Fractional contribution of calcium to the cation current through glutamate receptor channels.
The Ca2+ fraction of the ion current flowing through glutamatergic NMDA and AMPA/kainate receptor channels was determined in forebrain neurons of the medial septum. The neurons were overloaded with the Ca2+ indicator dye fura-2 (1 mM) via the recording patch pipettes. This approach allowed the direct determination of the Ca2+ influx from changes in the Ca(2+)-sensitive fura-2 fluorescence. We found that, at negative membrane potentials and at an extracellular free Ca2+ concentration of 1.6 mM, the Ca2+ fraction of the current through the NMDA receptor channels is only 6.8%, about 2-fold lower than previously estimated from reversal potential measurements. Interestingly, a quite high fractional Ca2+ current of 1.4% was determined for the linearly conducting AMPA/kainate receptor channels found in these neurons.
Schneggenburger
R
R
I. Physiologisches Institut, Universität des Saarlandes, Homburg Federal Republic of Germany.
Zhou
Z
Z
Konnerth
A
A
Neher
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002412:Cations / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology; D007473:Ion Channels / Q000502:physiology*; D009474:Neurons / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA; D017470:Receptors, Glutamate / Q000378:metabolism / Q000502:physiology*; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D012688:Septum Pellucidum / Q000166:cytology / Q000378:metabolism
D002118:Calcium; D002412:Cations; D007473:Ion Channels; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate