Ligand-binding capacity in cultured PASMCs. Ligand binding of ¹²⁵I-VIP as a function of concentration to membranes of PASMCs cultured from healthy controls (n = 3) (a) and PPH patients (n = 3) (b). Cells (10⁶) were incubated for 60 min at 4°C in the presence or absence of unlabeled VIP (100 nM) with the various radioligand concentrations (0.01–20 nM). TB, total binding; NSB, nonspecific binding; SB, specific binding. (a) The data of controls, where the specific binding is below 0.3 pmol/6 × 10⁶ cells; (b) PPH cells with an average specific binding well above 0.6 pmol/6 × 10⁶cells.