Pharmacological Characterization of Inositol 1,4,5-tris Phosphate Receptors in Human Platelet Membranes

Table 2

Displacement of [³H]Ins(1,4,5)P₃ binding by inositol phosphates and heparin in human platelet membranes. Platelet membranes were prepared as described in Section 2. The assay medium (100 𝜇L) contained 20 nM [³H]Ins(1,4,5)P₃ with various concentrations of competitive substances and approximately 100 𝜇g of protein. Incubations were carried out at 4°C for 10 minutes. IC₅₀ values were calculated by using log probit analysis. The values are the mean ± S.E.M. of three different experiments.

Compound	IC50
—	(𝜇M or ^∗𝜇g/mL)
D-Ins(1,4,5)P3	0.3±0.5
D-Ins(2,4,5)P3	1.90±0.68
GPIP3	4.97±1.83
L-Ins(1,4,5)P3	354.0±37.0
Heparin	36.79±6.0l^∗