Figure 8. Comparison of the InsP₃ dose relationship to the rate of Ca²⁺ rise.

The responses are plotted either against laser power expressed in absolute units (A) or against the relative [InsP₃] calculated from our model (B). The mean secretory pole responses (n = 12 cells, •, error bars are s.e.m.) and the mean of the active basal pole responses (n = 4, ▪, error bars are s.e.m.) are shown. The points indicated by the asterisks were significantly different at P < 0.05 (Student's one-tailed t test), all other points were not. The units of the InsP₃ dose are relative [InsP₃], estimated as described in Methods and illustrated in Fig. 1. From the injected concentrations of caged InsP₃ we would estimate the maximum [InsP₃] to be 10-50 μm.