Fig. 2. Scatchard analysis and pharmacological profile of [³H]-IP₃ binding to Drosophila melanogaster microsomal membrane fractions. Experiments were performed with 100 µg of microsomal protein and the presence of 1-120 nM (A) or 3 nM [³H]-IP₃ (B) as described in Materials and Methods. Panel A illustrates a hyperbolic saturation curve as a function of increasing IP₃ concentrations. The inset shows a linear Scatchard plot. This is a representative experiment from a total of 5. Panel B depicts the inhibitory effect of 1 mg/ml heparin, 75 µM 2-APB and 5 µM xestospongin C on [³H]-IP₃ binding. The results in Panel B are expressed as mean±s.e.m. of at least four independent experimental observations.