Fractional calcium current through neuronal AMPA-receptor channels with a low calcium permeability.
The Ca(2+)-permeation properties of AMPA-receptor (AMPA-R) channels in Purkinje neurons in rat cerebellar slices were studied using a combination of whole-cell patch-clamp recordings, Fura-2 fluorometry, and single-cell reverse-transcription (RT)-PCR. Several lines of evidence indicate that Purkinje neurons, at both early and late stages of postnatal development, express exclusively AMPA-R channels with a low Ca2+ permeability. First, no Ca2+ signal was detected during application of either AMPA or kainate to Purkinje neurons loaded with the Ca2+ indicator Fura-2 AM. In contrast, kainate application induced large Ca2+ transients in Bergmann glia cells. Second, in ion substitution experiments, when Ca2+ is the only extracellular permeant cation, the reversal potential corresponds to that expected for AMPA-R channels with a low permeability for Ca2+. Third, using a fluorometric flux-measurement approach (Schneggenburger et al., 1993a), we found that the Ca2+ fraction of the total cation current through AMPA-R channels is approximately 0.6%. This value is approximately sixfold lower than that found for recombinant AMPA-R lacking the AMPA-R subunit GluR2. Furthermore, single-cell RT-PCR experiments revealed the presence of the AMPA-R subunits GluR1, GluR2, and GluR3 in Purkinje neurons in cerebellar slices at developmental stages corresponding to those studied electrophysiologically. The expression of GluR2 in all cells tested (n = 14) is consistent with the subunit composition predicted from studies of recombinant AMPA-R channels with a low permeability for Ca2+ (Burnashev et al., 1992b). In conclusion, this study establishes that cerebellar Purkinje neurons at all postnatal developmental stages possess AMPA-R channels with a low permeability for Ca2+.
Tempia
F
F
I. Physiologisches Institut, Universität des Saarlandes, Homburg, Germany.
Kano
M
M
Schneggenburger
R
R
Schirra
C
C
Garaschuk
O
O
Plant
T
T
Konnerth
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002531:Cerebellum / Q000502:physiology*; D007608:Kainic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010539:Permeability; D011188:Potassium / Q000494:pharmacology; D011689:Purkinje Cells / Q000502:physiology; D051381:Rats; D018091:Receptors, AMPA / Q000502:physiology*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D015220:Calcium Channels; D018091:Receptors, AMPA; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D011188:Potassium; D007608:Kainic Acid; D002118:Calcium