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Gap junctions equalize intracellular Na + concentration in astrocytes
Author(s) -
Rose Christine R.,
Ransom Bruce R.
Publication year - 1997
Publication title -
glia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.954
H-Index - 164
eISSN - 1098-1136
pISSN - 0894-1491
DOI - 10.1002/(sici)1098-1136(199708)20:4<299::aid-glia3>3.0.co;2-1
Subject(s) - gap junction , extracellular , intracellular , biophysics , heptanol , sodium , hippocampal formation , biology , neuroglia , astrocyte , membrane potential , biochemistry , chemistry , endocrinology , central nervous system , organic chemistry
Gap junctions between glial cells allow intercellular exchange of ions and small molecules. We have investigated the influence of gap junction coupling on regulation of intracellular Na + concentration ([Na + ] i ) in cultured rat hippocampal astrocytes, using fluorescence ratio imaging with the Na + indicator dye SBFI (sodium‐binding benzofuran isophthalate). The [Na + ] i in neighboring astrocytes was very similar (12.0 ± 3.3 mM) and did not fluctuate under resting conditions. During uncoupling of gap junctions with octanol (0.5 mM), baseline [Na + ] i was unaltered in 24%, increased in 54%, and decreased in 22% of cells. Qualitatively similar results were obtained with two other uncoupling agents, heptanol and α‐glycyrrhetinic acid (AGA). Octanol did not alter the recovery from intracellular Na + load induced by removal of extracellular K + , indicating that octanol's effects on baseline [Na + ] i were not due to inhibition of Na + , K + ‐ATPase activity. Under control conditions, increasing [K + ] o from 3 to 8 mM caused similar decreases in [Na + ] i in groups of astrocytes, presumably by stimulating Na + , K + ‐ATPase. During octanol application, [K + ] o ‐induced [Na + ] i decreases were amplified in cells with increased baseline [Na + ] i , and reduced in cells with decreased baseline [Na + ] i . This suggests that baseline [Na + ] i in astrocytes “sets” the responsiveness of Na + , K + ‐ATPase to increases in [K + ] o . Our results indicate that individual hippocampal astrocytes in culture rapidly develop different levels of baseline [Na + ] i when they are isolated from one another by uncoupling agents. In astrocytes, therefore, an apparent function of coupling is the intercellular exchange of Na + ions to equalize baseline [Na + ] i , which serves to coordinate physiological responses that depend on the intracellular concentration of this ion. GLIA 20:299–307, 1997. © 1997 Wiley‐Liss, Inc.