Figure 5

Effects of rapacuronium on low-affinity ACh binding and [³H]NMS binding. Binding of 1 nM [³H]NMS to membranes from CHO cells expressing individual subtypes of muscarinic receptors was measured in the presence of rapacuronium at the concentrations indicated on the x-axis. Data are expressed as percent of specific binding in the absence of rapacuronium. Symbols represent binding of [³H]NMS (circles), and [³H]NMS in the presence of 10 μM GTPγS and 100 μM (squares) or 200 μM (triangles) ACh. Binding of [³H]NMS was decreased by 100 μM ACh to 71, 64, 59, 60 and 56% and by 200 μM ACh to 55, 47, 42, 43 and 39% at M₁ to M₅ receptors, respectively. Bigger divergence of curves denotes stronger negative cooperativity between ACh and rapacuronium binding. Data are means ± SE from 3 independent experiments performed in quadruplicates. Curves are fits of Eq. 3 (circles) and Eq. 4 (squares and triangles) to data prior to normalization. Binding parameters are summarized in Table 3.