gap junction coupling strengths: hippocampus = hypothalamu s > cerebral cortex = brain stem. Similar relative patterns were found in c onnexin-43 messenger RNA and protein levels using solution hybridization/RN ase protection assay and western blots, respectively. The percentages of th e propagation area of mechanically induced intercellular calcium waves for cortical, brain stem and hypothalamic astrocytes compared with hippocampal astrocytes were approximately 77, 42, and 52, respectively. Thus, the exten t of calcium wave propagation was due to more than just gap junctional perm eability as highly coupled hypothalamic astrocytes displayed relatively sma ll calcium wave propagation areas. Incubation with 5-hydroxytryptamine decr eased and incubation with glutamate increased the calcium wave propagation area in hippocampal (67% and 170% of the control, respectively) and in cort ical astrocytes (82% and 163% of the control, respectively). Contrary to hi ppo campal and cortical astrocytes, the calcium wave propagation in brain s tem astrocytes was increased by 5-hydroxytryptamine incubation (158% of con trol), while in hypothalamic astrocytes, no significant effects were seen. Similar effects from 5-hydroxytryptamine or glutamate treatments were obser ved on dye transfer, indicating an effect on the junctional coupling streng th. These results demonstrate a strong relationship between connexin-43 messeng er RNA levels, protein expression, and gap junction permeability among astr oglial cells. Furthermore, our results suggest heterogeneity among astrogli al cells from different brain regions in intercellular calcium signaling an d in its differential modulation by neurotransmitters, probably reflecting functional requirements in various brain regions. (C) 1999 IBRO. Published by Elsevier Science Ltd.