Kainate activates Ca(2+)-permeable glutamate receptors and blocks voltage-gated K+ currents in glial cells of mouse hippocampal slices.
Glial cells in the CA1 stratum radiatum of the hippocampus of 9- to 12-day-old mice show intrinsic responses to glutamate due to the activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainate receptors. In the present study we have focused on a subpopulation of the hippocampal glial cells, the "complex" cells, characterized by voltage-gated Na+ and K+ channels. Activation of glutamate receptors in these cells led to two types of responses, the activation of a cationic conductance, and a longer-lasting blockade of voltage-gated K+ channels. In particular, the transient (inactivating) component of the outwardly rectifying K+ current was diminished by kainate. Concomitantly, as described in Bergmann glial cells, kainate also elevated cytosolic Ca2+. This increase was due to an influx via the glutamate receptor itself. In contrast to Bergmann glial cells, the cytosolic Ca2+ increase was not a link to the K+ channel blockade, since the blockade occurred in the absence of the Ca2+ signal and, vice versa, an increase in cytosolic Ca2+ induced by ionomycin did not block the transient K+ current. We conclude that glutamate receptor activation leads to complex and variable changes in different types of glial cells; the functional importance of these changes is as yet unresolved.
Jabs
R
R
Institute of Physiology, Friedrich-Schiller University Jena, Germany.
Kirchhoff
F
F
Kettenmann
H
H
Steinhäuser
C
C
D000818:Animals; D001711:Biotransformation / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004566:Electrodes; D004594:Electrophysiology; D005434:Flow Cytometry; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects*; D007608:Kainic Acid / Q000494:pharmacology*; D051379:Mice; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D018091:Receptors, AMPA / Q000187:drug effects; D017470:Receptors, Glutamate / Q000187:drug effects*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism
D015220:Calcium Channels; D015221:Potassium Channels; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D015222:Sodium Channels; D007608:Kainic Acid; D002118:Calcium