Fractional Ca2+ currents through somatic and dendritic glutamate receptor channels of rat hippocampal CA1 pyramidal neurones.
1. The Ca2+ permeability of non-NMDA and NMDA receptor channels was studied using a fluorometric flux measurement approach in somata and dendrites of CA1 pyramidal neurones in rat hippocampal slices. For this purpose, the Ca2+ fraction of the total cation current (named 'fractional Ca2+ current') was measured directly from the change in the Ca(2+)-sensitive fura-2 fluorescence at 380 nm excitation wavelength. 2. The fractional Ca2+ current through the somatic NMDA receptor channels was 10.69 +/- 2.13% (mean +/- S.D.) and that through dendritic receptor channels was 10.70 +/- 1.96%. The fractional Ca2+ current was not dependent on the extracellular Mg2+ concentration and its voltage dependence was in agreement with the Goldman-Hodgkin-Katz current equation. 3. AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate) or kainate applications produced small but significant Ca2+ entry. Fractional Ca2+ currents of 0.58 +/- 0.34% were measured for somatic AMPA applications, 0.68 +/- 0.20% for somatic kainate applications, 0.66 +/- 0.25% for dendritic AMPA applications and 0.61 +/- 0.16% for dendritic kainate applications. 4. The expression pattern of glutamate receptor subunits encoding messenger ribonucleic acids (mRNAs) was analysed with the single-cell reverse transcriptase-polymerase chain reaction (RT-PCR) approach applied to CA1 pyramidal neurones. The AMPA receptor subunits GluR-A, GluR-B and GluR-C, and the NMDA receptor subunits NR2A and NR2B were found to be abundantly expressed in all CA1 pyramidal neurones tested. 5. This study establishes the fractional Ca2+ current through somatic and dendritic NMDA and non-NMDA receptor channels in CA1 pyramidal neurones. The dendritic, presumably synaptic, NMDA receptor channels are highly Ca2+ permeable and have a fractional Ca2+ current closely resembling that of somatic extrasynaptic NMDA receptor channels. Both somatic and dendritic non-NMDA receptor channels are of the 'low Ca2+ permeable' type and have a fractional Ca2+ current that is about twenty times smaller than that of NMDA receptor channels.
Garaschuk
O
O
Physiologisches Institut, Universität des Saarlandes, Homburg, Germany.
Schneggenburger
R
R
Schirra
C
C
Tempia
F
F
Konnerth
A
A
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism*; D004594:Electrophysiology; D016257:Fura-2; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D017966:Pyramidal Cells / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism; D017470:Receptors, Glutamate / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism
D015220:Calcium Channels; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D008274:Magnesium; D016257:Fura-2