FIGURE 2.

Distinct sources of Ca²⁺ influx are responsible for depolarization-induced Thr-840 and Ser-845 dephosphorylation. A, a 10-min bath application of Ca²⁺-free ACSF containing 10 mm EGTA (indicated by the bar) blocks excitatory synaptic transmission (n = 4). Traces show example fEPSPs recorded during base line and after application of Ca²⁺-free ACSF. B, slices were either untreated (UT) or exposed to high-K⁺ (K) ACSF in the absence and presence of 10 mm EGTA (Ca²⁺-free, 10 min pretreatment) (n = 5; *, p < 0.05 compared with % dephosphorylation in absence of EGTA). Ca²⁺-free ACSF had no effect on basal levels of GluA1 Thr-840 (pT840) and Ser-845 (pS845) phosphorylation or total GluA1 levels. C, inhibiting Ca²⁺ release from intracellular stores with thapsigargin (TG) had no effect on high-K⁺ induced GluA1 dephosphorylation at Thr-840 and Ser-845. Slices were pretreated (for 1 h) with ACSF containing either 0.1% DMSO (vehicle control, n = 6) or 2.0–5.0 μm thapsigargin (n = 4 and 2, respectively). Thapsigargin had no effect on total GluA1 levels or basal levels of GluA1 phosphorylation at Thr-840 and Ser-845. D, high-K⁺ was applied in the absence (control, n = 8) or presence of either 50 μm D-APV (n = 5) or 3 mm CoCl₂ (n = 3). Although blocking VGCC with Co²⁺ inhibited depolarization-induced dephosphorylation at both Thr-840 and Ser-845, blocking NMDARs with APV only prevented dephosphorylation of GluA1 at Ser-845 (**, p < 0.001 compared with % dephosphorylation in controls). APV and CoCl₂ had no effect on basal levels of GluA1 phosphorylation at either site, and total GluA1 levels were unchanged in all conditions. E, bath application of ACSF containing 3.0 mm CoCl₂ abolishes synaptic transmission (n = 4). Traces show fEPSPs recorded during base line and 10 min after application of ACSF containing CoCl₂.