title: A patch clamp study of excitatory amino acid effects on cortical astrocyte subtypes in culture.
abstract: Electrophysiological effects of the excitatory amino acids (EAAs) glutamate (Glu) and kainate (KA) on membrane properties of confluent (> 7-9 day) astrocyte cultures were examined. The whole-cell patch clamp technique was employed to measure membrane currents. Cells were subdivided antigenically, morphologically and electrophysiologically into type-1-like and type-2 astrocytes. Lucifer yellow injection showed that type-1-like, but not type-2, astrocytes were electrically coupled in type-2 astrocytes, EAAs induced a cationic current by activating an ionotropic Glu receptor. The underlying receptor mechanism was KA-preferring and was blocked by the broad-spectrum EAA receptor channel antagonist kynurenate (Kyn). The current was dose-dependent and gave a Hill coefficient close to 2 for KA. In type-1-like astrocytes, EAA effects were agonist-dependent. Glu action involved an inward current mainly carried by an electrogenic Glu uptake system. This current was suppressed by the Glu uptake blocker DL-aspartate beta hydroxamate (ABH), but was not sensitive to Kyn. On the other hand, KA activated Kyn-sensitive receptors and was still able to induce this current in the presence of ABH. In type-1-like astrocytes, application of KA on average produced no conductance change. However, application of Ringer containing 5 mM Ba2+ caused a significant increase in input resistance and KA applied in the presence of Ba2+ consistently increased input conductance. In both subtypes of astrocyte, the KA-induced current was predominantly Na(+)-dependent, although in type-2 cells a small, Na(+)-independent current was also seen. These results support recent findings that type-1-like and type-2 astrocytes possess KA-preferring ionotropic receptors and type-1-like astrocytes also possess an electrogenic Glu uptake system.
authors.affiliation: Department of Biochemistry, Imperial College of Science, Technology and Medicine, London, United Kingdom.
authors.forename: G J
authors.initials: GJ
authors.lastname: Stephens
authors.forename: M B
authors.initials: MB
authors.lastname: Djamgoz
authors.forename: G P
authors.initials: GP
authors.lastname: Wilkin
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001216:Asparagine / Q000031:analogs & derivatives / Q000494:pharmacology; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D007608:Kainic Acid / Q000494:pharmacology*; D008564:Membrane Potentials; D051381:Rats; D017459:Receptors, Amino Acid / Q000378:metabolism
chemical_list: D005971:Glutamates; D017459:Receptors, Amino Acid; C024848:beta-aspartylhydroxamic acid; D018698:Glutamic Acid; D001216:Asparagine; D007608:Kainic Acid