Differential role of two Ca(2+)-permeable non-NMDA glutamate channels in rat retinal ganglion cells: kainate-induced cytoplasmic and nuclear Ca2+ signals.
1. The permeability of non-N-methyl-D-aspartate (non-NMDA) glutamate channels to divalent cations and specifically the entry of Ca2+ and subsequent elevations in cytoplasmic and nuclear Ca2+ signals were investigated in cultured neonatal rat retinal ganglion cells using the whole cell patch-clamp technique and Ca2+ imaging with confocal microscopy. In addition, divalent-permeable non-NMDA receptor channels were studied in retinal slices using a Co2+ staining technique. 2. Using Ca2+ (2.5 mM) as the only permeable cation in the external solution, stimulation with 100 microM kainate produced nondesensitizing, nonselective cation currents with either low or high Ca2+ permeability. Both currents were reversibly blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Neurons with the low divalent-permeable currents (type 1) had reversal potentials of -41.5 +/- 4.4 mV (mean +/- SD), and neurons with the high divalent-permeable currents (type 2) had reversal potentials of -22.6 +/- 5.5 mV. The permeability ratio PCa/PCs was 3.3 for the type 1 currents and 8.5 for the type 2 currents, indicating a 2.5-fold greater permeability to Ca2+ for the type 2 non-NMDA glutamate channels. 3. Both types of non-NMDA glutamate channels showed relatively little selectivity between Ca2+ and Co2+. The type 1 neurons had a slightly higher permeability to Co2+ than to Ca2+, whereas the type 2 neurons were equally permeable to both divalent cations. The type 2 neurons had a much higher permeability for both divalent cations compared with the type 1 neurons. 4. Staining for Co2+ uptake through kainate-stimulated non-NMDA glutamate channels in retinal slices provided additional evidence for the presence of the two ganglion cell populations. Activation of the neurons by kainate in conditions isolating the non-NMDA glutamate channel caused differential uptake of Co2+. In contrast, depolarization in the presence of the non-NMDA antagonist CNQX failed to cause Co2+ influx. 5. Imaging experiments using confocal microscopy showed that kainate stimulation induced an increase in intracellular Ca2+ in both types of retinal ganglion cells, but only the type 2 neurons showed a substantial increase in cytoplasmic and nuclear Ca2+ signals. Kainate-induced Ca2+ signals in the type 2 neurons were almost nine times greater than those of the type 1 neurons. 6. When intracellular Ca2+ stores were depleted by brief treatment with thapsigargin, kainate-induced Ca2+ signals in the type 1 neurons were unchanged. However, in the type 2 neurons kainate no longer induced large Ca2+ signals in the cytoplasm and nucleus, despite normal influx of Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
Leinders-Zufall
T
T
Department of Neurology, Yale University School of Medicine, West Haven, Connecticut.
Rand
M N
MN
Waxman
S G
SG
Kocsis
J D
JD
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D002467:Cell Nucleus / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D003593:Cytoplasm / Q000187:drug effects* / Q000502:physiology; D007608:Kainic Acid / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018613:Microscopy, Confocal; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000187:drug effects* / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology
D015220:Calcium Channels; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D007608:Kainic Acid; D002118:Calcium