Figure 5.
Dependence of cooperativity in IP3 production on the number of PF inputs. A, PF-induced IP3 production was measured by varying the number of stimuli (1, 3, 5, 10, 20, and 40 stimuli) at 50 Hz in the absence and the presence of either 4-CPG (1 mm) or NBQX (10 μm). Traces are the averaged time courses of ΔF/F0 within the cytoplasm on PF stimulation. The onset of PF stimulation is indicated by the arrow. B, Peak values of ΔF/F0 (measured during 2.5 sec from the onset of PF stimulation) are plotted against the number of stimuli (mean ± SEM; n = 9-11). Data points were fitted using Hill's equation. C, Cooperativity in IP3 production during varying numbers of PF stimulation. The linear sums of the averaged traces in the presence of 4-CPG or NBQX are compared with averaged traces under the control condition. PF stimulation (1, 3, 5, 10, 20, and 40 stimuli at 50 Hz, from top left to bottom right) is indicated by the gray bar. Results from 11 experiments (control), 9 experiments (4-CPG), and 9 experiments (NBQX) are summarized.