Fura-2 signals evoked by kainate in leech glial cells in the presence of different divalent cations.
The glutamate-agonist kainate evokes Ca2+ transients in both neurones and glial cells. Owing to the membrane depolarization elicited by kainate, a Ca2+ influx could occur through voltage-gated Ca2+ channels or through the kainate-gated cation channels directly. We have measured ratio signals of the calcium indicator dye fura-2, injected into giant glial cells of the leech Hirudo medicinalis, as response to kainate (5-20 microM) in the presence of different divalent cations. The responses to kainate increased during the first 2-4 kainate applications, both in unclamped and in voltage-clamped cells. The fura-2 fluorescence ratio (F350/F380) still increased when Ca2+ was replaced by Ba2+ but was suppressed in Ca(2+)-free saline and in the presence of Ni2+ (2 mM). Co2+ and Mn2+ (2 mM) also reduced the kainate-induced fura-2 fluorescence signals, due to entry of these divalent cations into the cells and subsequent quenching the fluorescence of the intracellular dye. It is concluded that Ni2+ blocks the kainate-induced membrane depolarization and Ca2+ transient but apparently does not enter the cells, while Ba2+, Co2+, and Mn2+ appear to permeate the membrane, presumably through the kainate-gated channels.
Munsch
T
T
Abteilung für Allgemeine Zoologie, Universität Kaiserslautern, Germany.
Nett
W
W
Deitmer
J W
JW
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002413:Cations, Divalent / Q000494:pharmacology*; D016257:Fura-2; D017952:Ganglia, Invertebrate / Q000187:drug effects / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D007608:Kainic Acid / Q000494:pharmacology*; D007865:Leeches / Q000502:physiology*; D009457:Neuroglia / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D013050:Spectrometry, Fluorescence
D015220:Calcium Channels; D002413:Cations, Divalent; D007608:Kainic Acid; D002118:Calcium; D016257:Fura-2