Figure 3. Homeostatic Increase in Ca²⁺ Influx at cac^TS2 Mutant Synapses.

(A) Representative traces of spatially-averaged Ca²⁺ transients of the indicated genotypes (average of 8–12 scans each).

(B) ΔF/F Ca²⁺ transient peak amplitudes (average and cumulative frequency plot) of control (n=31 boutons; gray), cac^TS2 (n=32; light blue), and cac^TS2; GluRIIA^SP16 (n=32; dark blue). All data were collected at room temperature. The peak amplitudes of cac^TS2 mutants, and cac^TS2; GluRIIA^SP16 double mutants were smaller than in control (both p<0.004), and there was a significant difference in peak amplitude between cac^TS2 mutants, and cac^TS2; GluRIIA^SP16 (p=0.007). Note that cac^TS2; GluRIIA^SP16 double mutants display normal synaptic homeostasis at room temperature (see D) (Frank et al., 2006).

(C) Average baseline fluorescence (‘F_base’) and decay time constant (‘τ’) of the groups introduced in (B).

(D) Average mEPSP amplitude (‘mEPSP’), Ca²⁺-transient peak amplitude of (‘ΔF/F’), and quantal content of cac^TS2; GluRIIA^SP16 double mutants normalized to cac^TS2. Electrophysiology data is based on a separate set of experiments (control: n=13; cac^TS2: mEPSP=1.0±0.01 mV; EPSP=42.9±1.8 mV, n=15; cac^TS2; GluRIIA^SP16: mEPSP=0.44±0.03 mV; EPSP=43.6±4.0 mV, n=8).