Figure 1.
Subunit-dependent differences in stargazin-dependent autoinactivation of AMPA receptors.
(A–D) Steady-state concentration-response curves of l-glutamate-triggered current responses of homomeric GluA1i (A), GluA2i (B), GluA3i (C) GluA4i (D) channels coexpressed with stargazin. (E) Concentration-response curves of l-glutamate-triggered peak responses of homomeric GluA1-4i receptors. Currents were normalized to the maximal response obtained for each channel. The points represent the mean ± S.E.M of recordings from 5–6 cells from a typical experiment.
Figure 2.
Absence of autoinactivation in homomeric and heteromeric GluA2 channels.
(A) Representative current traces from patch clamp recordings of homomeric GluA2i and GluA4i channel responses to glutamate (10 mM) and kainate (0.7 mM) in the presence (red traces) and in the absence (blue traces) of stargazin. (B) Concentration-response curves of peak (open circles) and steady state (filled circles) l-glutamate responses of homomeric GluA2o channels coexpressed with stargazin. (C) Concentration-response curves of peak (open circles) and steady state (filled circles) l-glutamate responses of heteromeric GluA1i/A2i channels coexpressed with stargazin; (D) Rectification properties of heteromeric GluA1i/GluA2i (left), homomeric GluA1i (middle), and homomeric GluA2i (right) channels, all in the presence of stargazin. Representative traces of glutamate-evoked currents at holding potentials of +40 mV, 0 mV, and −60 mV are shown. The inset shows an enlarged view of GluA1i steady-state currents.
Figure 3.
Autoinactivation of GluA4i - stargazin complex is not affected by covalent linkage between the proteins.
(A) Schematic structure of GluA4i, stargazin and GluA4i-stargazin fusion protein. Amino acid sequence of the linkage between the carboxyterminus of GluA4 and the aminoterminus of stargazin is shown below the cartoon. (B) Western blot of GluA4i, stargazin and GluA4i-stargazin fusion protein detected by using anti-Flag (upper panel) and anti-stargazin (lower panel) antibodies. Molecular size markers (in kilodaltons) are indicated at the right. (C–D) Current-voltage relations of responses to l-glutamate (1 mM) in oocytes expressing the covalent GluA4i-stargazin fusion protein (black), and GluA4i expressed alone (blue) or in the presence of stargazin (red). (E) Concentration-response curves of l-glutamate -triggered currents in oocytes expressing the covalent GluA4i-stargazin fusion protein (black), and GluA4i expressed alone (blue) or in the presence of stargazin (red). The data represent the mean ± S.E.M of recordings from 3–9 oocytes.
Figure 4.
Active and passive AMPA receptor -TARP complexes.
AMPA receptor (green Y) and TARP (blue trapezoid) are shown in schematic fashion. The arrows indicate the potential interconversions between the different states.