Figure 2.

Emergence of the effect of gallamine on the binding of N-[³H]methylscopolamine to solubilized M₂ receptor from porcine atria. Gallamine and [³H]NMS (10 nM) were mixed simultaneously with aliquots of the extract, and total binding was measured after incubation of the reaction mixture at either 30 °C (■) or 37 °C (□) for different times as follows: 3 h (A), 6 h (B), 9 h (C), 15 h (D), 21 h (E), and 30 h (F); total binding also was measured after incubation of the reaction mixture for 1 wk at 4 °C (B, inset). The solid lines depict the best fit of Equation 3 (n = 3) to all data acquired at the same temperature, and the parametric values are listed in Table 3. The fitted curves in panels B–E are reproduced as the broken lines in panels A (30 °C) and F (37 °C). The asymptotic values of Equation 3 at each time of incubation are compared in the insets to panels C (30 °C) and D (37 °C) (Y_[G]→0, hatched bars; Y_[G]→∞, solid bars). Details regarding the normalization of the data are described under ‘Experimental Procedures.’