Intracellular Ca2+, Na+ and H+ transients evoked by kainate in the leech giant glial cells in situ.
The membrane responses to the glutamate receptor agonist kainate and the subsequent changes in intracellular Ca2+, H+ and Na+ concentration were measured in giant glial cells of the leech central nervous system using ion-selective microelectrodes and microfluorimetry of Fura-2. The membrane depolarization or membrane inward current of exposed neuropile glial cells in situ, evoked by 2-20 microM kainate, were reversibly blocked by 6-cyano-7-dinitroquinoxaline-2,3-dione (CNQX), (50-100 microM) and by Ni2+ (2 mM), but not by methoxyverapamil (D600, 500 microM), which blocked voltage-gated Ca2+ influx. Local iontophoretic application of kainate on to the somatic membrane of single neuropile glial cells in situ, resulted in CNQX-sensitive depolarization and rises in intraglial Ca2+ concentration similar to those observed with bath-application of the agonist, indicating the presence of non-N-methyl-D-aspartate-type (NMDA) glutamate receptors in the somatic membrane of these cells. In voltage-clamped glial cells bath-application of kainate (5-10 microM) evoked inward currents and an increase in the membrane conductance,. while the intracellular Ca2+ increased (up to 200 nM). This increase in Ca2+i was not affected by substitution of Na+ by Li+, indicating that it is not due to reversed Na+/Ca2 exchange following intracellular Na+ accumulation. The intracellular Na+ concentration increased (up to 40 mM), and the intracellular pH decreased (0.2-0.3 pH units) in voltage-clamped glial cells following bath application of kainate. All these changes of the concentration of intracellular cations were reversibly suppressed by CNQX and Ni2+. The results indicate that Ca2+, Na+ and H+ enter leech neuropile glial cells presumably through non-selective cation channels, activated by the non-NMDA glutamate receptor agonist kainate.
Munsch
T
T
Abteilung für Allgemeine Zoologie, FB Biologie, Universität Kaiserstautern, Germany.
Deitmer
J W
JW
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D016257:Fura-2; D005711:Gallopamil / Q000494:pharmacology; D017952:Ganglia, Invertebrate / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007608:Kainic Acid / Q000494:pharmacology*; D007700:Kinetics; D007865:Leeches; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009457:Neuroglia / Q000187:drug effects / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D017470:Receptors, Glutamate / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D017470:Receptors, Glutamate; D005711:Gallopamil; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D009532:Nickel; D012964:Sodium; D007608:Kainic Acid; D002118:Calcium; D016257:Fura-2