Figure 7.

Desensitization properties after transient AMPAR activation using paired-pulse small-spot UV photolysis. A, pEPSCs in response to pairs of 20 μs small-spot illumination pulses using a 10 ms interval. Light intensity of the first pulse (P₁) was varied, whereas the intensity of the second pulse (P₂) was maintained at the highest (saturating) intensity of the first pulse. B, Amplitudes of small-spot pEPSC responses at different distances for P₁ across a dendritic digit in same region as A. Color coding indicates different light intensities as for P₁ in A. Dotted lines show Gaussian fits with FWHMs of 0.55, 0.82, 1.44, and 2.00 μm (for green to black P₁ intensity). Cyan region shows region over which traces in A were collected and averaged. C, Relationships between fractional activation of the first pulse (blue circles) or P₂/P₁ pEPSC amplitude ratio (black triangles) and light intensity. Mean P₂/P₁ amplitude ratios were 0.88 ± 0.04 (n = 6), 0.49 ± 0.05 (n = 6), and 0.30 ± 0.02 (n = 7) for low, medium, high light levels, respectively. D, Relationship between P₂/P₁ pEPSC amplitude ratio and channel open probability (P_open) for 13 cells. Dashed line shows linear regression fit with right-hand intercept of 0.38 for a P_open = 1. E, High-intensity paired-pulse pEPSC responses for various interpulse intervals (2 ms, gray; 5 ms, blue; 10 ms, red; 50 ms, green; 100 ms, black). F, Relationship between 1 − (P₂/P₁), which indicates the fraction of desensitization, and interpulse interval for 10 cells.