Effect of poly-D-lysine (PDK) on the inhibition of [3H]GBC binding to SUR1 by OCoA. Experiments (n=5) were performed in the absence of MgATP with membranes sonicated with the OCoA concentration indicated or with buffer before the addition of PDK (0 or 100 μg ml−1); [3H]GBC was ∼1 nM, BS ∼2 pmol mg−1 and BNS<10% BTOT. Individual experiments were analysed according to Equation (1); after averaging, IC50 values of 8.9 (8.1,9.8)/7.8 (6.5, 9.3) nM and Hill coefficients of 2.1±0.2/2.1±0.2 were obtained in the absence/presence of PDK. PDK increased [3H]GBC binding to 131±2% of control. Inset: Increase in [3H]GBC binding by PDK. Evaluation of the concentration dependence (n=4–9 per point) gave the following parameters: EC50=8.3 (7.9,8.7) μg ml−1, maximum increase=28±1%; Hill coefficient=2.5±0.2.