Figure 4.

Structure–activity relation of suramin analogues for reversing the isoproterenol-induced inhibition of [¹²⁵I]CYP binding to rat cardiac membranes. Rat cardiac membranes (12 μg) were incubated with 75 pM of [¹²⁵I]CYP in the absence and presence of suramin (•), NF503 (▪), NF449 (▴), NF445 (▵), and 100 μM GTP[γS] (▿). At each concentration of the compounds, specific[¹²⁵I]CYP binding was determined in the absence and presence of 30 nM isoproterenol, and the ratio of these two values is given as % (to account for the ∼1.2-fold increase in [¹²⁵I]CYP binding induced by the suramin analogues and GTP[γS]). Data are means of four independent experiments; error bars indicate SD.